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Diego AROSIO

Professore Associato
Dipartimento di Scienze Chimiche e Geologiche - Sede Dipartimento di Scienze Chimiche e Geologiche

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Pubblicazioni

2023 - Geophysical techniques for monitoring the climate change effects on groundwater availability and quality [Abstract in Atti di Convegno]
Sabattini, Marco; Ronchetti, Francesco; Arosio, Diego; Brozzo, Gianpiero; Panzani, Andrea
abstract

2022 - Analytical Models and Laboratory Measurements to Explore the Potential of GPR for Quality Control of Marble Block Repair through Resin Injections [Articolo su rivista]
Izadi-Yazdanabadi, M.; Hojat, A.; Zanzi, L.; Karimi-Nasab, S.; Arosio, D.
abstract

This work aims to analyze theoretically and with laboratory tests the sensitivity of high-frequency GPR (Ground-Penetrating Radar) to resin injections used in the building and ornamental stone industries to repair marble blocks before final slab cutting. We simulate uniform fractures in the laboratory using small regular marble blocks and we compare the results of GPR tests with the analytical model of the thin bed reflections. We performed two series of GPR surveys with a 3 GHz antenna, progressively increasing the fracture thickness from 0.25 mm to 16 mm, to analyze the results on two simulated conditions: open fracture and repaired fracture. The repaired condition was simulated by substituting the resin layer with polyvinyl chloride (PVC) sheets because the permittivity of PVC is quite similar to the permittivity of epoxy resin. According to the analytical models, when a thin air-filled fracture is filled with resin, the received signal amplitude is expected to decrease by 33% (26% if resin is simulated with PVC). The results showed a very good match between the predictions and the real data observations when the fracture is thicker than 4 mm. Although the analytical and laboratory results show some deviations when the fracture is thinner than 4 mm, the qualitative trend of the amplitude variations is still consistent with the predictions and the 3 GHz antenna can resolve the change in the filling material down to the minimum tested thickness (0.25 mm). As a result, our findings validate the GPR method as a proper tool for nondestructive quality control of resin injections in marble fractures.

2022 - Designing the Expanded Microseismic Monitoring Network for an Unstable Rock Face in Northern Italy [Articolo su rivista]
Zhang, Z.; Arosio, D.; Hojat, A.; Zanzi, L.
abstract

The microseismic monitoring technique is capable of providing important information for revealing the fracture propagation within the rock mass on unstable rock slopes, and thus giving early warning alarms for rockfall hazards. In order to reliably locate microseismic events induced by fracturing, network geometry should be carefully designed. We applied a simplified method to densify a small microseismic network that is currently in operation with five three-component geophones for monitoring an unstable rock face in Northern Italy. In order to calculate the location accuracy, synthetic data affected by random noise were used. The noise level was properly calibrated based on real seismic shots. Considering the constraints on the number of the available channels, 10 additional geophones could provide an acceptable location error within 4–6 m. We also compared the channel performance of the five three-component geophones to explore the preferable orientation of future additional geophones.

2022 - Laboratory tests with interferometric optical fibre sensors to monitor shallow landslides triggered by rainfalls [Articolo su rivista]
Longoni, L.; Ivanov, V.; Ferrario, M.; Brunero, M.; Papini, M.; Arosio, D.
abstract

Optical fibre–based sensors have now established their place in the field of geohazard monitoring due to their sensitivity to strain and temperature changes. Progressive development in the technology leads to the availability of novel, accurate and durable sensors at a relatively limited cost. This creates room for original monitoring applications that have been, so far, impeded by the shortcomings of conventional monitoring tools. In this work, we explore the applicability of an interferometric optical fibre sensor as a vibration sensing tool at laboratory scale. We tested the ability of the sensor to identify precursors of instability in a downscaled model of a rainfall-induced landslide composed of granular material. We carried out four experimental tests which involved different sensor deployments and soil mixtures. The recorded signals were processed by means of a time–frequency analysis and we identified two frequency-domain parameters—the spectral centroid and band power—that could provide information on the development of instability. Their ratio yielded a unique parameter through which a precursory stage could be outlined by defining a threshold value based on the data collected at the beginning of the experiment. In our lab tests, precursors of instability were detected 2–3 min before a crack was observed at the surface. This may upscale to a lead time of about 20–30 min or more in the field, classifying our monitoring approach in between an alarm and a warning system. The work presented here can be considered a first promising step towards an innovative monitoring system and shows the potential of optical fibre sensing as a shallow landslide monitoring technique, encouraging further testing, especially in real-case studies.

2022 - Multidisciplinary non-invasive investigations to develop a hydrogeological conceptual model supporting slope kinematics at Fontana Cornia landslide, Northern Apennines, Italy [Articolo su rivista]
Aguzzoli, Alessandro; Arosio, Diego; Mulas, Marco; Ciccarese, Giuseppe; Bayer, Benedikt; Winkler, Gerfried; Ronchetti, Francesco
abstract

A multidisciplinary approach focusing on the integration of diverse and non-invasive investigations is presented to define the hydrogeological conceptual model of the complex Fontana Cornia landslide in the Northern Apennines, Italy. The results of seismic refraction tomography and electrical resistivity tomography investigations indicate that the landslide has a curvilinear sliding surface dividing the shallow calcarenite debris layer from the deeper pelitic bedrock. The surface presents undulations in which water can be stored and supports the application of the fill and spill hypothesis that is seldom used in landslide studies. The joint interpretation of the geophysical outcomes and of the hydrogeological and hydro-chemical analyses of a spring located on the slope allows the definition of the landslide hydrogeological conceptual model. Four specific hydrologic stages with different groundwater flows though the landslide body were identified. The developed hydrogeological model may explain the displacements of the landslide that were detected with In-SAR monitoring. The isotopes analyses, the displacement monitoring, and the hydrogeological measurements confirm that periods with significant precipitations and snowmelt can cause an increase in landslide saturation that in turn triggers larger displacements. Conversely, the landslide slowly moves at a steady rate during periods with limited recharge water.

2021 - Applicability of an interferometric optical fibre sensor for shallow landslide monitoring – Experimental tests [Articolo su rivista]
Ivanov, V.; Longoni, L.; Ferrario, M.; Brunero, M.; Arosio, D.; Papini, M.
abstract

Optical fibre-based sensors have found a variety of applications throughout engineering and science in the measurement of strain and temperature. Current commercially available sensing technologies are able to provide strain measurements in the order of microstrain across tens of kilometres of range. The strong demand for reliable sensing tools in engineering geology allowed for the advancement of the optical fibre technology which has settled in this field during the past decade. Among the variety of sensing approaches, interferometric fibre optic sensors have rarely been tested for detection of ground movement. In this work we present the results of six laboratory scale experiments in which simulated rainfall induced shallow landslide model made up of non-cohesive soil is equipped with a newly developed coherent fibre optic sensor. Results indicate that a phase of early precursors of instability could be identified by the sensors in all six experiments, two to eight minutes before slope failure. The sensing system proved to be reliable in detecting the evolution of slope stability at shallow depths of up to a few meters depending on the sensors' burial depth, hence stating the emergence of a simple and cost-effective approach for detailed strain monitoring. The proposed sensing technique could therefore provide a viable and cheaper alternative to commercially available optical fibre interrogators and furnish quantitative monitoring data for shallow landslide monitoring in soil-like materials. In order to be efficient for the detection of such failures with a significant precursory window, sensors should ideally be placed in the vicinity of a sliding surface or landslide boundary, which is an achievable task given the high sensing range and multiplexing capabilities of optical fibre sensors.

2021 - Inversion of Synthetic and Measured 3D Geoelectrical Data to Study the Geomembrane below a Landfill [Relazione in Atti di Convegno]
Aguzzoli, A.; Fumagalli, A.; Scotti, A.; Zanzi, L.; Arosio, D.
abstract

2021 - Laboratory studies using electrical resistivity tomography and fiber optic techniques to detect seepage zones in river embankments [Articolo su rivista]
Hojat, A.; Ferrario, M.; Arosio, D.; Brunero, M.; Ivanov, V. I.; Longoni, L.; Madaschi, A.; Papini, M.; Tresoldi, G.; Zanzi, L.
abstract

We present the results of laboratory experiments on a down-scaled river levee constructed with clayey material collected from a river embankment where a permanent resistivity instrument has operated since 2015. To create potential seepages through the levee, two zones (5 × 4 cm and 10 × 2 cm) were filled with sand during the levee construction. Electrical resistivity tomography (ERT) technique and Fiber Bragg Grating (FBG) technology were used to study time-lapse variations due to seepage. The ERT profile was spread on the levee crest and the Wenner array with unit electrode spacing a = 3 cm was used. Six organic modified ceramics (ORMOCER) coated 250 µm-diameter fibers were deployed in different parts of the levee. Time-lapse measurements were performed for both techniques from the beginning of each experiment when water was added to the river side until the water was continuously exiting from the seepage zones. The results showed that ERT images could detect seepages from the early stages. Although with a short delay compared to ERT, fiber optic sensors also showed their ability to detect water infiltrations by measuring temperature changes. Both technologies being successful, a discussion about respective peculiarities and pros and cons is proposed to suggest some criteria in choosing the proper technique according to the specific needs.

2021 - Nuove evidenze sulla circolazione idrica sotterranea delle fonti carsiche di Poiano (Appennino reggiano) [Monografia/Trattato scientifico]
Ronchetti, Francesco; Deiana, Manuela; Lugli, Stefano; Critelli, Vincenzo; Arosio, Diego; Mussi, Mario; Longoni, Laura; Ivov Ivanov, Vladislav; Taruselli, Marco; Brambilla, Davide; Curotti, Alessandra; Bergianti, Stefano; Ercolani, Massimo; Sansavini, Baldo
abstract

2021 - Optimal Design for Expanding a Microseismic Monitoring Network on an Unstable Rock Face in Northern Italy [Relazione in Atti di Convegno]
Zhang, Z.; Arosio, D.; Hojat, A.; Zanzi, L.
abstract

Microseismic monitoring is an efficient method in understanding the stability of rock slopes and it has been increasingly applied in this field in recent years. An optimal network distribution could effectively improve the efficiency of a microseismic monitoring system, especially to increase the localization accuracy of seismic events. In this work, the widely accepted guidelines were used to densify a microseismic network composed of five three-component geophones, which has been working on an unstable rock face in Northern Italy since 2013. The existing 5-geophone network was progressively expanded to a 15-geophone network. The location accuracy was calculated by using synthetic data for each network. We compared the location accuracy for different networks to estimate their performance. The results showed that the additional geophones could decrease the location errors from 12–24 m for the 5-geophone network down to 4–6 m for the 15-geophone network. We also compared the channel performance of the five three-component geophones to select the channels that should be retained in the future expanded network.

2021 - Reclassification of microseismic events through hypocenter location: Case study on an unstable rock face in northern Italy [Articolo su rivista]
Zhang, Z.; Arosio, D.; Hojat, A.; Zanzi, L.
abstract

Passive seismic methods are increasingly used in monitoring unstable rock slopes that are likely to cause rockfalls. Event classification is a basic step in microseismic monitoring. However, the classification of events generated by the propagation of fractures and rockfalls is still uncertain due to their similar features in the time and frequency domains. Hypocenter localization might be a powerful tool to distinguish events generated by fracture propagation from those caused by rockfalls. In this study, a classification procedure based on hypocenter location was validated using a selected subset of high-quality data recorded by a five-geophone network installed on a steep rock slope in Northern Italy. Considering the complexity and heterogeneity of the rock mass, a 3D velocity model that was derived from a tomographic experiment was used. We performed the localization using the equal differential time method. The location results fairly fit our expectations on suspected rockfall events because most signals were located near the rock face. However, only 4 out of 20 suspected fracture events were unquestionably confirmed as fractures being located inside the rock mass and far enough from the rock face. Further improvements in location accuracy are still necessary to distinguish suspected fracture events located close to the rock face from rockfalls. This study demonstrates that hypocenter location is a promising method to improve the final classification of microseismic events.

