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The fate of reservoir landslides is mainly dictated by the mechanical behavior of soil in the sliding zone. This soil may be altered under changing environmental conditions of both physical and chemical nature. In this paper, we present a laboratory study on the changing soil properties under complex physicochemical interactions. The soil specimens are subjected to 1, 2, 3, 5, 7, and 10 wetting-drying cycles. The soil strength is determined by triaxial tests. These tests are performed with three types of pore water, namely, acidic groundwater (AGW), normal groundwater (NGW), and distilled water (DW). The deterioration of soil strength, the change in soil microstructure and mineral composition are observed and correlated. Interesting findings for reservoir landslides are drawn: acidic underground water considerably damages the soil microstructure and deteriorates the shear strength compared to normal underground water, while distilled water causes minimal disaggregation. A three-stage micromechanism associated with four physicochemical interactions is revealed, providing insights into microstructure damage and mineral transformation. • Combined effect of physicochemical interaction on the shear strength of sliding zone soil. • Microstructure evolution of sliding zone soil by five classified pores. • Variations in minerals and cations signify potential chemical interactions between soil and water. • Four types of physicochemical interactions in the evolution process of sliding zone soil. • Three-stage evolutionary mechanism for soil deterioration. [ABSTRACT FROM AUTHOR]

The well-known slide-prone red-stratum mudstones in the Three Gorges reservoir (TGR) area are currently undergoing sharp changes in (i) water level driven by the impounding/discharging operation of the Three Gorges dam and (ii) the rain/water H+ concentration driven by recent rapid industrial/agricultural development, and these changes are expected to impact geohazards. This potential impact emphasizes the importance of understanding the role of pH in the drying-wetting disintegration of red-stratum mudstones. Although many investigations have focused on the role of pH in mudstone disintegration, the red-stratum mudstones in the TGR area differ from mudstones elsewhere, and the role of pH has seldom been studied in these rocks. This work adds to the limited body of research by (1) experimentally investigating the possible role of pH in red-stratum mudstone drying-wetting disintegration and (2) revealing the micromechanisms responsible for this role. In the experiment, six disintegration performance indexes and two mechanical indexes, i.e. particle size gradation, slake durability index, decay constant, surface energy, box dimension, fractal dimension, cohesion and friction angle, were monitored throughout the disintegration process. A tri-piecewise linear fractal model is proposed to better describe the particle size distribution. This research shows that the acid enhancements stimulate the disintegration of red-stratum mudstones and significantly affect shear strength. In comparison, alkaline environments inhibit the mudstone fragmentation and slightly degrade the shear strength. Two possible micromechanisms and three potential effects of acid or alkaline agents are presented to account for the role of pH. The findings provide insights into the potential geohazard impacts of sharp changes in the exposure environment (i.e., water level and H+ concentration) of the red-stratum mudstones in the TGR area. • Established a multiphysics database of pH versus disintegration performance indexes. • Revealed the role of pH in drying-wetting disintegration of red-stratum mudstones. • Clarified the micromechanisms of the pH role in red-stratum mudstone disintegration. • Proposed a tri-piecewise linear fractal model of particle size distribution. • Challenged the previous understanding of the pH role/mechanisms in disintegration. [ABSTRACT FROM AUTHOR]

Advances in estimating the three-dimensional (3D) orientation distribution include i) the stereology-based Fouché estimator (FE); and ii) its recent modification (MFE), which has one less meshing step and has three modified components compared with the FE. One way to achieve an accurate estimate is by selecting the optimum estimator. Here, we developed a recognizer for the optimum estimator to help automatically select the most likely accurate estimator for use in the FE and MFE. Before this, we conducted a systematic comparison of the likelihood of obtaining an accurate estimation to clarify for which patterns FE and MFE are likely to perform accurately. The statistical comparison results showed that the MFE was more likely to perform accurately than the FE for patterns of moderately to strongly aligned fracture sets and for patterns of poorly aligned fracture sets with medium to wide intersection angles to the 1D probe, and thus, the MFE was the optimum estimator. For patterns of poorly aligned fracture sets with narrow intersection angles to the 1D probe, however, the FE was more likely to perform accurately than the MFE, and thus, the FE was the optimum estimator. On the basis of these comparison results, we developed a recognizer for the optimum estimator. This developed recognizer provided a simple, reliable tool for selecting the optimum estimator to accurately produce a 3D orientation distribution estimation, which is beneficial to realistic fracture network modelling. Weakness of the developed recognizer was also disclosed. • Clarified in which patterns FE and MFE are likely to produce accurate 3D estimates. • Found that variation in sample size does not affect the optimum estimator selection. • Fracture alignment and probe-fracture angle affect the optimum estimator selection. • Developed a recognizer for the optimum estimator to produce accurate 3D estimates. • The developed recognizer benefits realistic 3D fracture network geometry modelling. [ABSTRACT FROM AUTHOR]

The stability of an arching slope in deformable materials above strong rocks strongly depends on the shape and width of the span. Equations for a free surface problem that incorporate these two parameters were derived using a simplified two-dimensional arching slope model, and were validated using physical model tests under 1g and centrifugal conditions. The results are used to estimate the maximum excavation width for a weak claystone slope in a lignite mine, for which we calculate a safety factor of 1.31. [ABSTRACT FROM AUTHOR]

