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The in situ stress field in valley areas is an important factor to consider in the construction of hydropower projects in southwest China. Due to intense tectonic movement, the action of gravity, and rapid river erosion, the resulting stress has a complex distribution and a large magnitude. The availability of stress measurements is insufficient to provide adequate understanding of the regional stress state. In this research, inversion analysis for the in situ stress field of a valley in the upper reaches of the Lancang River is carried out by using stepwise regression analysis and the FLAC3D numerical simulation, and the temporal and spatial distribution characteristics of the in situ stress are obtained. Based on those results, the influence of stress unloading effects on slope stability is discussed. The results show that the formation of the modern in situ stress field is the comprehensive result of interactions among gravity, tectonic movement, and river erosion. The reliability of the inverse result can be increased by improving the mesh density of the calculated model and considering multistep river erosion. Under the influence of the unloading effects, tensile fractures were formed and the rock mass loosened near the slope surface. With the presence of bedding dipping into the slope, toppling failure was triggered by the unloading rebound that mainly occurred in the stress relaxation zone. [ABSTRACT FROM AUTHOR]

Toppling deformations generally develop in interbedded anti-inclined rock slopes in the upper reaches of the Yalong River in southwest China. With the characteristics of large scales, strong deformation degrees and complex deformation modes, toppling bodies may eventually lead to instability failure in the form of landslides, which seriously threaten the construction and operation of hydropower stations in the basin. Taking three typical examples of toppling failures for interbedded anti-inclined rock slopes in the basin, the sensitivity analysis of 19 impact factors affecting the toppling deformation of this type of slope is obtained via the Grey correlation method and UDEC. The results show that the geometric parameters represented by slope angles are the most sensitive to toppling deformation, the mechanical parameters of joints are more sensitive to toppling deformation than the physical and mechanical parameters of intact rocks, and the sensitivities of the parameters of sandstone and slate gradually converge in the deformation process. [ABSTRACT FROM AUTHOR]

Jurassic strata prone to slope failure are widely distributed in the Three Gorges Reservoir region. The limit equilibrium method is generally used to analyze the stability of rock slopes that have a single failure plane. However, the stability of a stratified rock mass cannot be accurately estimated by this method because different bedding planes have variable shear strength parameters. A modified limit equilibrium method is presented with variable water pressure and shear strength used to estimate the stability coefficient of a sloping mass of stratified rock and to identify the potential sliding surface. Furthermore, an S-curve model is used to define the spatial variations of the shear strength parameters c and ϕ of the bedding plane and the tensile strength of the rock mass. This model can also describe the variation of strength parameters with distance from the slope surface, which depends on the reservoir water level. Also, it is used to evaluate the stability of the Qianjiangping landslide, located at Shazhenxi Town, Zigui County, Three Gorges Reservoir area, China. The results show the most probable sliding surface is the interface between a slightly weathered layer and subjacent bedrock. When reservoir water rises above the elevation of the slide mass toe, the stability coefficient of the slope declines sharply. When the reservoir water level is static at 135 m, the stability coefficient decreases gradually as the phreatic line changes as a result of heavy rainfall. [ABSTRACT FROM AUTHOR]

Transversely isotropic rock composed of two interbedded layers has been rarely studied, although landslides frequently occur in bedded rock masses. With reference to the interbedded rock mass in the Miaowei Reservoir area of Yunnan Province, China, this study prepares transversely isotropic specimens made of two interbedded materials to investigate the fracture and mechanical behaviors of interbedded rock. The effect of the bedding plane dip angle and the application of the findings to an anti-dip interbedded rock slope are also studied. Specifically, two groups of isotropic specimens and five groups of transversely isotropic specimens are tested in a series of triaxial compressive tests; based on these tests, the crack types, failure modes and mechanical parameters are analyzed, and one damage model and its application to the failure probability analysis of an anti-dip interbedded rock slope are investigated. The experimental results show that twelve crack types, eight failure modes and five axial stress-strain curve types can be summarized and are significantly affected by the dip angle. The recognition of these crack types and failure modes can improve the qualitative instability analysis of bedded rock masses in the reservoir area, and five mechanical parameters, including peak stress, strain related to peak strength, residual strength, elastic modulus and Poisson's ratio, exhibit fluctuating variation trends versus the dip angle and confining stress due to the influence of the dip angle. Two groups of theoretical curves from the proposed damage model correspond with the pre-peak features of the test stress-strain curves. The proposed failure probability model considering rock damage shows good practicality when applied to an anti-dip interbedded rock slope; the slope displays discrete failure probabilities in various parts, e.g., the slope toe, slope shoulder and weaker layer show higher failure probabilities, and the relaxation behavior increases the failure probabilities and gradually eliminates the discreteness. Relevancy analysis shows that the strength of transversely isotropic rock is more sensitive to the elastic modulus, dip angle of bedding plane, confining stress and composition of the rock. • Transversely isotropic rock made of two interbedded materials is prepared; • Fracture behaviors and damage model of simulated transversely isotropic rock are investigated; • Instability analysis of an anti-dip interbedded rock slope is conducted. [ABSTRACT FROM AUTHOR]