2021 - Seismic Noise Azimuthal Spectral Ratios to Monitor Landslide Kinematics [Relazione in Atti di Convegno]
Aguzzoli, A.; Zanzi, L.; Arosio, D.
abstract

2021 - Seismic noise monitoring of a small rock block collapse test [Articolo su rivista]
Taruselli, M.; Arosio, D.; Longoni, L.; Papini, M.; Zanzi, L.
abstract

We tested the capability of seismic noise to monitor the stability conditions of a small rock block that we forced to fail in four following stages. Ambient vibrations were recorded with a broad-band 3C seismometer placed on top of the block and were processed to analyse their spectral and polarization characteristics with diverse algorithms. To analyse the spectral content of the records, we applied the multitaper method while seismic noise polarization features were investigated by means of the singular value decomposition of the Hermitian spectral density matrix. Numerical modelling was found to add limited value because of the uncertainty in estimating correctly spatial and mechanical features of the rock bridges between the block and the rock mass. Nevertheless, a modelling exercise we performed is in agreement with previous post-failure observations according to which unstable rocks may be coupled to the stable rock mass by rock bridges covering only a few per cent of the total surface of the fractures. Our analyses confirm that, when approaching final collapse, there is a trend of the block eigenmodes towards lower frequencies and show that polarized bands become narrower.

2020 - Groundwater level monitoring tests with seismic interferometry [Relazione in Atti di Convegno]
Taruselli, M.; Aguzzoli, A.; Zanzi, L.; Arosio, D.
abstract

The objective of this work is to evaluate whether the seismic passive interferometry technique can be used to monitor undeground water variations in both unconfined and confined aquifers that present different hydrogeological characteristics. We collected ambient vibrations in two different water catchment fields where the water level has been artificially modified by activating a pre-existing pumping system. We first estimated the seismic velocity variations by means of Stretching technique and then compared the obtained curve with the water table level monitored by the pumping system. For both the analysed case studies, the dV/V curves showed a clear correlation with the water table variations. Moreover, this experiment reveals that different time windows of the correlogram may infer a different composition of the seismic wavefield. Provided that the absolute groundwater depth can be retrieved, the ambient noise interferometry could be employed to develop a continuous water monitoring system with dense networks for better management of the water resource.

2020 - Investigation on the role ofwater for the stability of shallow landslides-insights from experimental tests [Articolo su rivista]
Ivanov, V.; Arosio, D.; Tresoldi, G.; Hojat, A.; Zanzi, L.; Papini, M.; Longoni, L.
abstract

Shallow soil slips are a significant hydrogeological hazard which could affect extended areas of the high-gradient mountainous landscape. Their triggering is highly dependent on the rainfall water infiltration and its further redistribution, as well as the characteristic properties of the soil itself. The complex interaction between those factors generates a considerable degree of uncertainty in the understanding of the governing processes. In this work, we take a small step further towards the untangling of those intricate relationships through observation. The results of a set of 20 downscaled shallow land mass failures are analysed through a principal component analysis and a further detailed look at the resulting parametric trends. Moreover, electrical resistivity tomography measurements are added up to the interpretation of experimental data, by providing a glimpse on the rainfall water infiltration process at the subsurface level. The outcome of this work implies that the coupled interaction between rainfall intensity, hydraulic conductivity and soil moisture gradient is governing the stability of soil and while rainfall intensity and duration are essential instability predictors, they must be integrated with antecedent moisture and site-specific characteristics. A tentative comparison of the dataset with existing rainfall thresholds for shallow landslide occurrence suggests the potential application of experimental tests for thresholds' definition or validation under the appropriate dimensional analysis. A dimensional analysis indicated the interconnection of parameters intrinsic to the problem, and the significance of scale effects in performing a downscaled simulation of land mass failure.

2020 - Monitoring ca lita landslide by means of the ambient seismic noise [Relazione in Atti di Convegno]
Taruselli, M.; Aguzzoli, A.; Zanzi, L.; Arosio, D.
abstract

This study presents the analysis of the ambient seismic noise recorded on the Ca Lita landslide. In this perspective, we coupled the cross-correlation and polarization techniques with the objective of investigating the variations of the unstable slope's characteristics at two different époques. The results of this study revealed that both methods provide useful information to characterize the dynamic conditions of the active landslide. In particular, the combination of the cross-correlation and polarization techniques allow studying the wavefield evolution over time which seems to be a reliable precursor of the landslide's occurrence. Therefore, the obtained results confirm the potential of ambient seismic noise analysis as a reliable tool to improve our capabilities of slopes failure forecasting.

2020 - Non-destructive root mapping: Exploring the potential of gpr [Relazione in Atti di Convegno]
Arosio, D.; Hojat, A.; Munda, S.; Zanzi, L.
abstract

We discuss the potential of Ground Penetrating Radar (GPR) for tree root mapping by presenting the results from three recent studies performed in different sites with secular trees. Depending on the survey area, we discuss the use of two different hardware solutions to perform high density 3D surveys: a single antenna (500MHz or 1GHz) in combination with a PSG (Pad System for Georadar) or a 600MHz array system (IDS Stream C). The results show that GPR method can be an effective tool to map the roots. The approximate extent of the soil volume hosting most of the roots can be easily interpreted after applying a standard data processing sequence. However, advanced image interpretation remains an open issue and, in case a detailed root net reconstruction is needed, the cost of the interpretation phase prevails over the costs of acquisitions and data processing and can significantly affect the overall project costs. Algorithms for automatic root drawing would be the solution but the reliability of such root maps is still to be validated.

2020 - Quantifying seasonal 3D effects for a permanent electrical resistivity tomography monitoring system along the embankment of an irrigation canal [Articolo su rivista]
Hojat, A.; Arosio, D.; Ivanov, V. I.; Loke, M. H.; Longoni, L.; Papini, M.; Tresoldi, G.; Zanzi, L.
abstract

In this paper, we discuss the necessity of quantifying and correcting seasonal 3D effects on 2D electrical resistivity tomography (ERT) data measured along the embankments of rivers or artificial canals. A permanent ERT monitoring system has been continuously operating along the levee of an irrigation canal in Mantua province, Italy, since September 2015. To evaluate the importance of 3D effects and their dependence on seasonal variations, we first performed numerical simulations and also laboratory tests on downscaled levees of the study site. The results showed that 2D apparent resistivity pseudosections measured along the levee are significantly affected by 3D effects of the embankment geometry. Moreover, it was observed that 3D effects not only depend on the levee geometry, but they are also affected by seasonal fluctuations in the water level in the canal. This proved the importance of calculating 3D effects for the study site during dry and irrigation periods. Therefore, different synthetic models based on the levee geometry and water level in the canal in each period were constructed in RES2DMOD and RES3DMODx64 to quantify 3D effects for the study site. The ratios of apparent resistivity values calculated in RES3DMODx64 to the values calculated in RES2DMOD showed that 3D effects approach a maximum of 30% when the canal is empty during winter, and they arrive at a maximum of 10% when the canal is filled with water in summer. Using the graphs of the modelled 3D effects as a function of electrode spacing, apparent resistivity pseudosections measured by the permanent ERT system are corrected for 3D effects to obtain reliable resistivity sections after inversion. The final resistivity maps can be then converted into water content images using the empirical and site-dependent relationship developed from core samples in the study area. Water content maps can be used to evaluate the stability of the levee and to detect possible seepage zones.

2020 - Refining microseismic event classification through hypocentre location [Relazione in Atti di Convegno]
Zhang, Z.; Arosio, D.; Hojat, A.; Zanzi, L.
abstract

Monitoring of unstable rock slopes is a promising application of passive microseismics. Hypocentre localization might be a powerful tool to distinguish events generated by internal stress from rockfalls. However, its application is still a challenging task due to the heterogeneity of fractured rock slopes and the weakness of acoustic emissions generated by stress releases. In this study, we tried to validate a classification procedure based on hypocentre location by testing the approach on a selected subset of high quality data recorded by a five-sensor network installed on a steep rock slope. To properly manage the complexity and heterogeneity of the rock mass, we used a 3D velocity model that was derived from a tomographic experiment. We performed the localization by using the equal differential time method. The location results fairly fit our expectations: suspected rockfall events were mostly located on the rock surface or near the rock surface and suspected fracture events were mostly located inside the rock mass. However, we also observed examples of microseismic events for which our assumptions were wrong and that thanks to location results were correctly classified. This test demonstrates that hypocentre location is a promising method to improve the final classification of microseismic events.

2020 - Tomographic experiments for defining the 3D velocity model of an unstable rock slope to support microseismic event interpretation [Articolo su rivista]
Zhang, Z.; Arosio, D.; Hojat, A.; Zanzi, L.
abstract

To monitor the stability of a mountain slope in northern Italy, microseismic monitoring technique has been used since 2013. Locating microseismic events is a basic step of this technique. We performed a seismic tomographic survey on the mountain surface above the rock face to obtain a reliable velocity distribution in the rock mass for the localization procedure. Seismic travel-time inversion showed high heterogeneity of the rock mass with strong contrast in velocity distribution. Low velocities were found at shallow depth on the top of the rock cliff and intermediate velocities were observed in the most critical area of the rock face corresponding to a partially detached pillar. Using the 3D velocity model obtained from inversion, localization tests were performed based on the Equal Differential Time (EDT) localization method. The results showed hypocenter misfits to be around 15 m for the five geophones of the microseismic network and the error was significantly decreased compared to the results produced by a constant velocity model. Although the localization errors are relatively large, the accuracy is sufficient to distinguish microseismic events occurring in the most critical zone of the monitored rock mass from microseismic events generated far away. Thus, the 3D velocity model will be used in future studies to improve the classification of the recorded events.

2020 - Two dimensional ERT simulations to check the integrity of geomembranes at the base of landfill bodies [Relazione in Atti di Convegno]
Aguzzoli, A.; Hojat, A.; Zanzi, L.; Arosio, D.
abstract

In this paper, we present the results of electrical resistivity tomography (ERT) modellings to study the capability of the method in distinguishing a damaged geomembrane from an intact one below landfills. Different 2D synthetic models were defined in Res2dmod and the geomembrane was placed at a depth of 20-25 m from the ground level. Different scenarios were modelled moving from simple homogeneous landfill body to more realistic landfill above the insulating geomembrane. For each model, simulations were performed both for an intact geomembrane and for a damaged one. For the latter case, an area below the landfill polluted by the leachate was also modelled. Apparent resistivity pseudosections were calculated for the most common electrical arrays and then inverted with Res2dinv software. In this work, we present the results for the dipole-dipole array. The results showed distinguishable contrasts in resistivity values below the landfill between the intact and damaged situations provided that the survey spread is long enough to observe the resistivity values at depths quite larger than the geomembrane depth, especially when a conductive leachate layer is present just above the geomembrane.

