查看更多>>摘要：? 2022The weakening effect of water in rocks has been extensively investigated over the past few decades. The degradation of the strength and stiffness of rocks can vary greatly with rock type. To investigate the water-weakening effect on the mechanical properties and failure modes of a Hydropower station's bedrock, static and cyclic triaxial compressive tests were carried out on dry, natural, and saturated tuffs (from the Badantoru Hydropower Station in Indonesia) under different confining pressures. Analysis of the failure modes, stress-strain curves, and brittleness index revealed that all of the samples exhibited typical brittle fracture behavior, i.e., a stress drop, volumetric dilation, and no compaction bands. The decreases in the peak stress, residual stress, and elastic modulus with increasing water content verify the water-weakening effect. The correlations between the water content and the confining pressure and other characteristic parameters calculated using the Pearson correlation coefficient indicate that the peak stress and elastic modulus are negatively correlated with the water content, and the peak stress, peak strain, and elastic modulus are positively correlated with the confining pressure. Compared with the Mohr-Coulomb criterion, the Hoek-Brown criterion can better describe the failure behavior of tuffs. Two damage variables, DE and Dε, were defined based on the hysteretic energy and residual strain. Both can characterize the damage evolution and failure mechanism, and DE can describe the stages of the damage evolution in more detail.
查看更多>>摘要：? 2022 Elsevier B.V.The instantaneous profile (IP) method is widely used for determining the coefficient of permeability of unsaturated soils. IP method requires the measurement or control (i.e., zero flux) of flux at any one end of a soil profile. Besides, there are requirements of variations in volumetric water contents (VWCs) and pore-water pressures (PWPs) at various points from the above-mentioned one end of the soil profile to a particular point in which the unsaturated coefficient of permeability is derived. The measurement or control of flux at one end of the soil profile requires high accuracy which causes difficulty while performing tests in the laboratory and field. To overcome the difficulty of the IP method, this study proposes a new simplified transient method for determining the coefficient of permeability of the unsaturated soil. Variations in volumetric water contents and corresponding pore-water pressures at three points are required in the new simplified transient method. The intellectual advantage of this method as compared to the IP method is that there is no need to measure or control the flux at one end of the soil profile. Therefore, this new method is more practical and is expected to be widely used in both laboratory tests and field tests. The validity of the new simplified transient method is verified through numerical simulations considering a one-dimensional seepage for four different types of soils including coarse-grained soil, sand, clay, and silty sand with gravel. The applicability of the new simplified transient method is demonstrated by comparing the unsaturated coefficients of permeability of soils computed by the new simplified transient method and the IP method. Good agreements in comparisons prove that the new simplified transient method is effective for determining the unsaturated coefficient of permeability of soil regardless of soil types and hydraulic functions features.
查看更多>>摘要：? 2022 Elsevier B.V.Geotechnical and geophysical testing data are conventionally considered as separated information or combined based on deterministic methods in site investigation programs, which causes loss of information and introduces additional uncertainties. This study aims to reduce the uncertainties and costs in inhomogeneous soil profile characterization and geotechnical analysis by quantitatively integrating these data. The intrinsic collocated co-kriging method (ICCK) is utilized to integrate Multi-channel analysis surface wave (MASW) and CPT data. This research shows the potential of using the MASW data to explore the horizontal scale of fluctuation (SOF) of the cone tip resistance (qc) field which is very difficult to get using the conventional methods due to the limited CPTs. The Markov model is used to avoid the tedious modeling of the cross-covariance relationship in the ICCK method. A series of synthetic case studies show that the combined soil profile is in good agreement with the “true” qc field with significantly reduced uncertainties. Based on estimating the uncertainties, the optimal distance between CPTs is suggested to be 1–2 horizontal SOF. This framework is also applied to a real case in the Christchurch area, which involves integration of CPTs and MASW tests. Cross validation and edge detection methods are used to quantitatively compare the integration results, confirming that the proposed framework is fully applicable to field data and can provide realistic and reliable estimations of qc field.
查看更多>>摘要：? 2022This paper focuses on Biot's coefficient measurement of saturated COx claystone. The tests were systematically conducted to provide clarification on its value as the available literature indicates quite erratic results from 0.26 to 1. The difficulty of this work mainly lies in the time that is necessary to stabilize each loading step (confining pressure and/or pore pressure) and also in sample preparation. Two main results were obtained: 1) Whatever the initial conditions were (confining pressure Pc amplitude, hydric state, damaged or not…), all samples exhibited a significant anisotropic swelling during the first water injection; 2) even being a transversely isotropic rock, its Biot's tensor is (quasi) isotropic thus leading to a unique coefficient “b” which is very close to 1. Such results are consistent with what was observed with gas as being the fluid to control pore pressure in partially saturated samples.
