查看更多>>摘要：? 2022 The AuthorsWe present the results of new and repeat gallery- and borehole-scale seismic experiments carried out in two excavation damaged zones (EDZs) of 10 (gallery 08) and 20 (gallery 98) years of age at the Mont Terri Underground Rock Laboratory in St. Ursanne, Switzerland. The initial geometry and rock mass properties of the EDZs were studied during and shortly after excavation—allowing for a direct comparison of measurements collected in 2018 to those completed in the past. In gallery 08 parts of the EDZ remain unchanged over ten years, whilst other zones show improvement (i.e., self-sealing) or considerable degradation. In addition, velocity tomograms from 2018 measure extensive areas of p-wave velocity reduction in comparison to the surrounding rock mass at depths shallower than 3.5 m. Isolated extensile fractures are still found in boreholes up to a maximum radial extent of 4.2 m. Data from borehole interval velocity measurements and cross-hole seismic surveys from this gallery suggest the damaged zone still extends up to 1.9 m and 3.1 m radial depth. Refraction seismic results in gallery 98, in contrast, suggest a less pervasive, shallower (<1.0 m) EDZ with a lower frequency of extensile fractures. The smaller circumference of this gallery can in part explain this; however, when compared to various measurements collected during and after excavation, some reduction in EDZ extent is inferable. Both borehole interval velocity measurements and seismic refraction data record p-wave velocity values higher on average than those in gallery 08 and without obvious areas of velocity reduction. Most interval velocity measurements likewise do not measure zones of decreased velocity (e.g., corresponding to rock mass damage) at this location. This suggests more self-sealing has occurred over the twenty-year post-excavation period in gallery 98 in comparison to the ten-year period in gallery 08. As repository safety depends upon the integrity of the rock mass surrounding an excavation, these results are relevant for mid-term assessments of safety (i.e., especially prior to repository closure).
查看更多>>摘要：? 2022 Elsevier B.V.As structural damage caused by expansion of pyrite bearing bedrock and fills had been documented in the UK and other countries since at least the 1960s, it was surprising that some thousands of cases involving extensive damage to residential and other properties near Dublin, Ireland came to light during the first decade of 2000. Although the stability of properties was not immediately endangered, their appearance and functionality were impaired with serious impact on their value, all of which was obviously very distressing to the owners. Various possible causes relating to the ground conditions, construction methods, structural design and materials used in construction were investigated. However, from the characteristics of the damage and the type of fill used beneath concrete floor slabs it was suspected that the presence of pyrite in the fill was resulting in it being subject to damaging expansion. The paper documents investigations carried out in 2008 into the damage caused to houses in one development in north Dublin. Detailed mineralogical and chemical characterisation of the materials concerned confirmed that both cubic and framboidal forms of pyrite were present in the fill material and there was evidence for in-situ expansive mineral formation. Early signs of isolated chemical attack to sub-surface footings and foundation structures was also evident and although no physical degradation of mortar and concrete was apparent, there was potential for deterioration of these buried structures in the longer-term. Various solutions to the problem were suggested, but it was concluded that replacement of the fill with effectively pyrite-free material was the best strategy for remediation. A lack of awareness in the construction industry, particularly the domestic housing sector, of the potential for problems due to pyrite was apparent. This resulted in protracted legal proceedings and new standards and specifications for fill materials were issued. This paper aims to contribute to the understanding of the behaviour of pyrite and its potential for causing problems in construction situations as even with compliance with standards, problems cannot be otherwise ruled out.
查看更多>>摘要：? 2022The potential mechanism responsible for water-weakening effects on the direct tensile failure of rocks remains poorly understood due to the difficulty of experimental control and the occurrence of multiple water-rock interactions. To obtain such knowledge, a series of direct tension tests of marble rock under dry, natural and saturated conditions, coupling with the acoustic emission (AE) signals monitoring, were conducted. Some indices, such as AE energy, the ratio of rise time to amplitude (RA) and the average frequency (AF), were unitized to investigate the micro failure process of marble rock. Test results show that the tensile strength of marble rock significantly decreases with the increase of water content, characterizing variable fracture surfaces. The cumulative AE energy released in each loading stage (i.e., entire loading stage, loading stage before peak stress, and loading stage after peak stress) significantly decreases with growing water content. The greater reduction rate of cumulative AE energy released before peak stress can be result from prominent frictional weakening effect induced by water. Also, investigation of crack classifications and failure patterns based on the polarity and AE parameter methods suggests that, the number of tensile cracks, which dominates the progressive failure process of rock under direct tension, is positively correlated to the water content. The crack classification criterion described as the optimal ratios of AF and RA values in AE parameter method is found to be affected by water content. Finally, the primary mechanism for the marble rock deterioration under direct tension is friction weakening, and the effect of pore water pressure is very limited due to the loading regime. The friction weakening effect is largely attributed to the water film but not likely to the mineral dissolution.