2019 - Assessment of 3D geometry effects on 2D ERT data of a permanent monitoring system along a river embankment [Relazione in Atti di Convegno]
Hojat - Politecnico di Milano, A.; Arosio, D.; Loke, M. H.; Longoni, L.; Papini, M.; Tresoldi, G.; Zanzi, L.
abstract

2019 - Construction of a 3D velocity model for microseismic event location on a monitored rock slope [Relazione in Atti di Convegno]
Zhang, Z.; Arosio, D.; Hojat, A.; Taruselli, M.; Zanzi, L.
abstract

2019 - GPR measurements to detect major discontinuities at Cheshmeh-Shirdoosh limestone quarry, Iran [Articolo su rivista]
Zanzi, Luigi; Hojat, Azadeh; Ranjbar, Hojjatollah; Karimi-Nasab, Saeed; Azadi, Asghar; Arosio, Diego
abstract

In recent years, the Iranian rich quarry industry has been looking for efficient scientific investigations to improve the extraction operations in different dimension stone quarries. Kerman Province is one of the most potential zones with a variety of dimension stone quarries near the city of Kerman. In this research, GPR measurements were carried out to detect major discontinuities at Cheshmeh-Shirdoosh limestone quarry, northeast of Kerman city. This quarry is being extracted by the diamond wire sawing method. As the first GPR study in Iranian quarries, a total length of about 1200 m was surveyed with 50 MHz and 250 MHz GPR antennas collecting data on the surface of the three extraction benches of the quarry. A 800 MHz antenna was also used to map the main defects of a block, which was extracted from a fractured section of the quarry. Six parallel profiles at 10 cm intervals were measured along one side of the block. The results obtained from the 250 MHz dataset were very encouraging and could detect all the major discontinuities. Interpreted profiles were also used to prepare depth slices of the density of joints for two main survey areas. As expected, GPR sections obtained from the 50 MHz antenna had a lower resolution but could clearly detect fault zones. The 800 MHz antenna could map the main defects of the extracted block. However, a higher frequency antenna (e.g., 2GHz or more) is recommended for mapping thin fractures.

2019 - GPR method as an efficient NDT tool to characterize carbonate rocks duirng different production stages (Winner best oral EAGE-GMS meeting) [Relazione in Atti di Convegno]
Hojat, A.; Izadi-Yazdanabadi, M.; Karimi-Nasab, S.; Arosio, D.; Zanzi, L.
abstract

Iran and Italy have a great potential in stone production relying on a variety of dimension stone quarries, especially carbonate rocks. To survive in the modern challenging international market, it is crucial to have products without defects. Ground Penetrating Radar (GPR) method as a rapid and efficient non-destructive technique (NDT) can be used to characterize carbonate rocks during different production stages. In this paper, we present the results of GPR measurements to monitor the quality of marble and limestone rocks at different scales. Considering the availability of GPR antennas in a wide range of frequencies, providing different resolutions, GPR method is very encouraging to detect the desired discontinuities of carbonate rocks at different production stages. Lower frequency antennas can detect major discontinuities to optimize the extraction design. Higher frequency antennas can later detect smaller fractures of the extracted blocks to optimize slab production. Our research is under progress to explore the efficiency of GPR method in mapping the quality of resin injection in fractured rocks. As an auxiliary NDT method to be integrated with GPR measurements, ultrasonic pulse velocity tests are also performed. The results show that changes in the velocity can be a good indication of the stone quality.

2019 - GPR method as an efficient NDT tool to characterize carbonate rocks during different production stages [Relazione in Atti di Convegno]
Hojat, A.; Izadi-Yazdanabadi, M.; Karimi-Nasab, S.; Arosio, D.; Zanzi, L.
abstract

2019 - Geoelectrical characterization and monitoring of slopes on a rainfall-triggered landslide simulator [Articolo su rivista]
Hojat, A.; Arosio, D.; Ivanov, V. I.; Longoni, L.; Papini, M.; Scaioni, M.; Tresoldi, G.; Zanzi, L.
abstract

2019 - Geological and geophysical investigations to analyse a lateral spreading phenomenon: the case study of Torrioni di Rialba, northern Italy [Articolo su rivista]
Arosio, D.; Longoni, L.; Papini, M.; Bievre, G.; Zanzi, L.
abstract

We combined geological, geomechanical, geophysical and remote sensing investigations, including persistent scatterer interferometry and bathymetry, to study a slope where four conglomerate towers laterally spread over a shale layer. Electrical resistivity tomography surveys confirm a shale layer that underlies the rock towers with an attitude parallel to the slope. Field mapping reveals that the stability of the rock towers is threatened by weakly cemented conglomerate layers, large eroded zones and karstic weathering due to water circulation. We deem that the most probable failure mechanism would be the toppling of the southernmost tower, promoted primarily by the weak conglomerate layer in its lower section. The plastic shale layer underneath the rock cliff is very likely to promote lateral spreading that may have triggered the toppling of an additional former rock pillar, whose rock blocks were found in the lake during a bathymetric survey. Close- and long-range remote sensing of displacements provide no results that could be interpreted with confidence. Seismic noise recording sessions with 3C low-frequency velocimeters suggest that the dynamic conditions of the towers do not show appreciable variations across the recording sessions, especially considering the two rock towers featuring the most interesting spectral characteristics. However, both the resonance frequencies and the preferential oscillation directions estimated from the seismic noise datasets are consistent with the analytical relationships and will support the design of an effective monitoring strategy.

2019 - Installation and validation of a customized resistivity system for permanent monitoring of a river embankment [Relazione in Atti di Convegno]
Hojat - Politecnico di Milano, A.; Arosio, D.; Longoni, L.; Papini, M.; Tresoldi, G.; Zanzi, L.
abstract

2019 - Long-term hydrogeophysical monitoring of the internal conditions of river levees [Articolo su rivista]
Tresoldi, G.; Arosio, D.; Hojat, A.; Longoni, L.; Papini, M.; Zanzi, L.
abstract

To evaluate the vulnerability of the earthen levee of an irrigation canal in San Giacomo delle Segnate, Italy, a customized electrical resistivity tomography (ERT) monitoring system was installed in September 2015 and has been continuously operating since then. Thanks to a meteorological station deployed at the study site, we could investigate the relationship between the inverted resistivity values and different parameters, namely air temperature, rainfall and water level in the canal. Air temperature seems to have a minor but not negligible influence on resistivity variations, especially at shallow depth. A model of soil temperature versus depth was used to correct resistivity sections for air temperature variations through the different seasons. Changes of the water level in the canal and rainfall significantly affect measured resistivity values. At the study site, the most important variations of resistivity are related to saturation and dewatering processes in the irrigation periods. Although we explored the effect of drawdown procedures on resistivity data, this process, causing rapid variations of resistivity values, is still not completely understood because the canal is rapidly emptied during rainfall events. Therefore, the effect of variations of the water level in the canal on levee resistivity cannot be distinguished from the effect of rainfalls. To study the effect of water level variations alone, we considered the beginning of the irrigation period when the dry canal is gradually filled and we observed a smooth trend of resistivity changes. The effect of rainfall on the data was studied during different periods of the year and at different depths of the levee so that the resistivity variations could be evaluated under different conditions. To convert the inverted resistivity sections into water content maps, an empirical and site-dependent relationship between resistivity and water content was obtained using core samples. Water content data can then be used for the implementation of stability analysis using custom modeling. This study introduces an efficient technique to monitor earthen levees and to control the evolution of seepage and water saturation in pseudo-real time. Such a technique can be exploited by Public Administrations to reduce hydrogeological risks significantly.

2019 - Raspberry shake sensor field tests for unstable rock monitoring [Relazione in Atti di Convegno]
Taruselli, M.; Arosio, D.; Longoni, L.; Papini, M.; Zanzi, L.
abstract

In this work, we evaluate the performance of the Raspberry Shake 3D (RS-3D) seismometer in estimating the resonance frequencies of unstable rock blocks. In this perspective, we compared this low-cost sensor with the Nanometrics Trillium Compact 20s to assess whether RS-3D is suitable for the development of reliable rock monitoring systems. We carried out surveys on eight rock compartments located both in the Northern Italy and in the Maltese archipelago. Ambient noise recordings have been processed by computing the mean amplitude spectra, the ratio between the Raspberry Shake spectra and the Trillium ones, and the Horizontal-to-Vertical Spectral Ratio. The obtained results show that the RS-3D performs according to the vendor specifications, with slight spectral differences with respect to the Nanometrics reference. Our preliminary tests reveal that the Raspberry Shake may be a reliable sensor for estimating the fundamental frequency of unstable rock blocks provided the HV peak occurs within the RS flat frequency response, and, because of its low-cost, may promote the deployment of denser seismic monitoring networks.

2019 - Seismic noise polarization analysis for unstable rock monitoring [Relazione in Atti di Convegno]
Arosio, D.; Taruselli, M.; Longoni, L.; Papini, M.; Zanzi, L.
abstract

In this work, we discuss three different approaches to investigate the polarization characteristics of ambient vibrations collected on unstable rock slopes for monitoring purposes. We consider the Principal Component Analysis (PCA) of the time-domain covariance matrix, the Horizontal-to-Vertical Spectral Ratio as a function of Azimuth (HVSRA), as well as the Singular Value decomposition (SVD) of the Hermitian spectral density matrix. A simple test taking into account seismic noise datasets collected in two acquisition sessions on a potentially unstable rock pillar suggests that the latter method is able to provide more information with respect to the PCA and HVSRA approaches. Processing of the spectral density matrix allows to estimate frequency-dependent polarization parameters, namely the degree of polarization and four angular quantities describing the particle motion in the 3-dimensional space. Provided that processing is properly tuned, frequency-dependent polarization analysis may be able to track subtle changes of unstable rock vibration modes and so to increase our rock failure forecasting capabilities.

2019 - Seismic noise spectral analysis techniques to monitor unstable rock blocks [Relazione in Atti di Convegno]
Zanzi, L.; Taruselli, M.; Arosio, D.; Longoni, L.; Papini, M.
abstract

2019 - Testing ERT and fiber optic techniques at the laboratory scale to monitor river levees [Relazione in Atti di Convegno]
Hojat, A.; Arosio, D.; Di Luch, I.; Ferrario, M.; Ivov Ivanov, V.; Longoni, L.; Madaschi, A.; Papini, M.; Tresoldi, G.; Zanzi, L.
abstract

In this paper we present the results of laboratory tests using electrical resistivity tomography (ERT) and fiber optic techniques to monitor river levees. A small-scale levee was constructed with the scale of 1:12 based on the earthen levee of an irrigation canal in San Giacomo delle Segnate, Italy, where a customized ERT monitoring system has been operating since September 2015. The most important mechanisms affecting the stability of river levees were simulated during different tests. To explore the possibility of using fiber optic sensors to monitor the integrity of levee structures, Fiber Bragg Grating (FBG) technology was adopted and four Organic Modified Ceramics (ORMOCER) coated 250μm-diameter fibers were deployed at the water exit side of two leakage zones. ERT data from a miniaturized electrode spread show that changes in the water level in river and the rainfall events significantly affect the resistivity distribution in the levee. Using TDR data, the relationship between water content and resistivity values was calibrated to be able to translate the inverted ERT images into water content maps. The results of fiber optic measurements showed the feasibility of fiber optic sensors to detect the deformations of the levee body in response to water infiltration.