Rock slope monitoring is an important aspect of better understanding the deformation behaviours and failure mechanisms of rock slopes. In this study, a multi-smartphone photogrammetric monitoring (MSM) system for rock slope hazards was proposed and developed. The system, which has nine smartphones embedded in device units, is based on structure from motion and multi-view stereo (SfM-MVS) photogrammetry. All smartphones were controlled remotely only through smartphone applications and the 4G internet. The accuracy of the system under various shooting strategies and light conditions is comprehensively evaluated in terms of both trueness and precision for two rock slopes. The distance errors of target points and the cloud-to-cloud distance were applied to assess the trueness and precision of the reconstructed slope models through the system. The results show that easy-assembly and low-cost systems have centimetre-level accuracy in the evaluation tests. The shooting strategy with a larger overlap rate tends to improve the trueness of the system, and insufficient light conditions increase the distance errors of the system. In addition, a rock slope change detection with 0.006–1.123 m3 was monitored through the MSM system. Owing to these characteristics, the MSM system has the potential to become a helpful method for rock slope reconstruction and monitoring. [ABSTRACT FROM AUTHOR]

Toppling is a widespread failure mode in natural and excavated anaclinal rock slopes and threatens the construction and operation of important infrastructure such as hydropower and transportation corridors in southwest China. Therefore, comprehending the mechanisms underlying toppling is essential for relevant landslide prediction and prevention. In this study, we developed a physical model of an anaclinal rock slope using the Linda landslide as a site case. Based on field monitoring using Gopro cameras, high-speed cameras, strain sensors, stress sensors, and acoustic emission systems, the evolution of the anaclinal rock slope model was analysed. The reliability of the physical model test was verified by comparing the deformation characteristics of the landslide site with those of the slope model. The monitoring results suggested that the slope deformation process could be divided into five stages: an initial interlayer dislocation stage, a deformation initiation stage, a crack generation and propagation stage, a crack penetration stage, and a failure stage. The rock mass could be categorised into four deformation zones: the fresh zone, weakly toppled zone, moderately toppled zone and highly toppled zone. Acoustic emission sensors deployed near the failure-prone region held the potential to serve as early warning indicators for landslides on anaclinal rock slopes. Valley incision played a significant role in the formation of sliding surfaces in anaclinal rock slopes. Furthermore, the model experiment observed multiple failure surfaces and the failure behaviour of the landslide rock mass, shedding light on their connection to the deformation process and the stress state in the model. The study revealed the deformation and failure mechanism of an anaclinal rock slope from many perspectives and deepened our understanding of toppling type of landslides. • Detailed study of Linda landslide's background and structure. • In-depth analysis of anaclinal rock slope using multi-field monitoring. • Summarized complex anaclinal rock slope failure mode and rock mass features. • Emphasized valley incision's role in forming sliding surfaces on anaclinal slopes. • Revealed the generation of multiple failure surfaces during toppling deformation. [ABSTRACT FROM AUTHOR]

Abstract Recent research has paid little attention to the difference in shear strength between discontinuities with different joint wall material (DDJM) and discontinuities with identical joint wall material (DIJM) and what are the controlling factors of shear properties of DDJM. Bedding planes between argillaceous limestone and mudstone in the Badong formation in the Three Gorges area of China were investigated using physical model tests. The effect of joint wall material combination on the shear properties of DDJM was first revealed by conducting tests on a series of artificial joint specimens that were made of different joint wall materials and with varying joint surface topographies under different normal stresses. The results indicate that: the peak shear strength of DDJM is not equal to the lower peak shear strength of DIJM for two joint wall materials of the DDJM, even so it is closer to the lower peak shear strength than to the higher one; effect of joint roughness and normal stress on peak shear strength of DDJM is similar with DIJM; effect of joint wall material combination on peak shear strength of DDJM is greater with larger roughness and higher normal stresses. Based on the data acquired from the physical model tests, a new empirical equation to estimate the peak shear strength of DDJM was developed. The capability of the equation was validated by comparing estimates with data from direct shear tests on natural DDJM samples gained from the Badong formation. Finally, the proposed empirical equation was applied to the stability analysis of a rock slope in the Badong formation. Highlights • Discontinuities with different joint wall material (DDJM) were studied. • Physical model tests were performed to investigate shear properties of DDJM. • Effect of joint material combination was first revealed. • A new equation to estimate shear strength of DDJM was proposed and validated. • The proposed equation was applied in the stability analysis of a rock slope. [ABSTRACT FROM AUTHOR]

