查看更多>>摘要：The Castelnuovo village is placed on a small NW-SE trending ridge, approximately 60 m higher than the valley floor, occupying a portion of the larger continental L'Aquila Basin (Central Italy). During the April 6, 2009 L'Aquila earthquake (Mw 6.3), the village suffered heavy damage. Several studies investigated the local seismic amplification of the Castelnuovo area employing geotechnical, geophysical, and geological surveys, together with 1D, 2D and 3D numerical models. However, all these studies relied on shallow geotechnical and geophysical surveys, which do not reach the engineering bedrock and do not constrain the presence of an impedance contrast at depth. To date, no detailed study has been carried out to assess the depth of the engineering bedrock. In this work, we fill this gap by executing two deep boreholes reaching the engineering bedrock, tied with an extensive campaign of microtremor measurements all over the Castelnuovo ridge and the surrounding plain. The interpretation of such new data, together with analytical, numerical, and geostatistical techniques, demonstrates that local seismic amplification is linked to a strong impedance contrast at more than 200-m depth beneath the Castelnuovo village associated with the lithological transition between clayey silts and breccias. Such results differ from those provided by previous studies, where such impedance contrast was considered shallower, and represent a milestone for assessing the local seismic hazard of the area.
查看更多>>摘要：Slope failure near a reservoir area is mainly influenced by rainfall and reservoir water fluctuation. This study provides insights into the deformation and failure process of the Bianjiazhai landslide near the Suofengying reservoir located at the Wu River in Guizhou province, China. Firstly, stability analyses were carried out to assess the overall strength of the slope and identify the most vulnerable section of the site. Secondly, transient hydromechanical analyses were performed to analyze the effects of rainfall and the reservoir water level fluctuations on the selected slope. The hydromechanical analysis is divided into three different scenarios to study combined as well as the individual effects of rainfall and reservoir water level fluctuation on slide formation. The results indicate that the sudden reservoir water level fluctuations are critical for the stability of the slope. Strength reduction analyses confirm that the deformation behavior of the slope is dominated by shear slip phenomena and identify relevant shear zones. The numerical results from both hydromechanical and stability analysis indicate that the stability of the slope is greatly reduced during large and sudden drawdown. The results from this study will be useful for preventing landslide disasters and for guiding reservoir operation in a similar context.
查看更多>>摘要：Recent studies have assessed that slope-vegetation-atmosphere, SLVA, interaction may trigger the activity of deep landslides in clayey slopes. In some cases, the presence of an underground aquifer, fed by an upstream hydraulic recharging area, may represent a predisposing factor of such activity, being co-responsible of deep piezometric heads, which can undergo seasonal fluctuations due to the SLVA interaction. In this perspective, the present paper illustrates the results of a scientific research, carried out in a pilot site of the Daunia Apennines, the Fontana Monte slope at Volturino (Foggia, Italy), considered as a prototype of the class of landslide mechanisms controlled by both the rainfall water infiltration and the presence of a water-bearing aquifer in the hillslope. Numerical simulations of the saturated/partially saturated transient seepage flow in the slope have been performed by means of uncoupled hydraulic finite element analyses, with the aim of investigating the sources of large piezometric heads, related to climatic, hydrogeological and hydraulic slope features. The rainfall and evapotranspiration fluxes, the latter defined through the FAO Penman-Monteith method, are both implemented as ground surface input, while seasonal variations of the upstream hydraulic boundary conditions are imposed to predict the seasonal piezometric excursion at shallow and deep monitoring points. The transient seepage results are then used as input for limit equilibrium analyses to assess the influence of the hydraulic settings on the stability of the considered landslide body. The work shows the impact of both climatic and hydraulic factors on the seepage processes, affecting the stability of the slope. Moreover, it is highlighted that the accurate implementation of the upstream hydraulic feeding is fundamental for a reliable prediction of the monitored piezometric regime, strictly related to the recharge of the water-bearing aquifer.