2018 - A laboratory experience to assess the 3D effects on 2D ERT monitoring of river levees [Relazione in Atti di Convegno]
Arosio, D.; Hojat, A.; Ivanov, V. I.; Loke, M. H.; Longoni, L.; Papini, M.; Tresoldi, G.; Zanzi, L.
abstract

2018 - Analysis of microseismic signals collected on an unstable rock face in the Italian Prealps [Articolo su rivista]
Arosio, Diego; Longoni, Laura; Papini, Monica; Boccolari, Mauro; Zanzi, Luigi
abstract

In this work we present the analysis of more than 9000 signals collected from February 2013 to January 2016 by a microseismic monitoring network installed on a 300 m high limestone cliff in the Italian Prealps. The investigated area was affected by a major rockfall in 1969 and several other minor events up to nowadays. The network features five three-component geophones and a weather station and can be remotely accessed thanks to a dedicated radio link. We first manually classified all the recorded signals and found out that 95 per cent of them are impulsive broad-band disturbances, while about 2 per cent may be related to rockfalls or fracture propagation. Signal parameters in the time and frequency domains were computed during the classification procedure with the aim of developing an automatic classification routine based on linear discriminant analysis. The algorithm proved to have a hit rate higher than 95 per cent and a tolerable false alarm rate and it is now running on the field PC of the acquisition board to autonomously discard useless events. Analysis of lightning data sets provided by the Italian Lightning Detection Network revealed that the large majority of broad-band signals are caused by electromagnetic activity during thunderstorms. Cross-correlation between microseismic signals and meteorological parameters suggests that rainfalls influence the hydrodynamic conditions of the rock mass and can trigger rockfalls and fracture propagation very quickly since the start of a rainfall event. On the other hand, temperature seems to have no influence on the stability conditions of the monitored cliff. The only sensor deployed on the rock pillar next to the 1969 rockfall scarp typically recorded events with higher amplitude as well as energy. We deem that this is due to seismic amplification phenomena and we performed ambient noise recording sessions to validate this hypothesis. Results confirm that seismic amplification occurs, although we were not able to identify any spectral peak with confidence because the sensors used are not suitable for this task. In addition, we found out that there is a preferential polarization of the wave field along the EW direction and this is in agreement with the geological analysis according to which the pillar is overhanging towards the 1969 rockfall scarp and may preferentially evolve in a wedge failure. Event location was not possible because of the lack of a velocity model of the rock mass. We tried to distinguish between near and far events by analysing the covariance matrix of the three-component recordings. Although the parameters and the outcomes of this analysis should be evaluated very carefully, it seems that about 90 per cent of the considered microseismic signals are related to the stability conditions of the monitored area.

2018 - High-frequency GPR investigations in Saint Vigilius Cathedral, Trento [Relazione in Atti di Convegno]
Arosio, D.; Hojat, A.; Munda, S.; Zanzi, L.
abstract

2018 - Microseismic monitoring of an unstable rock face: Preliminary event location [Relazione in Atti di Convegno]
Zhang, Zhiyong; Arosio, Diego; Hojat, Azadeh; Zanzi, Luigi
abstract

2018 - Rock stability as detected by seismic noise recordings - Three case studies [Relazione in Atti di Convegno]
Taruselli, M.; Arosio, D.; Longoni, L.; Papini, M.; Corsini, A.; Zanzi, L.
abstract

2018 - Tech-Levee-Watch: Experimenting an integrated geophysical system for stability assessment of levees [Articolo su rivista]
Tresoldi, G.; Arosio, D.; Hojat, A.; Longoni, L.; Papini, M.; Zanzi, L.
abstract

The aim of the Tech-Levee-Watch project is to combine geophysical technologies into an integrated system of diagnosis-monitoring-alert related to the vulnerability of earthen levees.A first milestone of the project consists in validating a fast scanning methodology based on a proper combination of portable geophysical instruments tailored to detect possible unstable areas of the levee structures. A second milestone consists in monitoring the most critical sites by installing a low-power fully-automatic geo-resistivity meter prototype programmed for wireless daily transmission of resistivity maps. The third milestone is the calibration of a relation between resistivity values and water content values so that resistivity maps will be transformed into water content maps used to feed a simulator of the levee stability. The final milestone consists of calibrating a set of thresholds in order to define an early-warning procedure to be delivered to administrations and citizens.This procedure can help authorities to organize maintenance of the embankments and to face critical situations that can lead to economic damages and loss of human lives.

2017 - A customized resistivity system for monitoring saturation and seepage in earthen levees: Installation and validation [Articolo su rivista]
Arosio, Diego; Munda, Stefano; Tresoldi, Greta; Papini, Monica; Longoni, Laura; Zanzi, Luigi
abstract

This work is based on the assumption that a resistivity meter can effectively monitor water saturation in earth levees and can be used as a warning system when saturation exceeds the expected seasonal maxima. We performed time-lapse ERT measurements to assess the capability of this method to detect areas where seepage is critical. These measurements were also very useful to design a prototype monitoring system with remarkable savings by customizing the specifications according to field observations. The prototype consists of a remotely controlled low-power resistivity meter with a spread of 48 stainless steel 20 × 20 cm plate electrodes buried at half-meter depth. We deployed the newly-designed permanent monitoring system on a critical levee segment. A weather station and an ultrasonic water level sensor were also installed in order to analyse the correlation of resistivity with temperature, rainfalls and water level seasonal variations. The preliminary analysis of the monitoring data shows that the resistivity maps follow a very reasonable trend related with the saturation/drying cycle of the levee caused by the seasonal variations of the water level in the irrigation channel. Sharp water level changes cause delayed and smooth resistivity variations. Rainfalls and, to a lesser extent, temperature seem to have an influence on the collected data but effects are apparently negligible beyond 1 m depth. The system is currently operating and results are continuously monitored.

2017 - Analysis of thin fractures with GPR: from theory to practice [Abstract in Atti di Convegno]
Arosio, Diego; Zanzi, Luigi; Longoni, Laura; Papini, Monica
abstract

Whenever we perform a GPR survey to investigate a rocky medium, being the ultimate purpose of the survey either to study the stability of a rock slope or to determine the soundness of a quarried rock block, we would like mainly to detect any fracture within the investigated medium and, possibly, to estimate the parameters of the fractures, namely thickness and filling material. In most of the practical cases, rock fracture thicknesses are very small when compared to the wavelength of the electromagnetic radiation generated by the GPR systems. In such cases, fractures are to be considered as thin beds, i.e. two interfaces whose distance is smaller than GPR resolving capability, and the reflected signal is the sum of the electromagnetic reverberation within the bed. According to this, fracture parameters are encoded in the thin bed complex response and in this work we propose a methodology based on deterministic deconvolution to process amplitude and phase information in the frequency domain to estimate fracture parameters. We first present some theoretical aspects related to thin bed response and a sensitivity analysis concerning fracture thickness and filling. Secondly, we deal with GPR datasets collected both during laboratory experiments and in the facilities of quarrying activities. In the lab tests fractures were simulated by placing materials with known electromagnetic parameters and controlled thickness in between two small marble blocks, whereas field GPR surveys were performed on bigger quarried ornamental stone blocks before they were submitted to the cutting process. We show that, with basic pre-processing and the choice of a proper deconvolving signal, results are encouraging although an ambiguity between thickness and filling estimates exists when no a-priori information is available. Results can be improved by performing CMP radar surveys that are able to provide additional information (i.e., variation of thin bed response versus offset) at the expense of acquisition effort and of more complex and tricky pre-processing sequences.

2017 - Classification of Microseismic Activity in an Unstable Rock Cliff [Relazione in Atti di Convegno]
Arosio, Diego; Boccolari, Mauro; Longoni, Laura; Papini, Monica; Zanzi, Luigi
abstract

We installed a microseismic monitoring network on a 300 m high unstable rock face threatening the city of Lecco, in Northern Italy. The network is active since February 2013 and consists of 5 electromagnetic velocimeters, two of which are deployed in boreholes, two temperature sensors in air and in a shallow fracture, and a rain gauge. Regarding the detection of microseismic events, we decided to set the triggering algorithm in order to tolerate false alarms, and, as a consequence, the network has collected several thousands of events so far. Hence, it is necessary to develop an automatic processing scheme able to discard all the recorded events that are not related to the instability of the rock slope. According to the outcomes of previous studies presented in the scientific literature and to careful analysis of the collected data, we first focused on manual classification of recorded signals according to two main classes: a first one grouping events related to the stability conditions of the slope (referred to as MS and local events), and a second one clustering all disturbances (referred to as spikes, mixed event and unclassified noise). Then, we attempted to develop a classification routine in order to cluster possibly all the signals manually classified as MS events, and at the same time having few false positives. The development of classification algorithm involved analysis of parameters in both time and frequency domains, also supported by spectrograms and Radon transform computations, correlation with meteorological datasets, polarization assessment of the 3-component recordings along with principal component analysis. The algorithm we developed has proved to have a satisfactory success rate. We are now focusing on the last step of the microseismic monitoring activity that involves the localization of events related to the instability of the slope.

2017 - Geological Assessment and Physical Model of Complex Landslides: Integration of Different Techniques [Relazione in Atti di Convegno]
Brambilla, Davide; Ivov Ivanov, Vladislav; Longoni, Laura; Arosio, Diego; Papini, Monica
abstract

Complex landslides usually need to be investigated in depth in order to understand the geological setting that led to their formation and influenced their development. The knowledge of the landslide structure and history is the key point to understand potential future development and evolutions. Classical geological tools and campaigns can only give a partial insight and integration of different survey techniques arises as a crucial point to improve knowledge and overcome traditional techniques’ shortcomings. Here, the Torrioni di Rialba (Italy) case study is presented. A vertical 135 m-high rock cliff in Abbadia Lariana, Northern Italy, is suspected to be potentially unstable, although no information about the geological setting is available. Although the landslide has not shown activity evidences in the last decade a possible collapse threatens a narrow corridor of extreme importance. The urge to better understand landslide causes led to start a broad campaign of surveys. Geological investigations were conducted along with geophysical surveys, namely seismic tomography and several electrical soundings, to give an insight in the inner slope structure and were calibrated drilling two boreholes on the slope. An accurate Lidar survey of the area as well as lake bathymetry near the landslide spot allowed for precise geometry assessment of the area to correctly locate information gathered. In this work the weak and strong points of each choice is debated in order to highlight uncertainty in the decisional process and to define good practice and caveats. The entire work, which took four years, due to economical and logistic limitations is critically reviewed and the better choices are underlined.

2017 - Georadar investigations and monitoring of the wall structures and vault system of the Sala delle Asse, in Leonardo da Vinci - The Sala delle Asse of the Sforza Castle [Capitolo/Saggio]
Arosio, Diego; Condoleo, Paola; Cucchi, Marco; Munda, Stefano; Tiraboschi, Claudia; Zanzi, Luigi
abstract

In 2011, the engineer Giuseppe Albano studied the geometry and state of conservation of the structures of the vault system of the Sala delle Asse to assess any damage and instabilities in the room and proposed a series of studies and monitoring for the cracks that had been detected on the extrados of the lower vault and on the vertical structures, with the aim of identifying any movement that might be un­der way. Currently, a diagnostic campaign is in progress, targeted towards understanding the build­ ing technique and structural behaviour of the vault system. Radar studies were conducted to reconstruct the stratigraphy of the system comprising the lunetted cloister vault, the depressed arch cloister vault above and the floor of the room on the upper floor. Other radar studies were conducted to characterize the raised wall structures, which are of notable thickness (even as much as aver 2.5 m) and to identify cavities and a flue that runs along the full height of the north-east wall. A topographical/diagnostic laser scanner survey will make it possible to reveal the critical points of the structures and types of instability and provide understanding of the dynamics of the crack pattern. The stratigraphic reading will make it possible to codify the archaeological sequence of the built structure, the deterioration and state of damage (the contribution The Diagnostic Survey: The Sala delle Asse and its Context in the present volume).The need to speed Up the time spent collecting information that would be useful for safeguarding and protecting the room forced the immediate installation of a system far monitoring cracks based on the information available at the time, which derived from a preliminary survey and the results of thermographic studies (see the contribution The Preliminary Thermo-Hygrometric Research and Environmental Monitoring of the Sala delle Asse in this volume), which revealed a few structural cracks. It will be possible to review or integrate the arrangement of the transducers based on the results of the above-described survey.