查看更多>>摘要：? 2022The activation of landslides and shallow faults is related to the shear behavior of weak layers during groundwater infiltration. Regarding the water sensitivity of the weak layer in the weathering process, shear softening for weak layers that relies more on damage properties and water content than the requirements of shear displacement and normal stress for quartz grains remains enigmatic. Here, we present the reduction characteristics of the shear resistance and permeability of mudstone granules considering weathering through a dry-wet cycle. Within a shear displacement of 20 mm, the shear mode of the weathered mudstone granules transformed from strain hardening to strain softening when switching from dry to wet conditions. Correspondingly, the permeability perpendicular to the shear zone decreased 10– 45 times with increasing normal stress according to postshear measurements but was not observed for unweathered mudstone and weathered sandstone samples. This was attributed to the insufficient particle crushing of debris in the shear band and low content of fine particles in the macropores. Because weathered particles developed more micropores, the addition of water resulted in clay mineral separation and generated mud that filled the macropores. Thus, the sealing and lubrication effect of the mud rapidly decreased the porosity and shear resistance of the weak layer with increasing particle roundness and uniformity. This transformation mechanism within a limited displacement reveals the effect of water and weathering on the rapid shear softening of weak layers, which helps understand landslide occurrence and shallow fault activation.
查看更多>>摘要：? 2022 The AuthorsRapid urbanization and population growth in Hanoi city raise the demand for groundwater and the risk of land subsidence. This study is the first to conduct a long-term interferometric synthetic aperture radar (InSAR) analysis with different SAR sensors including ALOS, COSMO-SkyMed and Sentinel-1 to evaluate the spatiotemporal evolution of subsidence in Hanoi between 2007 and 2018. The results show that subsidence in Central Hanoi had been diminishing during these 12 years, while the southern and western outskirts (Ha Dong and Hoai Duc district) had become hot spots with peak rates of ~50 mm/yr. We further model the subsidence time-series with 22 years of piezometric records to estimate hydrogeological properties in the area. The modeling yields a mean consolidation coefficient of 0.56 m2/yr, a value typical for aquitards composed of >90% fine-grain materials. The model also predicts another 0.5–1.3 m of subsidence in Ha Dong by the end of this century. Based on these results, we propose zoning for subsidence susceptibility as the basis for future groundwater management in Hanoi. From a regional perspective, Hanoi is relatively less affected by land subsidence compared to other South East Asian cities due to geotechnical factors including small consolidation coefficients, as well as social factors such as lower population density.
查看更多>>摘要：? 2022 Elsevier B.V.Collapse hazards pose a serious threat to the tunnel construction, especially when a tunnel boring machine (TBM) is used. The current methods are mainly focus on the prediction of adverse geology, which cannot provide the specific area that collapse may happen. Recent development of TBM is capable to offer immense amounts of monitored data by the sensors in the machine. A three-stage method was proposed in this study to predict the collapse area in a real-time manner by combining the TBM-generated data with a deep learning algorithm. The method starts with constructing a long short-term memory model to predict torque and thrust based on the data in non-collapse area. This model can then be used to predict the torque and thrust in a real-time manner for the following tunneling. The predicted parameters will be consistent with the measured ones when the tunneling are stable. On the contrary, the prediction accuracy will be decreased when a collapse is prone to happen. A three-stage method is then proposed based on this principle, which is further examined using the big data from Yin-song tunneling Project in China. There were 18 collapses along this 20 km tunnel, 12 of which have been successfully predicted in the second stage and the remaining 6 have been predicted in the third stage. Essentially, the proposed method here is capable to accurately predict tunnel collapse and provide early warning in advance for tunneling, paving the way to a self-driving TBM in harsh geological conditions.