查看更多>>摘要：? 2022 Elsevier B.V.The shear characteristics of soil on the basal face of a landslide body have important implications on landslide dynamics. In this study, ring-shear tests were carried out on quartz sand to study the shear characteristics of soil particle materials on the basal facies. Quartz sand samples of different particle sizes (0.25–1 mm) were treated at high temperature (20–800 °C) to determine the influence of temperature and particle size distribution (PSD) on their shear characteristics at different shear speeds. The shear characteristics of the samples were analyzed, including the shear stress, shear stress fluctuation, density variation, and degree of fragmentation. The results show that the amplitude of shear stress fluctuation increases with increasing shear velocity. It can be determined that the smaller the particle size, the greater the residual shear strength. Elevated temperature has a certain influence on the quartz sand and the shear characteristics (e.g., shear stress) exhibit a low degree of deterioration. The dilatancy and compaction mechanism of the samples under large displacement shearing is further discussed.
查看更多>>摘要：? 2022 The AuthorsThe active deep-seated Marzellkamm rock slide is situated in the high mountainous region of Tyrol (Austria), which has been subjected to the most recent deglaciation since the Little Ice Age (LIA). This study presents the investigation of initial rock slide formation and deformation mechanisms with respect to the structural geological inventory and the recent glacier retreat of approximately 2.2 km in length and 160 m in thickness since 1893. An integrated approach comprising field-based rock mass characterisation, glacier reconstruction based on historical maps (1893–1949) and remote sensing data (1953–2017), multi-temporal morphological analysis (1971–2019), and 2D distinct element modelling was applied. We show that deformation features mapped on the surface are reproduced by numerical modelling, and that (i) rock slide formation and slab development originates along pre-existing fault zones, (ii) a sliding mechanism occurs along a predefined fully persistent, curved but non-circular basal shear zone, and (iii) meso-scale fractures (e.g. joints) have only a minor impact on rock slide formation. Glacier reconstruction and deformation analysis show that increased slope displacements are directly associated with accelerated deglaciation rates between 1893 and 2017. Stable slope conditions were obtained by modelling as long as half to one third of the lower slope was covered by glacier ice, i.e. before the 1969 glacier stage. Rock slide movement is assumed to have initiated during the basal shear zone formation from 1949 onwards. Triggered by the general sliding movement, shear displacement along pre-existing fault zones led to the formation of rock slide structures and the separation in individual slabs and blocks. Our study shows that detailed geological mapping and deformation monitoring in combination with numerical modelling techniques can create a promising rock slide model.
查看更多>>摘要：? 2022Soft soils are widely distributed in the Guangdong-Hong Kong-Macao Greater Bay Area of China. The soft soils are featured with large water content, high compressibility and low permeability, posing great challenges in dealing with bearing capacity and foundation settlements. Extensive laboratory tests have to be conducted to determine parameters for shear strength and compressibility properties of soft soils. This is really time consuming and costly. In addition, sample disturbance and lab testing error are also unavoidable. The aim of this study is to develop a simple, efficient while satisfactorily accurate tool for prompt assessments of parameters for shear strength and compressibility of soft soils. The artificial neural network (ANN) technique is employed to reach this goal. A large database is first presented for measured physical and mechanical parameters of soft soils sampled from a core city in the Greater Bay Area. The data are obtained from six types of geotechnical laboratory tests, including direct shear test, consolidation test, unconsolidated undrained test, total stress consolidated undrained test, effective stress consolidated undrained test and compression test. Then, the ANN is applied to map the shear strength and compressibility properties of the soft soil from its physical parameters. The analytical forms of the ANN models are derived and presented to enhance their practical value. Next, the accuracies of the six ANN models are evaluated using model bias statistics where model bias is the ratio of measured to predicted value. The evaluation results showed that the ANN models are practically unbiased on average and the dispersions in prediction accuracy are low. Furthermore, the probability distributions of the model biases are characterized. This study helps saving time and cost of geotechnical investigation for soft soils in the area.