2017 - Monitoring bedload sediment transport in a pre-Alpine river: an experimental method [Articolo su rivista]
Longoni, Laura; Arosio, Diego; Brambilla, Davide; Ivanov, Vladislav Ivov; Papini, Monica
abstract

Sediment transport in Alpine and pre-Alpine zones is an essential part of the broad field encompassing hydro-geological instabilities, with particular significance during high intensity rainfall events. This study describes an experimental method for the characterization of the dynamics of this phenomenon at a small spatial and temporal resolution. A set of Radio Frequency IDentificator (RFID) equipped pebbles has been tracked for a period of 6 months and their propagation along the stream has been recorded after each rainfall event. A descriptive database has been devised in order to explore the mobility of the single grains with respect to their geometrical characteristics, their mass as well as the influence of the precipitation intensity on the monitored river reach. Preliminary results indicate the strong correlation of sediment mobility to river discharge and suggest the influence of initial position in terms of morphological characteristics on the sediment mobility.

2017 - RFID-Aided Sediment Transport Monitoring—Laboratory and Preliminary Field Test Results [Relazione in Atti di Convegno]
Ivov Ivanov, Vladislav; Brambilla, Davide; Longoni, Laura; Arosio, Diego; Papini, Monica
abstract

Although often disregarded during natural hazard evaluation, sediment transport phenomena could represent a matter of major significance when dealing with hydro-geological instabilities with possible adverse impacts on river basin management, structural integrity of hydraulic structures, and public safety. Under conditions of high precipitation and consequent propagation of flood waves, the phenomenon is severely intensified, especially in Alpine and pre-Alpine areas, characterized by relatively high slopes and intense sediment supply from the upstream valleys. This study investigates the application of RFID (Radio-Frequency IDentification) transponders (also referred to as tags) as a qualitative and quantitative sediment transport monitoring tool. Preliminary laboratory and field tests have been carried out on both transponders and transponder-equipped pebbles under various conditions of the surrounding environment such as burial and water depth in order to evaluate the performance of the technology. Results of the laboratory experiments indicate that the detection distance depends on the orientation of the tag itself and therefore insertion of two or even 3 tags in a single pebble according to its axes is necessary in order to ensure higher recovery rates. Further, characteristic grain size curves have been used to identify 90 RFID-equipped and painted grains divided in several size classes and used in a first field experiment. The groups have been deployed at predefined locations characterized by similar granulometry and flow conditions. Two recovery campaigns have been since carried out, with the former some 15 h after a relatively intensified rainfall event and the latter two days later. A relatively high recovery rate has been recorded (72% during the first and 78% during the second campaign) to a distance of up to 50 m downstream of the initial deployment point. Despite some limitations, the technology appears to yield promising insights in the more detailed understanding of sediment transport.

2017 - Seismic Noise Measurements on Unstable Rock Blocks: The Case of Bismantova Rock Cliff [Relazione in Atti di Convegno]
Arosio, Diego; Corsini, Alessandro; Giusti, Riccardo; Zanzi, Luigi
abstract

In this work, we tested the use of passive seismic for the characterization of potentially unstable rock blocks in the Pietra di Bismantova site, a wide slab of calcareous sandstone located in the Northern Apennines of Italy. Ambient vibrations recordings with broad-band 3-component seismometers were carried out on potentially unstable areas such as 5 rock blocks and 1 rock column located close to the top of the 100 m-high cliff. The rock blocks are also monitored by means of crackmeters. Seismic noise recordings were processed with a standard sequence and noise spectra and spectral ratios have been evaluated. Preliminary results are promising since in some cases a significant frequency peak can be observed, indicating resonance effects due to the vibration of the rock pillars. In addition, for the most favorable case, noise polarization analysis presents vibration direction values at given frequency in a limited angle range, reasonably corresponding to the direction of maximum displacement. Future investigations could address additional noise measurements and their correlation with the crackmeter datasets in order to understand possible relationship between change in resonance frequency or signal polarization and crackmeter hysteresis path. Moreover, new ambient noise surveys could be planned as a pilot investigation campaign, with the aim of designing extensometer monitoring network tuned on the most critical situations.

2017 - Sperimentazione alla scala di laboratorio per il monitoraggio di frane indotte da precipitazioni con misure geoelettriche time-lapse [Relazione in Atti di Convegno]
Tresoldi, Greta; Arosio, Diego; Brambilla, Davide; Hojat, Azadeh; Ivov Ivanov, Vladislav; Longoni, Laura; Papini, Monica; Scaioni, Marco; Zanzi, Luigi
abstract

Secondo l’Inventario dei Fenomeni Franosi d’Italia (IFFI), al 2016 le frane censite in Italia sono 614.799, interessano un’area pari al 7.5% del territorio nazionale e il 70.5% dei Comuni italiani. Le frane indotte da precipitazioni, inoltre, per la loro evoluzione veloce, sono una grave minaccia per l’incolumità della popolazione, dei beni e delle infrastrutture del territorio che, in assenza di un sistema di allerta adeguato non possono essere salvaguardati. Lo studio e il monitoraggio di fenomeni franosi può essere realizzato a diverse scale e con diverse tecnologie, ma negli ultimi decenni le metodologie geofisiche sono state largamente utilizzate per questo scopo, grazie alla peculiarità di essere non invasive e di poter rilevare la variazione di parametri fisici in un volume di terreno. Per quanto riguarda le frane superficiali, analizzate in questo studio, uno dei fattori predisponenti per l’attivazione è l’apporto precipitativo, che va a determinare variazioni nel contenuto d’acqua del suolo e nella pressione interstiziale. Diversi ricercatori hanno constatato l’utilità di misure geoelettriche per la valutazione del contenuto idrico nel corpo di frane superficiali (Perrone et al., 2008; De Bari et al., 2011; Ravindran e Prabhu., 2012) e in alcuni casi è stato predisposto un sistema di monitoraggio in continuo (Supper et al., 2008; Kuras et al., 2009; Hilbich et al., 2011). L’obiettivo di questo studio è quello di valutare, partendo dalla sperimentazione di laboratorio, l’applicabilità di un monitoraggio geoelettrico nel riconoscimento di un livello soglia di contenuto d’acqua per l’instaurarsi dell’instabilità di una frana superficiale.

2017 - Sperimentazione di un sistema di monitoraggio geoelettrico permanente per la valutazione della stabilità arginale [Relazione in Atti di Convegno]
Tresoldi, Greta; Arosio, Diego; Hojat, Azadeh; Longoni, Laura; Papini, Monica; Zanzi, Luigi
abstract

Gli argini sono l’ultima difesa per salvaguardare le vite umane e i beni materiali dalla potenza distruttrice delle inondazioni. Sfortunatamente ad oggi in Italia non è prevista per legge una procedura sistematica e oggettiva di valutazione della stabilità degli argini. I consorzi di Bonifica, enti preposti alla manutenzione dei rilevati arginali, eseguono infatti ispezioni visuali delle strutture, operazioni soggettive che dipendono fortemente dall’operatore che realizza il sopralluogo. Negli ultimi decenni le metodologie geofisiche sono state utilizzate di frequente per valutare lo stato di salute dei rilevati in terra (Kim et al., 2007; Cardarelli et al., 2014) e in particolar modo la geoelettrica è stata utilizzata per il riconoscimento di zone di filtrazione preferenziale e per valutare la saturazione differenziale all’interno delle strutture (Takakura et al., 2013; Perri et al., 2014; Loperte et al., 2016). Solo in pochi casi, però, sono stati implementati sistemi di monitoraggio permanenti (Hilbich et al., 2011; Supper et al., 2011). L’obiettivo di questo lavoro è la valutazione della stabilità dei rilevati arginali in terra in tempo reale, in una maniera indiretta, economica e efficace, grazie all’implementazione di un monitoraggio geoelettrico per il riconoscimento di vie preferenziali di filtrazione e zone a contenuto d’acqua non omogeneo.

2017 - Understanding slope behavior through microseismic monitoring [Abstract in Atti di Convegno]
Arosio, Diego; Boccolari, Mauro; Longoni, Laura; Papini, Monica; Zanzi, Luigi
abstract

It is well known that microseismic activity originates as an elastic stress wave at locations where the material is mechanically unstable. Monitoring techniques focusing on this phenomenon have been studied for over seventy years and are now employed in a wide range of applications. As far as the study of unstable slope is concerned, microseismic monitoring can provide real-time information about fracture formation, propagation and coalescence and may be an appropriate solution to reduce the risk for human settlements when structural mitigation interventions (e.g., rock fall nets and ditches) cannot cope with large rock volumes and high kinetic energies. In this work we present the datasets collected in a 4-year period with a microseismic monitoring network deployed on an unstable rock face in Northern Italy. We mainly focus on the classification and the interpretation of collected signals with the final aim of identifying microseismic events related to the kinematic and dynamic behavior of the slope. We have analyzed signal parameters both in time and frequency domains, spectrograms, polarization of 3-component recordings supported by principal component analysis. Clustering methodologies have been tested in order to develop an automatic classification routine capable to isolate a cluster with most of the events related to slope behavior and to discard all disturbances. The network features both geophones and meteorological sensors so that we could also explore the correlation between microseismic events and meteorological datasets, although no significant relationships emerged. On the contrary, it was found that the majority of the events collected by the network are short-time high-frequency signals generated by electromagnetic activity caused by near and far thunderstorms. Finally, we attempted a preliminary localization of the most promising events according to an oversimplified homogeneous velocity model to get a rough indication about the regions of the monitored area that could be prone to collapse.

2016 - Fracture characterization with GPR: A comparative study [Relazione in Atti di Convegno]
Arosio, Diego; Deparis, J.; Zanzi, L.; Garambois, S.
abstract

Provided that the frequency of the GPR antenna is properly selected, detecting rock fractures is generally an achievable task because most of the investigated rocks are resistive. On the other hand, fractures can be generally envisaged as thin-beds embedded in a homogenous rock formation, thus yielding a complex reflection pattern caused by the reverberation of the GPR signal back and forth within the bed. As a result, dedicated approaches must be developed in order to extract quantitative information about fracture properties, i.e. thickness and permittivity of filling material, encoded in the thin-bed response. This work presents a comparison of two approaches for fracture characterization that we recently tested on synthetic, lab as well as field datasets. Although both approaches rely on amplitude and phase information in the frequency domain, their strategies significantly differ. The first one is based on common-offset data and involves deterministic deconvolution, while the second one processes common-midpoint reflections according to an amplitude-and-phase-variation-with-offset inversion. We test the performance of both approaches on a lab specimen scanned with high frequency antennas. Our aim is to identify shortcomings and advantages of the tested approaches, and to evaluate their outcomes according to the needs of possible field applications, in terms of acquisition time and accuracy.