Red-bed mudstone is widely distributed throughout the Three Gorges Reservoir Area, China. This geological material easily disintegrates into fragments during engineering activities. The potential factors that influence the disintegration (grain composition, slake durability index, grain roundness, fractal dimension, and surface energy) and shear strength (cohesion and friction angle) of red-bed mudstone fragments are investigated via cyclic wetting and drying tests and direct shear tests. The results show that the disintegration process includes three stages and that the grains gradually become well graded. The roundness exhibits a linear relationship with the number of cycles. However, the variations in the slake durability index, fractal dimension (mass-size distribution based), surface energy, cohesion, and friction angle show three distinct stages. In addition, the fractal dimension (quantity-size distribution based) and friction angle are significantly affected by the assumption that the specimens are isotropic, and the grain behaviors involve compaction, rotation, and separation. The cohesion and friction angle display linear relationships with the slake durability index, roundness, fractal dimension (mass-size distribution based), and surface energy, indicating the potential to assess the shear strength of mudstone fragments from the aspect of disintegration. [ABSTRACT FROM AUTHOR]

Fluctuant marine and reservoir water levels are the main failure-inducing factors for embankment slopes. The soft embankment rocks, e.g., red-bed mudstone, eroded by the reservoir water level in the Three Gorges Reservoir area greatly influence the stability of the embankment slopes. In this study, unified strength theory was innovatively applied for damage evaluation and combined with the Weibull distribution to obtain the strength statistics of micro units. Additionally, one damage constitutive model and one damage evolution model considering the initial damage, strain softening and damage weakening were proposed. Then, a series of tests, e.g., modified cyclic wetting and drying test, triaxial compression test and modified numerical simulation test for reservoir embankment red-bed mudstone, were conducted to verify the feasibility of the proposed models. In addition, grey system theory was originally used to evaluate the effects of the Weibull distribution parameters (m and w) and the confining stress on the peak stress. Finally, the proposed model was tentatively applied to the modification of the limit failure height model of the bedded rock slopes. The verification implies that the proposed model results are consistent with the testing results, especially in the simulation of compaction, elastic deformation and strain softening and in the prediction of peak strength. The results from grey system theory analysis indicate that the micro unit strength parameter (w) has the most obvious effect on the strength. Moreover, the modified method based on the damage evolution model for calculating the limit failure height of the bedded rock slopes is conservative. [ABSTRACT FROM AUTHOR]

Cyclic wetting and drying treatment is commonly used to accelerate the weakening process of reservoir rock. The weakening is reflected in strength variation and structure variation, while the latter receives less attention. Based on a series of cyclic wetting and drying tests, this study tentatively applied the uniaxial compressive test, computed tomography (CT) test and digital image correlation (DIC) test to investigate the weakening of slate in a reservoir area. Test results show that the weakening is mainly reflected in the reduction of compressive strength, followed by the decrease of ability to resist cracking and elastic deformation. The weakening seems more likely to be caused by structure variation rather than composition change. Two failure modes, e.g., splitting and splitting-tension, are concluded based on the crack paths: the splitting failure mode occurs in the highly weathered samples and the splitting-tension failure mode appears in the low-weathered samples. The transition zones of deformation are inside samples. The nephogram maps quantify the continuous deformation and correspond to the aforementioned structure variation process. This study offers comprehensive methods to the weakening investigation of slate in reservoir area and may provide qualitative reference in the stability evaluation of related slate rock slope. [ABSTRACT FROM AUTHOR]

• We performed laboratory experiments on anisotropic analogue rocks containing bedding planes and parallel structural flaws. • Co-effects of bedding planes and parallel flaws on rock rupture and fracture coalescence are elucidated. • Experimental results are implied for field occurrences. Mechanical and fracturing behaviors of natural rocks largely depend on the pattern of major discontinuities. The focus of this study is to elucidate the co-effects of the bedding planes and parallel structural flaws on the rock rupture and fracture coalescence. Uniaxial compression tests are conducted on the analogue rock specimens with various combinations of bedding inclinations (from 0° to 90°), bridge angles (-45°, 0° and 45°) and flaw directions (pro-dip and anti-dip). By analyzing the stress-strain curves and the fracture images recorded throughout the test processes, three stress-strain relationship types, six fracture arrays and seven coalescence categories of the structurally anisotropic rocks are generalized. The experimental results show that mechanical parameters, fracture propagation and fracture coalescence are significantly influenced by the arrangement of bedding planes and flaws. The occurrences of the different fracture arrays are also illustrated from the perspective of mechanisms. A careful comparison of the experimentally observed fracture arrays with field examples shows good applicability of the laboratory experiment to the practice. Stress states in the bridge areas are depicted, which account for the macroscopic coalescence patterns. The different coalescence behaviors resulting from the interplay of bedding planes and structural flaws have implications to the faulting process in bedded strata. [ABSTRACT FROM AUTHOR]