查看更多>>摘要：? 2022 Elsevier B.V.Slope stability is mainly assessed by the factor of safety (FS) parameter. As an improvement to the integral FS derived from the conventional limit equilibrium method (LEM), the local factor of safety (local FS) is used to describe the FS of each material element. However, although current slope stability algorithms with LEM rely on only strength criteria, some areas of a slope show almost no displacement, even though plastic yielding is occurring within the slope. For these reasons, we developed a new approach for defining the local FS based on the displacement isosurface. Adopting the Mohr–Coulomb (M–C) strength criterion, this new algorithm calculates the local FS in the potential sliding zone with a change in the apparent displacement. Based on the shear strength reduction technique, the distributions of the local FS within 2D homogeneous slopes with different shear strengths and within a real 3D slope with a complex topography are analyzed. Firstly, the applicability of the new approach was examined and we found that the local FS decreases significantly only when the direction of the yielding surface approaches the displacement direction, which also reveals that the LEM may underestimate the FS. In addition, the areas of a slope where the local FS strongly changes depend on the slope geometry and also control the instability patterns. Further, the results of a local FS in a 3D slope analysis show that complex topography and internal structure can cause the alternation of stable and unstable blocks in the slope and that the mobilities of the blocks induced by the instability differ in different areas. Finally, some local optimized retaining countermeasures were successfully implemented for supporting a real engineering slope guided by the local FS. Our results indicate that this improved algorithm can provide a more suitable and accurate local FS with which to assess slope stability and reveal more realistic instability patterns than approaches using the integral FS.
查看更多>>摘要：? 2022 Elsevier B.V.High temperatures lead to thermal fracture in the rock, which can greatly impair the rock's mechanical properties. During Jiweishan landslide, rocks on the sliding surface generate high temperatures due to frictional heating. Studies on thermal fracture during landslides and its influence on the sliding process are unclear. Here we use thermogravimetry and dilatometry to study the thermal expansion and thermal fracture of the rocks at the base of the 2009 Jiweishan landslide. Experimental results show that rocks generate a large number of thermal fractures and thermal expansion while reaching temperatures of up to 827.3 °C. The generation of CO2 gas also significantly produces and promotes thermal fractures. This indicates that the rapid heating process during the Jiweishan landslide could have caused thermal fractures on the sliding surface during the landslide, which could have then weakened the mechanical properties of the rock, making the sliding surface more susceptible to entrainment. As a result, the sliding surface lost frictional resistance during the landslide, resulting in a faster sliding velocity and a longer sliding distance. In addition, we infer that thermal fracture is beneficial for CO2 gas to be released from the rock and enter the sliding zone, which may produce pore pressure, reduce the effective normal stress on the sliding surface, and which also contributes to the lubrication.
查看更多>>摘要：? 2022 Elsevier B.V.Affected by groundwater fluctuations, the loess around the hydro-fluctuation zone near the groundwater table is frequently subjected to periodic dry-wet cycles. The investigation on the creep characteristics and microstructural evolution associated with the mechanical response of loess after the application of dry-wet cyclings is of great significance to better understand the loess landslide mechanism. Triaxial creep tests and scanning electron microscopy (SEM) were conducted on intact loess specimens obtained from Heifangtai platform, Gansu, China. The micrographs were processed using IPP software and the microstructural information of soil pores were obtained. Results of triaxial creep test revealed that the application of dry-wet cyclings causes the creep deformation of loess soils to increase significantly, and they showed that the long-term strength and dry-wet cycle follow an exponentially decreasing function, indicating that the reduction in the long-term strength of loess soils is greater in the first five dry-wet cycling compared with that in the subsequently dry-wet cyclings. The microstructural analysis showed that aggregates were found to cluster upon the application of drying-wetting cycling, followed by the rearrangement of soil skeletons, transforming the initial relatively dense structure into a loosen one with a greater percentage of macro-pores which are more sensitive to creep deformation of loess soils. Additionally, it is observed that the microstructural evolution is dependent on the number of dry-wet cyclings. As the dry-wet cycles increase, the flatter and irregular macro-pores increased gradually at the expense of meso-pores. In addition, the mechanism of irrigation-induced loess landslides is revealed from the perspective of variation in creep characteristics of loess after the dry-wet cycles, which can be summarized into three stages, namely, the dry-wet cycle stage of the loess around the hydro-fluctuation zone; the long-term creep-liquefaction stage of the deep loess, and the slip surface transfixion stage.
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