2016 - GPR response to fractures with different filling materials [Abstract in Atti di Convegno]
Arosio, Diego; Zanzi, Luigi; Longoni, Laura; Papini, Monica
abstract

2016 - Multi Criteria Analysis supporting effective landslide modeling [Relazione in Atti di Convegno]
Longoni, Laura; Papini, Monica; Brambilla, Davide; Arosio, Diego
abstract

Numerical modeling may be an effective tool to predict the behavior of instable slopes provided that it relies on appropriate slope physical model. This is particular true for large-scale landslides, that generally feature intrinsic high spatial variability. For these large mass movements, it is crucial to assess the required spatial scale and input data accuracy for a correct numerical analysis of landslide. This paper investigates the role of the spatial scale and data accuracy in landslide modeling by considering as a testbed a Deep Seated Gravitational Slope Deformation (DSGSD) located in the North of Italy. Thanks to a large amount of available data, collected by means of geological and geophysical surveys, several numerical simulations with different resolutions (in term of geological and geomorphological settings) were performed. A comparison between the outcomes of the numerical models was accomplished through the use of a Multi Criteria Analysis (MCA) in order to evaluate landslide modeling with respect to numerical performance, investigations cost and time constraints. As a matter of fact, the high costs of detailed investigations often prevent an adequate slope assessment. Therefore, it is of primary importance to understand the role of input data on the effectiveness of numerical simulations. Hence, a decision support system capable to consider all these aspects is presented in order to define the best model as a trade-off between effectiveness, in terms of outcomes, and cost investigations.

2016 - Rock fracture characterization with GPR by means of deterministic deconvolution [Articolo su rivista]
Arosio, Diego
abstract

In this work I address GPR characterization of rock fracture parameters, namely thickness and filling material. Rock fractures can generally be considered as thin beds, i.e., two interfaces whose separation is smaller than the resolution limit dictated by the Rayleigh's criterion. The analysis of the amplitude of the thin bed response in the time domain might permit to estimate fracture features for arbitrarily thin beds, but it is difficult to achieve and could be applied only to favorable cases (i.e., when all factors affecting amplitude are identified and corrected for). Here I explore the possibility to estimate fracture thickness and filling in the frequency domain by means of GPR. After introducing some theoretical aspects of thin bed response, I simulate GPR data on sandstone blocks with air- and water-filled fractures of known thickness. On the basis of some simplifying assumptions, I propose a 4-step procedure in which deterministic deconvolution is used to retrieve the magnitude and phase of the thin bed response in the selected frequency band. After deconvolved curves are obtained, fracture thickness and filling are estimated by means of a fitting process, which presents higher sensitivity to fracture thickness. Results are encouraging and suggest that GPR could be a fast and effective tool to determine fracture parameters in non-destructive manner. Further GPR experiments in the lab are needed to test the proposed processing sequence and to validate the results obtained so far.

2016 - The risk of collapse in abandoned mine sites: The issue of data uncertainty [Articolo su rivista]
Longoni, Laura; Papini, Monica; Brambilla, Davide; Arosio, Diego; Zanzi, Luigi
abstract

Ground collapses over abandoned underground mines constitute a new environmental risk in the world. The high risk associated with subsurface voids, together with lack of knowledge of the geometric and geomechanical features of mining areas, makes abandoned underground mines one of the current challenges for countries with a long mining history. In this study, a stability analysis of Montevecchia marl mine is performed in order to validate a general approach that takes into account the poor local information and the variability of the input data. The collapse risk was evaluated through a numerical approach that, starting with some simplifying assumptions, is able to provide an overview of the collapse probability. The final results is an easy-accessible-transparent summary graph that shows the collapse probability. This approach may be useful for public administrators called upon to manage this environmental risk. The approach tries to simplify this complex problem in order to achieve a roughly risk assessment, but, since it relies on just a small amount of information, any final user should be aware that a comprehensive and detailed risk scenario can be generated only through more exhaustive investigations.

2016 - The role of the spatial scale and data accuracy on deep-seated gravitational slope deformation modeling: The Ronco landslide, Italy [Articolo su rivista]
Longoni, Laura; Papini, Monica; Brambilla, Davide; Arosio, Diego; Zanzi, Luigi
abstract

In recent decades numerical models have been developed and extensively used for landslide hazard and risk assessment. The reliability of the outcomes of these numerical simulations must be evaluated carefully as it mainly depends on the soundness of the physicalmodel of the landslide that in turn often requires the integration of several surface and subsurface surveys in order to achieve a satisfactory spatial resolution. Merging diverse sources of data may be particularly complex for large landslides, because of intrinsic heterogeneity and possible great data uncertainty. In this paper,we assess the spatial scale and data accuracy required for effective numerical landslide modeling. We focus on two particular aspects: the model extent and the accuracy of input datasets. The Ronco landslide, a deep-seated gravitational slope deformation (DSGSD) located in the North of Italy, was used as a test bed. Geological, geomorphological and geophysical data were combined and, as a result, eight models with different spatial scales and data accuracies were obtained. The models were used to run a back analysis of an event in 2002, during which part of the slope moved after intense rainfalls. The results point to the key role of a proper geomorphological zonation to properly set the model extent. The accuracy level of the input datasets should also be tuned. We suggest applying the approach presented here to other DSGSDs with different geological and geomorphological settings to test the reliability of our findings.

2016 - Water tunnels in mountain areas: Assessing the erosional activity with GPR [Relazione in Atti di Convegno]
Arosio, Diego; Ivanov, Vladislav Ivov; Zanzi, Luigi
abstract

Hydrogeological risk assessment regarding mountain rivers (both alpine and pre-alpine) must entail careful geological and hydraulic analyses about the interaction between water flow and man-made structures. This is not limited to dams and check-dams, but also include concrete tunnels that are often built to channel water flow into the underground in densely populated urban areas. Mountain streams generally feature small concentration time and significant solid transport that may pose a serious threat to the population. More in details, solid transport can cause diverse issues, including major alterations in the water flow regime, flooding and, in the worst cases, severe damages to structures. In this work we present a case study concerning the investigation of a concrete lined water tunnel located in the pre-alpine area in the North of Italy. We performed geophysical analysis by means of the Ground Penetrating Radar (GPR), a high-frequency electromagnetic technique able to investigate concrete structures in a non-destructive manner and with a good resolution. Our aim is to identify the erosional activity beneath the tunnel floor caused by water flow and the associated solid transport. The outcomes of this study can identify the damaged tunnel segments where repair interventions are most urgent.

2015 - Analysis of Microseismic Activity Within Unstable Rock Slopes [Relazione in Atti di Convegno]
Arosio, Diego; Longoni, Laura; Papini, Monica; Zanzi, Luigi
abstract

This chapter illustrates the concept of passive seismics as a method for monitoring the propagation of cracks within a rock mass as a result of load stress or water freezing in view of the use of this technique for rockfall early warning. The methodology is still far from being a standard and consolidated technique. The research is making progress, but just a few real case studies are documented. They are shortly overviewed in the introduction. Then, an interesting field test where crack propagation was artificially triggered up to full rock detachment, while a small sensor network was active, is discussed to show the existence and the characteristics of precursory signals. It follows the illustration of the microseismic monitoring methodology through the description of the Mt. San Martino (Lecco, Italy) sensor network and the discussion of the preliminary results obtained during the initial months of activity. Apparently, the preliminary results show some correlation with rainfalls, but not with temperature. Microseismic spectra are mainly concentrated in the first 100 Hz. This probably means that the hypocentre distances from the sensors are quite longer than 10 m. Electromagnetic interferences are also observed as mentioned by other authors who have analyzed data sets from other microseismic networks installed in mountain regions. They are automatically discriminated from significant signals by a classification software which works on the time/ frequency properties of these events. Hypocenter localization and clustering analysis of the significant events are the planned near- future activities.

2015 - Fracture thickness from GPR measurements [Relazione in Atti di Convegno]
Arosio, Diego; Zanzi, Luigi; Longoni, Laura; Papini, Monica
abstract

Rock investigation is definitely not a recent application of Ground Penetrating Radar (GPR) technique, as first studies date back to the seventies. However, only in the last decade research activities have started to address GPR characterization of rock fracture parameters, namely aperture and filling material. Rock fractures can generally be considered as thin beds, i.e., two interfaces whose distance is smaller than radar range resolution. Most of the past studies analyzed thin-bed response in the time domain, addressing time resolution, the linear relationship between bed thickness and reflected amplitude, and the derivative effect upon the incident signal. Amplitude calibration might permit to estimate fracture features for arbitrarily thin beds, but it is difficult to achieve and could be applied only to favorable cases. In this paper we explore the possibility to estimate fracture thickness and filling in the frequency domain by means of GPR. After reviewing the theoretical aspects of thin-bed response, we processed GPR data collected on ornamental marble blocks, where fractures of known aperture were simulated. We also performed numerical modelling tests to support the analysis of real datasets. Our approach consists of a 4-step procedure in which deterministic deconvolution is used to retrieve magnitude and phase thin-bed response in the selected frequency band. The procedure provided satisfactory outcomes when applied to real as well as to modelled thin-bed reflections. Results are encouraging and suggest that, under favorable circumstances, GPR could be a fast and effective tool to determine fracture parameters in non-destructive manner. Further testing is needed in order to fine-tune the processing sequence and to extend the validity of our preliminary findings to more complex case studies.

2015 - Microseismic monitoring of an unstable rock face - Preliminary signal classification [Relazione in Atti di Convegno]
Arosio, Diego; Zanzi, L.; Longoni, L.; Papini, M.
abstract

We analyse signals collected by a microseismic monitoring network installed on an unstable rock face threatening the city of Lecco, in the North of Italy. We propose a classification process based on parameters computed in both time and frequency domains able to identify events possibly related to microseismic activity within the unstable rock mass and discard unwanted signals caused by meteorological conditions or other sources of noise. Our classification routine seems to be robust and the preliminary outcomes are in agreement with the findings reported in previous studies. We believe that further investigations together with the integration with a localization process of the significant microseismic events will improve our approach.

2014 - A case study where dual-polarization was essential for correct interpretation of GPR results [Relazione in Atti di Convegno]
Arosio, Diego; Munda, Stefano; Zanzi, Luigi
abstract

The 19th century restoration works of the Basilica of Sant'Andrea in Mantua consisted of important modifications of pronaos and facade. According to historical documents, the use of metal reinforcements was planned to tie the facade with the counter-facade but designs and details are missing and since no external evidences of the tie-rods can be observed, the existence of these reinforcements was a fundamental open issue. The problem has been recently addressed with a GPR survey. Some tie-rods have been confirmed. The location of some of them has been problematic because of plaster decorations that reduced the survey area to narrow corridors. The dual-polarization was a benefit because some reinforcements, oriented parallel to the survey corridor, were detected only by the parallel-broadside polarization. In addition, for the exact location of these elements, 3D migration was needed because the reflection was generated out-of-plane. Some other unexpected reinforcements were also detected within the counter-facade wall. The complex geometry of these reinforcements was finally understood by composing the results of GPR investigations on orthogonal faces of the counter-facade. However, a tricky question arose on one side of the wall where an unexpected anomaly in GPR response seemed to reveal the presence of an additional set of metal bars. Again the dual-polarization was essential to exclude this misinterpretation and to understand the real origin of these unexpected signals.

2014 - A new geological model for Spriana landslide [Articolo su rivista]
Longoni, L; Papini, M.; Arosio, Diego; Zanzi, L.; Brambilla, D.
abstract

Complex large landslides are characterized by different kinematic behaviors and involve diverse materials. Both elements make it difficult to study the instability of these huge mass movements, which may cause massive damage and affect extended areas. This paper is focused on the study of Spriana landslide, an important rockslide located in the North of Italy. Starting from the geological interpretation provided by Belloni and Gandolfo (Geologia tecnica ed ambientale 3:7–36, 1997), the authors gather all available data sets and perform a novel analysis aimed to better describe the unstable body. The key point of this case study regards the characterization of the deeper surface of failure. The location as well as the continuity of this surface is a crucial unsolved question, and in this paper we try to provide a reasonable answer. We propose a new hypothesis based on a structurally controlled, wedge-like rockslide involving the presence of a composed deeper surface of failure constrained by the intersection of two different weak zones. Although this work mainly addresses the development of a new geological model, numerical simulations were also performed. Both continuous and discontinuous models were tested, and then a comparison of the outcomes of the numerical simulations was performed to define the best fit to the observed landslide behavior.

