Acoustic module of the Acquabona (Italy) debris flow monitoring system

International audienceMonitoring of debris flows aimed to the assessment of their physical parameters is very important both for theoretical and practical purposes. Peak discharge and total volume of debris flows are crucial for designing effective countermeasures in many populated mountain areas where losses of lives and property damage could be avoided. This study quantifies the relationship between flow depth, acoustic amplitude of debris flow induced ground vibrations and front velocity in the experimental catchment of Acquabona, Eastern Dolomites, Italy. The analysis of data brought about the results described in the following. Debris flow depth and amplitude of the flow-induced ground vibrations show a good positive correlation. Estimation of both mean front velocity and peak discharge can be simply obtained monitoring the ground vibrations, through geophones installed close to the flow channel; the total volume of debris flow can be so directly estimated from the integral of the ground vibrations using a regression line. The application of acoustic technique to debris flow monitoring seems to be of the outmost relevance in risk reduction policies and in the correct management of the territory. Moreover this estimation is possible in other catchments producing debris flows of similar characteristics by means of their acoustic characterisation through quick and simple field tests (Standard Penetration Tests and seismic refraction surveys)

Situazioni ambientali: una frana a Cortina d’Ampezzo

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An experiment on a sand-dune environment in Southern Venetian coast based on GPR, VES and documentary evidence

The internal structures of some surviving sand dunes and the ancient shore-lines along the coast south of Venice have been investigated integrating Ground Probing Radar (GPR) profiles, Vertical Electrical Soundings (VES) and water conductivity measurements in some boreholes. The GPR penetration depth has been limited (4-5 m,using a 400 MHz antenna) by the high conductivity of salt water saturating pores of the shallow sediments. On the other hand, the excellent spatial resolution of the radar survey provided an estimate of internal dune bedding features, such as cross lamination and forwarding ancient covered coast-lines dated in the Thirties. The interpretation of the data, in particular along one line 360 m long intercepting a sizable sand-dune bank, seems to offer clues to the evolutional history of the coast line and the depth of transition from fresh-water to brackish-salt water. The water table was detected with electrical measurements and direct observations in boreholes, whereas the transition between fresh and salt water (brackish water) was pointed out indirectly by the high energy absorption and total back-reflection of the EM waves, encountered at this boundary, and directly by the strong decrease in VES resistivity values

grid_strain and grid_strain3: software packages for strain field computation in 2D and 3D environment

Two MatlabTM software packages for strain field computation, starting from displacements of experimental points (EPs), are here presented. In particular, grid_strain estimates the strain on the nodes of a regular planar grid, whereas grid_strain3 operates on the points of a digital terrain model (DTM). In both cases, the computations are performed in a modified least square approach, emphasizing the effects of nearest points. This approach allows users to operate at different scales of analysis by introducing a scale factor to reduce or also exclude too far points from grid nodes. The input data are displacements (or velocities) that can be provided by several techniques (e.g. GPS, total topographical station, terrestrial laser scanner). The analysis can be applied to both regional- and local-scale phenomena, to study tectonic crustal deformations or rapid landslide collapses, and to characterize the kinematics of the studied system. Errors on strains and geometric significance of the results are also provided

First Italian TRT database and significance of the geological setting evaluation in borehole heat exchanger sizing

The correct sizing of the borehole field in closed-loop Ground Source Heat Pump (GSHP) systems requires accurate value of the ground thermal properties, especially the thermal conductivity. One of two methods are generally applied to evaluate this parameter: the Thermal Response Test (TRT) and databases reported in guidelines or Standards for lithologies identified in the local stratigraphy. This paper presents a database of more than 100 Thermal Response Tests performed in Italy. The equivalent thermal conductivities derived from the TRT outputs are here directly compared with the value estimated through knowledge of the local geological stratigraphy. The obtained results are analyzed in terms of geological setting. A sensitivity analysis on the borefield design has been conducted to evaluate the effects of the equivalent thermal conductivity estimation error on the calculation of the required total borehole length. The borehole length, in turn, strongly affects the initial investment costs as well as the operating conditions of the heat pump over the long term. The obtained results, in some cases significant, highlight the importance of performing the TRT not only when the thermal capacity of the GSHP is high but also in the case of strong geological uncertainty, or in particular geological settings such as high plain areas, alpine valley floors and rocky environments. In the other cases as low plain areas, this database can provide an initial estimate of the range of the expected equivalent thermal conductivity value; therefore, it can be useful for designers of both GSHP systems and other applications where the knowledge of the underground thermal behavior is necessary

Grid_strain and grid_strain3: Software packages for strain field computation in 2D and 3D environments

Two Matlab\u2122 software packages for strain field computation, starting from displacements of experimental points (EPs), are here presented. In particular, grid_strain estimates the strain on the nodes of a regular planar grid, whereas grid_strain3 operates on the points of a digital terrain model (DTM). In both cases, the computations are performed in a modified least-square approach, emphasizing the effects of nearest points. This approach allows users to operate at different scales of analysis by introducing a scale factor to reduce or also exclude points too far from grid nodes. The input data are displacements (or velocities) that can be provided by several techniques (e.g. GPS, total topographical station, terrestrial laser scanner). The analysis can be applied to both regional- and local-scale phenomena, to study tectonic crustal deformations (strain 4810 128 1210 126) or rapid landslide collapses (10 124 12102), and to characterize the kinematics of the studied system. Errors on strains and geometric significance of the results are also provided

Geotechnical Hazards Caused by Freezing-Thawing Processes Induced by Borehole Heat Exchangers

In closed-loop Ground Source Heat Pump system (GSHP), the thermal exchange with the underground is provided by a heat-carrier fluid circulating into the probes. In order to improve the heat extraction rate during winter, the heat-carrier fluid temperature is often lowered down to 125 \ub0C; this way, the induced thermal anomaly is more intense and can cause freezing processes in the surrounding ground. In sediments with significant clay fraction, the inner structure and the porosity distribution are irreversibly altered by freezing-thawing cycles; therefore, the geotechnical properties (such as deformability, stiffness and permeability) are significantly affected. A wide laboratory program has been performed in order to measure the induced deformations and the permeability variations under different conditions of thermal and mechanical loads and interstitial water salinity. The results suggest that, despite the induced frozen condition is quite confined close to the borehole, the compaction induced in cohesive layers is significant and irreversible and could generate negative friction on the borehole heat exchanger; in addition, the permeability increase in the probe surroundings could lead interconnection among aquifers, with increasing effects with the number of boreholes in the borefield