查看更多>>摘要：Mitigation measures aimed at reducing the landslide hazard often consists of drainage systems, in particular when the piezometric regime in the slope is identified as an internal factor predisposing the landslide to fail, the latter is very often the case when weather-induced landslides are dealt with. In the past such mitigation measure has been considered eligible solely for shallow landslide mechanisms. However, some authors have reported that the variation in piezometric regime at large depth becomes no more negligible if a medium depth drainage trench system is installed. Nonetheless, the efficacy of a drainage trench system is often hard to quantify because of the high-level computation process that needs to be undertaken, since it has to include, in principle, several parameters describing the saturated-partially saturated hydro-mechanical behaviour of the material as well as all the processes occurring when interacting with the vegetation and the weather; this is even more complicated due to the geological history and the resulting geo-hydro-mechanical (GHM) context to deal with. As such, the determination of the efficiency of a drainage system represents still an open issue in the engineering practice, since this issue relates to a transient hydro-mechanical (HM) boundary value problem. Very often the design of such mitigation measures has been pursued by using design-charts determined under simplified hypotheses. In this paper, the effects of implementing the geological history of the slope of reference, representative of a widely spread landslide mechanism type across the GHM context dealing with, have been investigated on the drains-induced transient seepage, being computed by means of advanced fully coupled two-dimensional HM numerical modelling. The HM numerical analyses reported in this contribution address to a reference case study in the Eastern sector of the Southern Apennines region, which has been selected as prototype landslide in the assessment of the stabilization efficacy of deep drainage trench systems.
查看更多>>摘要：The rupestrian habitat is a distinctive element of the Mediterranean landscape. It is made of structures excavated in the rocks and making benefit from the availability of weak rocks or the presence (in earlier period) of natural hollows and rock shelters. Typical examples are from all over the Mediterranean region, such as the sepulchral monuments and temples which date back to the years before the Christian era (Hittitian, Egyptian, Etruscan, Hellenistic Nabatean and early Christian structures) or the underground town and churches in Christian, Byzantine and medieval period (Caucasus, Anatolia, Ethiopia). Responsible institutions, as well as UNESCO, are deeply involved in programs for mitigating the risk and proposing a proper maintenance plan. In the present paper some case studies have been investigated, to show anthropological and structural similarities among them, but also geological, geomechanical and geomorphological ones. Etruscan monuments and temple of Tarquinia and Norchia (Italy), Petra and Al-Ula (Nabatean kingdom), Byzantine rupestrian Heritage in the Caucasus (Georgia) and some others, may offer a clue to understand the interconnection of Mediterranean cultures during the time. On the other hand, considering their geological and topographical properties, the main acting processes are slope instability on a rock material, that sometime shows a behavior that is at border between weak rock and stiff soil and where water and weathering may play a relevant role in their morphological evolution and future survival. In such conditions the main effort is to preserve them from an irreversible damage and to maintain their integrity and authenticity, making use of a strategy based on deep knowledge, advanced monitoring, low impact mitigation approach, integrated with the enhancement of local capacity and expertise.
查看更多>>摘要：The behaviour of soils and rocks containing clay minerals is the effect of complex chemo-mechanical processes of interparticle interaction. This paper presents experimental results and model simulations of the influence of mineral composition and pore fluid composition on swelling and swelling pressure of clayey soils frequently affected by instability problems. The soil from a landslide in tectonized clay shales, characterized by wide ranges of plasticity and activity, was analysed. Soil fractions at different liquid limit wL were reconstituted with distilled water or salt solutions at different concentrations and they were compressed in oedometric conditions. The tendency to swell was induced by unloading or by exposure to a fluid different from the pore fluid. Swelling was permitted in a set of specimens and it was prevented in another set by applying increasing pressures. The temporal evolution of swelling and swelling pressure was monitored, and ion concentration in the pore fluid was evaluated by monitoring the cell fluid composition. The chemically induced swelling was very large in the most plastic soil and negligible in the least plastic. Swelling pressure too attained different values, however, it was also very large in the least plastic soil. The observed coupled chemo-mechanical processes were successfully modelled with the FEM method by using a user-defined UEL subroutine that was implemented in the commercial code ABAQUS. The subroutine takes account of the chemo-mechanical interactions in the solid skeleton, through a suitable constitutive model, and of the coupled fluxes in the porous space, in addition to water desorption/adsorption at clay platelets. In the proposed constitutive model, chemical interactions are assumed to affect both the plastic and the elastic response, as it was observed in experiments, thus an extended elasticity law is proposed. A simplified analysis, calibrated on the model results, shows that the role of swelling/swelling pressure on slope stability is significant even in the case of the least active soil. A decrease in pore solution concentration thus provokes two effects that are both negative for slope stability: a decrease of strength parameters and an increase of horizontal stresses.