2013 - Freeze-thaw cycle and rockfall monitoring [Relazione in Atti di Convegno]
Arosio, Diego; Longoni, Laura; Mazza, Fabrizio; Papini, Monica; Zanzi, Luigi
abstract

Among several weathering processes that may contribute to rock fall generation, a particular issue is related to freeze-thaw cycles. Several studies claimthatmany rock falls originate from thawing of the fractured bedrock during seasonal freezing (Matsuoka and Marton Permafrost Periglac Process 19(2):195-210, 2008; Matsuoka Cold Reg Scid Technol 17(3):253-270, 1990). Other authors have recently suggested that ice segregation is the real cause behind bedrock fracturing (Hallet Science 314(5802):1092-1093, 2006; Murton et al. Permafrost Periglac Process 12(3):255-266, 2001, Science 314(5802):1127-1129, 2006). Consequently, freeze and thaw processes will be deeply investigated in order to discover possible relationships between triggering mechanisms concerning rockfalls and monitoring datasets. Laboratory tests have been carried out to investigate the rupture process caused by the abovementioned cycles. Preliminary analyses were performed both in lab and on the field with the aim of testing the capability of different transducers to register micro seismic signals. © Springer-Verlag Berlin Heidelberg 2013.

2013 - GPR investigations of rock fractures: Considerations on thin beds [Relazione in Atti di Convegno]
Arosio, Diego; Zanzi, Luigi; Longoni, Laura; Papini, Monica
abstract

Detection of fractures within resistive rock masses is at present a very Common application of Ground Penetrating Radar (GPR) technique. GPR investigations have been performed in several mines and quarries, as well as over unstable rock slopes. The detection and location of fractures is obviously of great importance for safety reasons but can also be used, for instance by the quarrying industry, to improve the production of ornamental rock slabs. According to the desired trade-off between resolution and penetration depth, the full frequency range of Commercial GPR systems (from tens of MHz to few GHz) has been employed in these investigations. In most cases rock fractures can be considered as beds whose thickness is smaller than the resolution limit (i.e., a thin bed), and can be envisaged as layers embedded in a homogeneous formation, giving rise to reflected signals from the top and the bottom of the bed having opposite polarities. Studies on reflections from thin beds have been carried out by the seismic industry for nearly sixty years now and new developments are still underway. In the last decade, the GPR Community has focused on thin beds response to determine rock fracture features (aperture and filling material). In our work we attempt to review the fundamentals of thin bed response, mainly addressing the relationship between the thickness of the bed and the time and frequency characteristics of the reflected wavelet. Then we consider GPR numerical simulations and experiments performed with a high frequency antenna on quarried marble blocks to compare analytical expressions of thin bed response to synthetic and real GPR datasets.

2013 - New investigations to update the model of the Premana (LC) landslide [Relazione in Atti di Convegno]
Arosio, Diego; Brambilla, Davide; Longoni, Laura; Papini, Monica; Zanzi, Luigi
abstract

Deep seated landslides have historically caused extensive damage to land and structures. These large failures are usually controlled by several triggering factors, and one of the most important is deemed to be the change in pore-water pressure inside the slope. To define the 3D geological model of complex landslides an integrated approach which combines the results of surface and subsurface surveys is often mandatory. This paper aims to present the integrated approach adopted to study the Premana landslide, a deep seated landslide in the North of Italy. The outputs of the geophysical surveys have been combined with geological observations and have been used to model slope stability related to different water table levels in order to define the critical thresholds of pore-water pressure. Considering the complexity of the landslide, the heterogeneity of the geological features and the limitations inherent to each methodology, different approaches were used to study the Premana landslide. © Springer-Verlag Berlin Heidelberg 2013.

2013 - Seismic characterization of an abandoned mine site [Articolo su rivista]
Arosio, Diego; Longoni, Laura; Papini, Monica; Zanzi, Luigi
abstract

The near-surface rock structure that covers an abandoned marl mine nearby the village of Montevecchia (Italy) was investigated through a combination of seismic surveys. The methods selected for these investigations were refraction seismics and multichannel analysis of surface waves (MASW). A sort of transillumination experiment was also attempted. All the methods were successful and gave complementary information. Refraction seismics was used to characterize the upper low velocity layer and the second layer of the near-surface structure. The MASW method was necessary to assess the existence of a velocity inversion revealing the presence of a low velocity layer between the 2nd layer and a 4th high velocity layer covering the upper mine gallery. The transillumination experiment validated the presence of the 4th layer and gave an estimate of the average velocity that represents a lower boundary for the P-wave velocity within this layer. Both the refraction and transillumination data were analysed to derive average estimates of attenuation level and rock quality factor. © 2012 Versita Warsaw and Springer-Verlag Wien.

2013 - Sensitivity and accuracy in rebar diameter measurements from dual-polarized GPR data [Articolo su rivista]
Zanzi, Luigi; Arosio, Diego
abstract

According to some authors, high-frequency GPR (Ground Penetrating Radar) can provide on-site non-destructive measurements of the diameter of concrete reinforcements. The procedure should be based on the analysis of radar energy scattered by reinforcements when illuminated with parallel and perpendicular polarization. The theory of Radar Cross Section (RCS) supports this assumption. However, laboratory test performed on concrete specimens indicate that many practical problems must be solved to obtain reliable and stable measurements from real data. Synthetic data were used to analyze the problem. A data processing sequence was optimized to obtain the best fit between synthetic results and theoretical expectations. Results on real data processed with the same sequence were less encouraging. The comparison with synthetic data was essential to understand that background subtraction is the most critical issue. This problem is of larger importance than the fact that commercial GPR systems generate wide band radar pulses while RCS theory is frequency dependent. Once identified, the problem was directly addressed and results improved significantly. Although delicate, the methodology is potentially showing a high sensitivity which is proportional to wavelength. An optimal selection of antenna frequency versus rebar diameter range is proposed to preserve the highest sensitivity. Accuracy is related with sensitivity but also with stability and repeatability of the measurements. On-site experiments performed to explore this issue suggest that the problem must be addressed statistically. This makes the procedure more complex but the use of dual-polarized antennas might be the solution to save efficiency and cost-effectiveness. © 2012 Elsevier B.V. All rights reserved.

2013 - The residual risk of an abandoned mine [Relazione in Atti di Convegno]
Brambilla, D; Longoni, L; Papini, M; Arosio, Diego; Zanzi, L.
abstract

It is well known that the mine legacy is a serious concern to present communities. The high risk associated with subsurface voids together with the lack of knowledge of geometric and geomechanical features of former mining areas make abandoned underground mines one of the current challenges for countries with a long mining history. In Italy, no long-term assessment of abandoned mine sites is required by law. In this paper we deal with the case study of Montevecchia mine, a marl mine in northern Italy abandoned in 1958 after a massive collapse. The event affected all mine levels along their middle sections and caused a large sinkhole. We initially performed geological and geophysical investigations to develop a physical model of the site. After that we carried out several numerical simulations to evaluate the stability of tunnels still in place.

2013 - The role of shear surface geometry in the definition of deep-seated gravitational slope deformation thresholds [Relazione in Atti di Convegno]
Brambilla, D; Longoni, L; Papini, M; Arosio, Diego; Zanzi, L.
abstract

Deep-Seated Gravitational Slope Deformations (DSGSD) often involve complex kinematic behaviors that may vary spatially and temporally. The Alpine area counts several DSGSDs involving volumes of millions of cubic meters. In this paper we present the case study of Spriana landslide, a common example of DSGSD located in the North of Italy. Geological, geophysical and topographic investigations have been combined to develop an accurate physical model of the slope. However, some issues still need to be tackled and the definition of a reliable triggering threshold is yet a challenge. Our work focuses on the importance of the shear surface geometric features for threshold definition. We performed several 3D numerical simulations addressing the definition of groundwater table critical level. We believe our findings may improve the early warning system of Spriana landslide and we think that our approach should be used to address other complex deep seated gravitational slope deformations.

2012 - GPR investigations to assess the state of damage of a concrete water tunnel [Articolo su rivista]
Arosio, Diego; Munda, Stefano; Zanzi, Luigi; Longoni, Laura; Papini, Monica
abstract

Erosional voids developing around concrete-lined tunnels can compromise the safety of the surrounding areas, as well as of the tunnels themselves. In this study, ground penetrating radar (GPR) was used to assess the condition of a water tunnel built to channel a river under a mountain road. The tunnel is lined with 60-80 cm thick concrete and has a semicircular crosssection with a diameter that varies between 3 m and 4 m. The concrete structure has been damaged from erosion beneath the concrete floor, creating a sequence of pools and waterfalls, which further extend the erosive action below the floor and side walls.

2012 - Nondestructive Quality Control of Reinforced Masonry Buildings [Articolo su rivista]
Arosio, Diego; Munda, Stefano; Zanzi, Luigi; Porto, Francesca da; Mosele, Flavio
abstract

In the framework of the DISWall research project, funded by the European Commission, the authors have been working on the development of quality-assessment procedures for modern reinforced masonry buildings based on nondestructive testing methods. Two specific types of reinforced masonry systems were considered, both based on concentrated vertical reinforcements and on the use of perforated clay units. This contribution focuses on results obtained by radar and sonic techniques. They were applied in the laboratory on two masonry specimens, which were built with known defects. Tests were also carried out on-site, on real walls of a selected case study. On the basis of the results of these experiments, a fully nondestructive quality-control procedure appears feasible and promising. The data can be collected and analyzed in real time with an automatic classification algorithm. The procedure requires the use of a high-frequency GPR (ground-penetrating radar) system. Depending on the type of masonry system, sonic test equipment might also be required to investigate some specific problems that cannot be diagnosed by the GPR. Feedback from the building sector is now essential to understand the interest in and the potential market for this nondestructive testing application. As a result, new investments could be planned to perform the further testing activities that are needed to standardize the procedure. © 2012 American Society of Civil Engineers.

2012 - Preliminary seismic survey on the unstable slope of Madesimo (Northern Italy) [Relazione in Atti di Convegno]
Apuani, Tiziana; Arosio, Diego; De Finis, Erika; Stucchi, Eusebio; Zanzi, Luigi; Ribolini, Adriano
abstract

Diverse non-invasive seismic techniques are used to gain a fundamental knowledge of a complex unstable slope in the Italian Central Alps. A recent detailed geomorphological survey has proved the slope is affected by a deep gravitational deformation accompanied by superficial landslide phenomena, debris avalanches, soil creep and infrastructure damages. As the unstable slope directly threatens the popular ski resort of Madesimo, the risk associated to a possible collapse may be very high. Hence new efforts are required to define the geological and physical model of the slope, and to comprehend its dynamic and cinematic behavior. Recently, preliminary 2D seismic investigations have been carried out at the slope toe, where a supposed sliding surface can be more easily detected, the slope is more gentle and a road offers the possibility to bring the seismic equipment close to the survey line. A shotgun and a 72-channel system assembled by combining equipment from two different manufacturers have been used to perform a reflection/refraction survey. P-wave first arrivals have been inverted with the main purpose of delineating the interfaces between weathered and massive rock and the velocity gradients associated with different fracturing degrees of the rock slope. The same dataset has been also processed according to the Multi-channel Analysis of Surface Waves (MASW) methodology. Surface wave analysis has been used to characterize the slope with S-waves, thus providing complementary information with respect to the refraction survey, as well as to verify the presence of velocity inversions. Reflection data have been processed to better identify the acoustic discontinuities within the slope and to extend the penetration depth of the previous seismic techniques. The processing sequence involves basic steps with no multichannel operations to avoid introducing artifacts in the seismic section. Seismic results have been jointly interpreted with the support of the geological information gathered by superficial surveys.

