131,195 research outputs found
Optimal Design for Expanding a Microseismic Monitoring Network on an Unstable Rock Face in Northern Italy
No full textMicroseismic 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
The role of shear surface geometry in the definition of deep-seated gravitational slope deformation thresholds
No full textDeep-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
The residual risk of an abandoned mine
No full textIt 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
Seismic Noise Azimuthal Spectral Ratios to Monitor Landslide Kinematics
No full textIn this work, we explore the potential of seismic noise as a monitoring tool for landslide kinematic behavior. We monitored an earth slide with low-frequency seismometers and we collected ambient vibrations during two following stages characterized by different displacement rates and stress states of the involved media. Spectral ratios between signals collected on the sliding body and at stable locations suggest that polarization of seismic noise in the azimuthal plane is sensitive to the direction of joint sets and deformation areas created by slope accelerations and differential movements. As a consequence, the analysis of seismic noise polarization could be of valuable help for monitoring the landslide kinematics
Centimetric Accuracy in GPR Measurements of Column and Capital Connecting Rebars
No full textIn this paper we discuss the application of ground penetrating radar (GPR) method in exploring the metallic reinforcement elements in masonry structures, addressing the precision challenges inherent in structural assessments. Selecting the proper frequency of the antenna is critical to achieve the desired centimetric accuracy in such surveys. We present the results of structural assessment surveys on a historical column using a 3GHz antenna that emerges as an effective compromise between the precision and the penetration. We propose a three-step calibration procedure that improves analysis of the data and provides reasonable results. We applied the proposed strategy to estimate the diameter of the rebars connecting the studied column to its base as well as to the capitals. Moreover, we could determine the penetration lengths of rebars inside the column. Our study illustrates the precision of the GPR method for non-destructive evaluations of historical structures, emphasizing the importance of careful calibration for achieving reliable and accurate results
Water tunnels in mountain areas: Assessing the erosional activity with GPR
No full textHydrogeological 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
Designing the expanded microseismic monitoring network for an unstable rock face in Northern Italy
No full textThe 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
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