Abstract: Lithological information, rock mass fracture data and discontinuity shear strength obtained through field investigations have been used to conduct kinematic and block theory analyses for the rock slopes that exist in the dam site to evaluate the stability of the slopes. The analyses were performed using mean discontinuity set orientations for each rock mass region under gravitational loading to calculate the maximum safe slope angles (MSSA) for different cut slope directions. Results show that final MSSAs obtained from kinematic analysis are less than or equal to that obtained from block theory analysis. The following conclusions have been made based on the block theory analysis results, which are closer to the reality: (1) The final MSSA range between 30° and 47°, 44° and 70°, 47° and 69° for cut slope dip directions of 20–30°, 105–210°, and 270–355°, respectively; (2) For cut slope dip directions of 20–30°, 200–210° and 275–315°, wide ranges of values have been obtained for the final MSSA reflecting the influence of variability of fracture orientations on MSSA; (3) Apart from the region R-d-1 for slope dip directions in the range 20–30°, rest of the regions at the dam site seem to be stable for slope angles less than 40°. Detailed comparisons are given between the kinematic and block theory analyses covering both the theoretical concepts and application results. Also a brief comparison is included between the laboratory and in situ discontinuity shear strength results. [Copyright &y& Elsevier]

Earthquake-induced rock slope failure is one of the most destructive geohazards, posing serious threats to human lives and properties. The potential hazard of a rock slope, under the loading of earthquakes, can be assessed from its failure and runout characteristics, which are however affected by inherent fractures. To simulate the randomness of these inherent fractures, the discrete fracture network (DFN) modeling technique that is based on the Monte Carlo simulation (MCS) is often employed. It is worthwhile noting that different realizations of DFN can be sampled from different MCSs; however, only one realization of DFN is considered and studied in the conventional analysis. There exist differences between the arbitrarily selected DFN and true DFN; as such, the conventional deterministic analysis could cause uncertainty in DFN modeling and the potential hazard of a rock slope cannot be accurately evaluated. In such a circumstance, this paper proposes a probabilistic analysis of earthquake-induced failure and runout behaviors of fractured rock slopes, in which multiple realizations of DFN that are systematically generated with MCS are taken as inputs to the discrete element method (DEM) modeling of slope behaviors, thus, the uncertainty induced by DFN modeling can be explicitly considered and evaluated. [ABSTRACT FROM AUTHOR]

Flexural toppling is one of the main failure modes of natural and manmade anti-dip layered rock slopes. Based on cantilever slab tensile theory, the failure mechanism of flexural toppling was analyzed. A toppling slope is divided into three parts: the stability, tensile and shear zones. By considering this failure mechanism, a new stability analysis method for slopes against flexural toppling failure is proposed using equilibrium theory. In addition, a sensitivity analysis is performed to investigate the locations of possible failure surfaces and zones as well as changes in the stability of anti-dip rock slopes under different conditions. The results show that the positions of the inter-column forces have almost no effect on the stability factor but affect the areas of the tensile zone and the shear zone. The angle of the most dangerous potential failure surface increases with increasing dip angle and slope height, whereas the stability factor is negatively correlated with the dip angle and slope height but is positively correlated with the layer thickness. The failure mode is essentially flexural toppling when the layer thickness is small, but the failure mode gradually transitions to shear-sliding with increasing layer thickness. Finally, a real case study is analyzed using this method, and the calculated results are consistent with the actual conditions. [ABSTRACT FROM AUTHOR]

Complex block-flexure slope toppling is observed in interbedded sandstone and slate in the upper Yellow River, China. Block toppling is observed in the relatively hard sandstone and flexural toppling is observed in the relatively soft slate. The evolution of toppling slope deformation is characterized by long-term progress and spatial variability. In order to study these characteristics, field investigations, adit prospecting, borehole drilling, sonic tests and numerical simulation were carried out. In addition, the effect of the structure, the composite mode of the rock mass, the unloading fissures and geomorphology are discussed. Furthermore, we explored the toppling mechanisms and simulated it numerically; on this basis, the slope evolution is divided into four stages. Results obtained from the numerical simulation compared well with field investigation data (investigation data, rock sonic survey and strata dip statistics). Comparative studies have demonstrated that the analytical methods presented in this paper are appropriate for back analysis of the toppling evolution process. The result showed that this toppling slope has not yet entered the later progressivity failure stage and is currently limited to collapse at shallow levels, whereas the deep-seated rock mass will remain stable for a long time. This study might provide reference for a stability evaluation and hazard prevention analysis for rock toppling. [ABSTRACT FROM AUTHOR]