2012 - Quality control of stone blocks during quarrying activities [Relazione in Atti di Convegno]
Arosio, Diego; Munda, Stefano; Zanzi, Luigi
abstract

Early detection of fractures and internal defects can help quarry owners in cutting quarrying costs and reducing the amount of waste products. Valuable stones used in construction industry such as marble, porphyry, granite, travertine, are usually extracted from quarries by cutting blocks whose size normally varies between 5 and 15 m 3. Transportation of these blocks from quarries, often located at high altitudes in mountainous environments, down to the headquarters of the stone industry where big machines are installed to transform the big size blocks into slabs or small size stones, can be quite expensive. Money could be saved by checking on-site the big size blocks with NDT methods able to detect internal fractures and other defects (voids, clay inclusions, etc.). A detailed map of fracture extension and orientation can be also very profitable in optimizing the production line. For example, the final destination of a block (i.e., production of slabs rather than small size blocks or other) and the orientation of the cutting planes can be more properly assigned. Currently, Ground Penetrating Radar is the most promising method for this type of application. It can be applied on-site, it can generate high resolution 3D reconstructions of fractures and defects, quasi-real-time results are feasible. Thus, it can be a cost-effective tool, worth being introduced into the quarry industry. To evaluate the potential of this technology for the quarry industry we have been testing the method on marble and porphyry blocks from a couple of quarries belonging to the Brescia stone district (North Italy). Results are very encouraging: all type of defects and fractures that might have an impact on the production line can be detected by 3D surveying the block with a 2GHz GPR system. A dual-polarized antenna is a plus that makes acquisitions faster and easier. Data processing must include two-dimensional filtering to cancel the artifacts generated by side reflections and 3D migration to generate accurate reconstructions of the target geometries. ©2012 IEEE.

2012 - Shallow seismic investigations of an abandoned mine [Relazione in Atti di Convegno]
Arosio, Diego; Zanzi, L.; Longoni, L.; Papini, M.
abstract

The near-surface rock structure that covers an abandoned marl mine nearby the village of Montevecchia (Italy) was investigated through a combination of seismic surveys performed in two different survey campaigns. The methods selected for these investigations were Refraction Seismics and Multichannel Analysis of Surface Waves (MASW). A sort of transillumination experiment was also attempted. All the methods were successful and gave complementary information. Refraction seismics was used to characterize the shallower low velocity layers and a deeper high velocity layer of the near-surface structure. The MASW method was necessary to assess the existence of a velocity inversion revealing the presence of a low velocity layer between the faster layer identified by refraction seismics and a 4th high velocity layer covering the upper mine gallery. The transillumination experiment validated the presence of the 4th layer and gave an estimate of the average velocity that represents a lower boundary for the P-wave velocity within this layer. Both refraction and transillumination data were analysed to derive average estimates of attenuation level and rock quality factor.

2012 - Surface and subsurface non-invasive investigations to improve the characterization of a fractured rock mass [Articolo su rivista]
Longoni, L; Arosio, Diego; Scaioni, M.; Papini, M.; Zanzi, L.; Roncella, R.; Brambilla, D.
abstract

Three-dimensional assessment and modelling of fractured rock slopes is a challenging task. The reliability of the fracture network definition is of paramount importance for several engineering and geotechnical applications, and so far, different approaches have been proposed to improve the assessment procedure. A thorough knowledge of the actual fracture system is necessary to construct an accurate geometrical model of the rock mass and to determine block size distribution within the rock body. This paper describes the integration of diverse techniques used to define the rock mass fracture pattern, focusing on the most important fracture features, which are joint orientation, spacing, and persistence. A case study in the north of Italy was selected in order to show the potential of an integrated approach where surface and subsurface investigations are coupled. The rock surface was analysed by means of both standard geological mapping and terrestrial laser scanning. Ground penetrating radar surveys were conducted to image and map the discontinuity planes inside the rock mass and to estimate fracture persistence. The results obtained from the various investigation methodologies were employed to construct a model of the rock mass. This approach may lead to a better understanding of fracture network features, usually observed only on the rock surface. A careful analysis of block size distribution in a rock body can be of valuable help in several engineering and risk mitigation applications. © 2012 Sinopec Geophysical Research Institute.

2010 - A microseismic approach to locate survivors trapped under rubble [Articolo su rivista]
Arosio, Diego
abstract

The detection of microseismic noise generated by survivors trapped by debris is a method already used by Search and Rescue (S&R) teams. Present seismic S&R equipment works exclusively on energy analysis whilst ignoring information associated with propagation delays. We explore the potential of using traveltime analysis compared to energy analysis for both 2D and 3D location. Results obtained from three different debris field scenarios used for training S&R teams demonstrate that using travel-time information is more reliable than using energy information alone. A joint analysis of both signal parameters is suggested as an appropriate strategy to improve the reliability of locating survivors. Traveltimes can also potentially extend the location into the third dimension by returning an approximate estimate of the survivor depth below ground level. The main obstacles to achieving this goal are the inhomogeneity of the debris pile, the need for a real-time response and the limited spatial extension of the sensor array. Despite these difficulties, results obtained in the field, with an algorithm based on energy focusing by means of cross-correlation and semblance operators, show an accuracy within the limit of the seismic resolution. A new searching strategy is defined and the procedure reduces the investigation time taken by current seismic S&R systems by a factor of three. © 2010 European Association of Geoscientists & Engineers.

2010 - Predicting slope collapse using Slope Stability Radar deformation data [Relazione in Atti di Convegno]
Arosio, Diego; Harries, N.
abstract

We selected six open-pit wall collapses, representing a variety of failure sizes, failure types and rock mass characteristics, in order to assess the accelerating creep theory by Voight and Fukuzono as an early forecasting tool. Time-displacement monitoring data were collected shortly before ultimate failure using the GroundProbe Slope Stability Radar (SSR), a ground based interferometric radar able to detect surface displacements with a sub-millimetre accuracy. Non-linear estimation techniques were employed to relate slope displacement behaviours to Voight's empirical relationship in order to investigate the trend of its controlling parameters and possibly identify a time window where forecasting output were found to be stable. Analyses were performed taking into account different amounts of survey points involved in the failure mechanism and various values of the velocity at time of failure parameter. Finally we evaluated Fukuzono's inverse velocity approach paying particular attention to update linear fits whenever a trend change was identified. © 2010 Taylor & Francis Group, London.

2009 - A challenging gpr investigation to assess the state of damage of a water tunnel [Relazione in Atti di Convegno]
Munda, Stefano; Zanzi, Luigi; Arosio, Diego
abstract

The GPR method was used to assess the conditions of a water tunnel built to force a river to underpass the road running along the Valganna valley, 60km north of Milan (Italy). The tunnel is concrete lined and has a semicircular section with a diameter that varies between 3 and 4m. The most damaged section of the tunnel runs parallel to the valley for about 300m before intersecting the road where the valley makes a pronounced left turn. The concrete structure is severely damaged because water erosion of the concrete floor has been creating a sequence of pools and waterfalls extending the erosive action below the lateral walls. Large fractures visibly affect the concrete ceiling especially where the water has eroded the floor and the soil below the wall shoulders. As a result, the risk of tunnel failure is really high and, after a partial collapse, a GPR investigation was planned to assess the extent of the erosive action behind the walls and below the concrete floor. Most of the GPR measurements had to be performed from inside the tunnel. The late summer was chosen to operate with a reduced rate of water flow. Here we discuss surveying method and data interpretation.

2009 - Geophysics and caving: An example from the apuan alps [Relazione in Atti di Convegno]
Arosio, Diego; Garanzini, Stefano; Zanzi, Luigi
abstract

Seismic techniques were used to locate an underground cave in the Apuan Alps, world-famous marble mountains within a regional natural park in Tuscany, central Italy. Cavers have recently discovered a very long as well as intricate passageway in the subsurface ending in huge and spectacular natural cavities. Since the initial part of the path involves climbing, crawling and an extensive knowledge of caving techniques, it is accessible only to well-trained and athletic cavers. In order to make it feasible for a larger audience, it would be helpful to find a way from the surface intersecting the tunnel not far from the big voids. Previous attempts of the speleologists to dig a passage where the cave is believed to be shallower along with GPR investigations were unsuccessful. We initially performed a seismic refraction survey to characterize the site in terms of seismic velocities and layer thicknesses. Subsequently, seismic events were generated with a hammer inside the cave. The signals were collected on the surface along two orthogonal spreads. A radio-triggering system was attempted. Localization of source points was affected by unfavorable propagation conditions and involved signal analysis in terms of arrival time, energy and waveform.

2009 - Localization algorithms for search and rescue applications [Relazione in Atti di Convegno]
Arosio, Diego; Bernasconi, G.; Mazzucchelli, P.; Rovetta, D.; Zanzi, L.
abstract

Detection of microseismic noise generated by survivors trapped by debris is a method already used by S&R teams. Present S&R equipment work exclusively on energy analysis while ignore information carried by propagation delays. We explore the potential of traveltime analysis compared to energy analysis for 2D and 3D localization. Results obtained on a couple of debris fields used for training S&R teams demonstrate that traveltimes are not less reliable than energy. A joint analysis of both the signal parameters can be an appropriate strategy to improve the 2D localization reliability. Besides, traveltimes can potentially extend the localization to the third dimension by returning an approximate estimate of the survivor depth. Main obstacles to achieve this goal are the inhomogeneity of the debris pile, the need of a real-time response, the limited extension of the sensor array. Despite of these difficulties, the preliminary results obtained in the fields with two different algorithms, one based on statistical traveltime inversion, the other based on data focusing, are encouraging and show accuracy in the limit of the seismic resolution. Both the algorithms are flexible and can be customized to face the peculiar constraints posed by this application.

2009 - Towards rockfall forecasting through observing deformations and listening to microseismic emissions [Articolo su rivista]
Arosio, Diego; Longoni, L; Papini, M.; Scaioni, M.; Zanzi, L.; Alba, M.
abstract

Reliable forecasting of rockfall is a challenging task, mainly because of the lack of clearly noticeable forerunners as well as due to the geological and geo-mechanical complexity of the rock movements involved. Conventional investigation devices still present some drawbacks, since most measurements are generally carried out at isolated locations as well as on the surface only. Novel remote-sensing monitoring instruments, such as Terrestrial Laser Scanning (TLS) and Ground-Based Interferometric Synthetic Aperture Radars (GB-InSAR), are capable of inspecting an unstable slope with a high spatial and temporal frequency. But they still rely on measurements of the failure surface, from which displacement or velocity are measured. On the contrary, acoustic emission/microseismic monitoring may provide a deeper insight of stress and strain conditions within the subsurface rock mass. In fact, the capability to detect microseismic events originating within an unstable rock mass is a key element in locating growing cracks and, as a consequence, in understanding the slide kinematics and triggering mechanisms of future collapses. Thus, a monitoring approach based on the combination of classical methodologies, remote sensing techniques and microseismic investigations would be a promising research field. In the present paper we discuss the technologies and we illustrate some experiments conducted in the framework of a project whose final goal is the installation of an integrated monitoring and alerting system on a rockface nearby Lecco (Italy). In particular, we present a review of performances and applications of remote sensing devices and some results concerning a terrestrial laser scanner preliminary campaign. Then, we report findings regarding amplitude, frequency content and rate of signals recorded during an in situ test carried out to evaluate the performance of three different microseismic transducers. © Author(s) 2009.