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Seismic characterization of an Alpine site

Site amplification of earthquake ground motion can arise from local stratigraphic and morphological nconditions. In this respect, a detailed geo-mechanical 2D model is needed, in particular for peculiar situations such as the ones in Alpine valleys. This paper reports a site characterization case history for seismic response analysis, where a combination of both body and surface wave seismic techniques has been used. In particular, it is shown that synergies and mutual cross-checking of information lead to a reliable 2D model for site amplification studies. nThe evaluation of the deep structure and the location of the seismic bedrock have been obtained through seismic reflection and combined active-passive surface wave analysis, while the shear-wave velocity profile of the sediments has been obtained by downhole measurements and surface wave tests. Furthermore, a detailed compressional wave velocity model has been retrieved by tomographic ninversion of the first arrivals picked on seismic reflection records. This model is useful for geological interpretation as well as for quality control of the other methods. Surface wave analysis has also been performed on the ground roll of the seismic reflection records. The large amount of profile oriented data has made it possible to reconstruct lateral variations of the shear-wave velocity nin the soil deposit. The final pseudo-2D shear-wave velocity model is the product of an innovative ninversion approach, based on the integration of the Monte Carlo and laterally constrained least-squares techniques. In the laterally constrained inversion the shear-wave velocity profiles obtained from downhole tests and data from passive surface wave measurements have been used to constrain the inversion. This has greatly improved the final solution. nThis case history underlines the necessity of combining different seismic techniques to derive an accurate and reliable 2D model for site amplification studies. Through several different and independent nanalyses of the same seismic records, the cost effectiveness of the whole survey is optimized and a full exploitation of the information contained in the reflection seismic data set is achieved.

EIT Oedometer: An Advanced Cell to Monitor Spatial and Time Variability in Soil with Electrical and Seismic Measurements

The paper presents an innovative oedometer cell (EIT oedometer), accomplishing for monitoring the spatial and temporal evolution of different physical quantities inside soil samples through seismic and electric non-destructive measurements. The technical solutions implemented to perform correct electrical measurements are reported together with the results of benchmark tests demonstrating the potentialities and the limits of the 3D electrical resistivity tomography in detecting both pre-existing and induced sample heterogeneities. It is shown that resistivity imaging can offer a powerful tool for the investigation of soil heterogeneities not detected by external measurements. The relationship between electrical resistivity and soil properties makes this application potentially useful for monitoring the evolution of transient processes as for instance those related to the diffusion of chemical species in clay soils and associated coupled chemo-mechanical processes, whereas the information gathered by classical oedometer measurements and by seismic waves propagation could be used to explore the associated macroscopic phenomena.

Effectiveness of geophysical surveys for water wells relocation in overexploited aquifers (the example of Maggiore and Traversola Valleys, Northwestern Italy)

Aquifer overexploitation is a common problem in drinking water management. This will become more and more important given the general reduction of water resources. To overcome overexploitation, one of the most adopted solutions is the relocation of extraction wells. To establish the positions of new wells, a precise knowledge of the hydrogeological setting is required. Specific surveys are therefore necessary to obtain information over wide investigation zones. Geophysical methods, particularly electromagnetic and electrical, can be useful with this aim. In the present paper a case history on the combined use of Electric Resistivity Tomography and Time Domain Electromagnetic soundings is reported. Surveys have been performed within the Maggiore and Traversola Valleys, to investigate the uppermost part of the Quaternary deposits, hosting the near surface aquifer. The electromagnetic data have been inverted with a spatially constrained approach by assuming a quasi 1D model of the subsurface. Geophysical surveys allowed for depicting the depth and lateral continuity of the supposed aquifer level in the surveyed area up to a depth of about 200xa0m and proposing potential positions for well relocation.

Pseudo-3D Characterization of a Geothermal Field through Magneto Telluric

The use of Magneto Telluric (MT) data for geothermal resource assessment is widely documented in scientific literature. Full 3D inversions are however seldom performed since they are time consuming and provide, in most situations, smoothed models which are not suitable for accurate prospection of local anomalies. To overcome these limitations, an algorithm for the pseudo-3D interpretation of MT data based on a spatially constrained inversion is applied. An application to a real dataset is presented to show the potentialities of the selected approach. Data from an extensive MT survey carried out in the geothermal system of Travale (Tuscany, Italy) are presented. Geological constrains from a 3D seismic reflection survey, from geological data and from available stratigraphic logs were used as a-priori information for the inversion and for a correct tuning of the spatial constraints.

Parametric study of cantilever walls subjected to seismic loading

The design of flexible earth retaining structures under seismic loading is a challenging geotechnical problem, the dynamic soil‐structure interaction being of paramount importance for this kind of structures. Pseudo‐static approaches are often adopted but do not allow a realistic assessment of the performance of the structure subjected to the seismic motions. The present paper illustrates a numerical parametric study aimed at estimating the influence of the dynamic soil‐structure interaction in the design. A series of flexible earth retaining walls have been preliminary designed according to the requirements of Eurocode 7 and Eurocode 8—Part 5; their dynamic behaviour has been then evaluated by means of dynamic numerical simulations in terms of bending moments, accelerations and stress state. The results obtained from dynamic analyses have then been compared with those determined using the pseudo‐static approach.

Seismic Characterisation of a Site in the Alps

E002 Seismic Characterisation of a Site in the Alps L.V. Socco* (Politecnico di Torino) D. Boiero (Politecnico di Torino) C. Comina (Politecnico di Torino) S. Foti (Politecnico di Torino) & R. Wisen (Lund University) SUMMARY This study concerns the dynamic characterisation devoted to seismic response analysis of an Alpine test site. We show how integration and combination of different seismic techniques allow a comprehensive characterisation of the site leading to a reliable 2D model for site amplification studies. For the evaluation of the deep structure and the location of the seismic bedrock combined seismic reflection-refraction tests are used while the