查看更多>>摘要：In a recently completed research study, two-dimensional (2D) and three-dimensional (3D) seismic response analyses were performed on a hydraulic fill earthen dam located in north Texas, USA. Analysis results obtained from both methods were compared to study and address the influence of geomaterial variability on the seismic response of heterogeneous earthen dams such as hydraulic fill dams. For evaluating the material variability within the dam, twenty-eight piezocone penetration soundings (CPTu) were conducted along the crest of the dam. These CPTu soundings, along with the available laboratory test results, were utilized to represent various scenarios that depict geomaterial variability within the dam for numerical modeling and seismic response analysis. In the first scenario, limited subsurface investigation information obtained from six CPTu soundings distributed along the dam crest was considered to develop the numerical models. In the second scenario, all the twenty-eight CPTu soundings were utilized to model the same dam using extensive site characterization test results. The first natural frequency, earthquake-induced crest accelerations, and shear stresses of the dam segments were computed from 2D and 3D numerical analyses for both scenarios of site characterization results. Results indicated that a 3D analysis might be more appropriate than a 2D analysis for studying the seismic response of a heterogeneous earthen dam, especially when extensive site characterization information is available to model the dam for numerical analyses. Overall, the findings of this study emphasize the impact of geomaterial variability on seismic response analyses of heterogeneous earthen dams and will enable engineers to assess the conditions that warrant a comprehensive 3D analysis.
查看更多>>摘要：? 2018 Elsevier B.V.The authors regret that there is a typographical error in Eq. (6). The equation should read: [Formula presented] The authors would like to apologise for any inconvenience caused.
查看更多>>摘要：Deciphering deformation mechanisms within Quaternary sediments in a highly dynamic environment such as the southeast European Alps is often a challenging task that requires the use of a variety of methods. Due to the geohazards involved, the interpretation of deformation mechanisms can have a major impact on society and may enable the preparation of appropriate engineering solutions. We present an example of how deformation structures can be studied by integrating geomorphological, sedimentological and structural geological mapping using photogrammetric and leveling surveys, paleoseismological techniques, optically stimulated luminescence dating and ground penetrating radar surveys. Quaternary deposits on the slopes of the formerly glaciated So?a Valley near Most na So?i are tilted and dissected along numerous faults within the deformation zone of the Idrija Fault, a large, active, dextral strike-slip fault. Reconstruction of deformation history indicates that at least five deformation events occurred during deposition of the glaciofluvial succession interbedded with glaciolacustrine deposits, dated to Penultimate Glaciation. Ground penetrating radar profiles and outcrop observations reveal NE – SW striking faults, which are approximately perpendicular to the primary Idrija Fault. Based on the local geologic setting, we considered glaciotectonics, gravitational faulting due to ice-decay collapse or slope instability, and tectonic faulting as possible deformation mechanisms. Based on detailed documentation and analysis of the geometry and kinematics of the deformations, we interpret the observed deformations as secondary structures that result from paleoseismic activity of the Idrija Fault, and some structures resulting from glaciotectonics and gravitational faulting. The transtensional type of deformations at the studied site shows the local character of the main fault, which occurs here due to geometrical and kinematical changes of the Idrija Fault causing local transtension in the Most na So?i area. The complexity of the fault and the first paleoseismic evidence dating back to Penultimate Glaciation provide valuable new data for understanding the seismic hazard in the region.
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