查看更多>>摘要：? 2022 Elsevier B.V.Subsurface imaging by electrical resistivity tomography (ERT) is increasingly used in geotechnical, geo-environmental, and hydrogeological investigation and monitoring. Cross-hole ERT (CHERT) is often used to avoid loss of resolution with increasing depth. However, symmetric artifacts may be induced because the measurement sensitivity around boreholes for some electrode configurations is fairly symmetric. This study aimed to investigate the best practice of ERT for monitoring underground construction or process through an actual scenario of ground improvement with jet grouting columns. The limitation of conventional surface ERT method was first vividly illustrated in an easy-to-understand context. Characteristics and performances of distinct types of CHERT configurations were then studied considering different borehole spacings. Further improvements were explored by evaluating various mixed arrays, model resolution-optimized array, and the comprehensive array. The results show the necessity of mixing two distinct types of electrode configuration. Among various combinations, a combination referred to as the nominal optimal (NOPT) is recommended when imaging resolution, the symmetric effect, and the measurement efficiency are all factored in. Unexpectedly, the resolution-based optimization does not lead to better results and could even induce negative effects. The results also show that the minimum aspect ratio of 2 may not be large enough for imaging complex underground conditions due to reduced sensitivity and increased 3D effect. The above findings are justified by the eigenvalue spectrum of the Hessian matrix, which is considered a better appraisal index than the model resolution for CHERT.
查看更多>>摘要：? 2022 Elsevier B.V.Uncertainty in geological models, mainly caused by natural heterogeneity and inadequate data, often leads to substantial societal risk including failures of engineered structures, geohazards, and groundwater and environmental problems. These models mainly depend on geological knowledge about evaluation of rock mass quality, fractures/faults and clay. Traditionally, geotechnical parameters of rock mass quality classification, such as rock mass integrity index (Kv) are obtained by drilling tests. However, the boreholes approaches are time-consuming and expensive, provide limited data and have topographic constraints. Alternatively, the inexpensive integrated approaches of geophysical methods can reduce geological ambiguity by bridging the gaps between accurate subsurface models and inadequate borehole data. In this work, we incorporate electrical resistivity tomography (ERT) with inadequate drilling data, and determine Kv over large area even where no borehole exists. Our results reduce a large number of wells and evaluate the subsurface thoroughly using 2D/3D imaging of Kv. The ambiguity in water-clay differentiation caused by low resistivity was resolved by integrating ERT with induced polarization (IP). The integration of ERT, Kv and IP identified several localized fractures/faults. Our novel approach, compared with the past studies, reduces uncertainty in the geological model and provides a thorough insight into the subsurface for infrastructure design and groundwater assessments. Our approach is applicable in most cases.
查看更多>>摘要：? 2022 Elsevier B.V.Although a fundamental part of landslide dam risk management, the evaluation of the spatial probability of dam formation is a challenging problem. In this study, we developed a new method for evaluating the river damming susceptibility of active landslides and unstable slopes (ALUSs), which combines a logistic regression model with time series Interferometry Synthetic Aperture Radar (InSAR) techniques. The approach is applied in the Bailong River Basin, on the eastern edge of the Qinghai-Tibet Plateau, China. We established a primary assessment model using historical damming and non-damming landslide data based on a logistic regression model. Jack-knife analysis showed that the most significant factors controlling river damming susceptibility were valley width, landslide volume, internal relief, and river discharge, in order of decreasing significance. Seventy ALUSs were detected by the InSAR technique and their volumes were predicted using a Volume–Area empirical power-law relationship. The river damming susceptibility of these instabilities was assessed and the results show that 18 of them have a high or very high probability of river damming. Four active landslides with volumes >107 m3 were found to be prone to forming complete blockage conditions, as identified by the Morphological Obstruction Index (MOI). The predictive ability of the methodology was tested using two recent river damming cases and the prediction results were in good agreement with reality. Our approach can potentially help in the early identification and hazard assessment of landslide damming in the Bailong River Basin and similar alpine areas.
查看更多>>摘要：? 2022 Elsevier B.V.In geotechnical engineering, the need for efficient and economical site characterization is the main motivation for the development of new techniques. This study combines electrical resistivity tomography (ERT) with piezocone penetration test (CPTU) to develop a rapid site characterization tool. The feasibility and efficiency of delineating subsurface structures, mapping the lithology, and estimating the hydraulic conductivity of subsoils are verified at a construction site. The lithologic information obtained via this rapid tool is validated using borehole data. According to CPTU results, the subsurface discontinuity exhibited in the ERT section is related to variation in the water content of silty sands. Accordingly, rapid and economical subsurface characterization can be achieved by using ERT survey to optimize the number and locations of point-based geotechnical tests, especially CPTU. We outline the applicability of using CPTU and ERT-derived resistivity data to predict the hydraulic conductivity of cohesive and sandy soils, respectively. A non-simplified Archie's law is used to relate the resistivity of sandy soils to their hydraulic conductivity, and appropriate values of this law's model parameters are proposed.
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