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Block-flexure toppling is the most common toppling mode occurring in interbedded anti-inclined slopes. With the development of hydropower projects in Southwest China, numerous deep-seated large-area toppling failures have become revealed along the Yalong River, seriously threatening the construction and operation of hydropower infrastructure. With the Mari landslide as the research focus, a geological field investigation, base friction physical model test, and numerical simulation test were carried out to study the evolutionary process of slope failure. The results demonstrate that the deep-seated toppling in the study area initiated and developed with the river downcutting process, and the landslide was the final result of the toppling deformation. The interbedded structure of layered rock masses, the steep slate foliations in the slope, and the cross joints in the metamorphic quartz sandstone perpendicular to the rock layer are the controlling factors of the toppling deformation. The landslide induced by toppling mainly developed in the highly deformed zone, where multiple failure surfaces developed, and the location and shape of the failure surfaces were controlled by the cross joints in the metamorphic quartz sandstone. The evolutionary process of the deep-seated large-area toppling in the study area mainly underwent four stages: the initial slope formation stage, the rock column bending and cracking stage, the failure surface penetration stage, and the failure stage. [ABSTRACT FROM AUTHOR]

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]

Due to complex geological structures and strong crustal activity, geological disasters occur frequently in the upper reaches of the Yalong River, Southwest China. Toppling failure on anti-dip rock slopes is a common phenomenon; in particular, after the Wenchuan earthquake in 2008, numerous landslides caused by toppling deformation occurred in reservoir areas, seriously threatening the construction and operation of large-scale water conservancy projects and hydropower projects. Taking three typical toppling slopes in the basin as research objects, the dynamic behaviour, failure evolution, and failure plane location of toppling failure under seismic waves were investigated by shaking table tests and UDEC simulations. The test results indicated that slope angle and stratum dip angle were both inversely proportional to the stability of the slope in the tested ranges. The failure evolution of toppling on anti-dip rock slopes could be divided into four stages: (1) the development stage of tensile cracks in the strata; (2) the formative stage of tensile cracks at the crest of the slope; (3) the formative stage of toppling zones; and (4) the failure stage. Two equations were proposed to reveal the relationships between the surface peak ground acceleration and the horizontal depth of the failure plane and displacement of the slope surface. The propagation and coalescence of discontinuous cross joint in the slope and the entire failure evolution simulated by the UDEC damage model agreed well with the shaking table test results. [ABSTRACT FROM AUTHOR]

Block-flexure toppling failure is frequently encountered in interbedded anti-inclined rock (IAR) slopes, and seriously threatens the construction of hydropower infrastructure. In this study, we first investigated the Lean Reservoir area's geological setting and the Linda landslide's characteristics. Then, uniform design and random design were used to design 110 training datasets and 31 testing datasets, respectively. Afterwards, the toppling response was obtained by using the discrete element code. Finally, support vector regression was used to obtain the influence weights of 21 impact factors. The results show that the influence weight of the slope angle and rock formation dip angle on the toppling deformation among tertiary impact factors is 25.96% and 17.28%, respectively, which are much greater than the other 19 impact factors within the research range. For the primary impact factors, the influence weight is sorted from large to small as slope geometry parameters, joints parameters, and rock mechanics parameters. Joints parameters, especially the geometric parameters, cannot be ignored when evaluating the stability of IAR slopes. Through numerical simulation, it was qualitatively determined that failure surfaces of slopes were controlled by cross joints and that the rocks in the slope toe play a role in preventing slope deformation. [ABSTRACT FROM AUTHOR]

A large-scale rockslide, developed from a deep-seated toppling failure, occurred in October 2018 following reservoir impoundment in the upper Lancang River, Southwest China. The evolution of this slope failure was investigated to reveal the instability mechanism of the rockslide after impoundment. Electron spin resonance (ESR) dating was used to determine the formation period of the toppling failure. Detailed field investigations, including joint measurements and surface, borehole and adit surveys, revealed the surface and subsurface features of the deformed rock masses. The Universal Distinct Element Code (UDEC) was used to simulate the evolutionary process of the slope failure. The results show that the toppling deformation rate accelerated with river downcutting and decreased after the modern valley formed. After reservoir impoundment, the mode of slope deformation transformed from creep toppling to rapid sliding. The sliding progressed upslope due to shear failure at the slope toe. In addition, the results of a series of simulations show that the action of tectonic stress can significantly increase the depth of toppling deformation. The investigation results imply that the evolution of the slope failure included five stages: initial deformation, accelerating deformation, creep deformation, formation of a throughgoing sliding surface and failure. The first three stages were dominated by toppling, whereas sliding dominated the latter two stages. Toppling was induced by river downcutting and promoted by the effects of tectonic stress and gravity. Reservoir impoundment promoted sliding at the slope toe, which induced upslope propagation of sliding above the toppling hinge surface. Once the slip zone coalesced with the shear failure surface at the front of the slope, the main rockslide occurred. • Summarize the complexity and distinctiveness of the deep-seated toppling failure • Propose the evolution of the rockslide evolved from deep-seated toppling failure • Reveal the failure mechanism of the rockslide induced by reservoir impoundment [ABSTRACT FROM AUTHOR]

Block-flexure toppling failures in interbedded anti-inclined rock (IAR) slopes present significant risks to infrastructure and safety. Based on the Linda landslide field investigations, this study conducted a series of physical modelling tests encompassing 15 slope angle and bedding angle combinations. The aim of 15 sets of tests was to explore the deformation and failure mechanisms in IAR slopes. The observations during the deformation and failure stages elucidated how changes in slope and bedding angles influence rock mass deformation and failure characteristics. The findings highlight that slope angle critically impacts IAR slope stability, while bedding angle notably affects deformation depth, failure area, and failure surface configuration. IAR slopes with bedding angles less than 60° tend to exhibit shallow, single-surface failures with the linear failure surface, whereas bedding angles exceeding 70° lead to deep-seated, large-area, multi-surface failures characterised by double-folded failure surfaces. The magnitude of the failure inclination angle increases with slope and bedding angles, ranging from 0 to 35°. Furthermore, deformation and failure in IAR slopes involve the progressive extension of cracks from the slope crest to the interior, eventually reaching the slope toe. Finally, the block-flexure toppling process in IAR slopes can be divided into an incubation deformation stage and an accelerated deformation stage, and based on curve characteristics, different deformation modes of the IAR slopes can be further classified as stepwise cumulative accelerated deformation mode and leap deformation mode. Highlights: Fifteen cases of physical modelling tests covering various slope angles and bedding angles were conducted to replicate the deformation and failure mechanism in interbedded anti-inclined rock (IAR) slopes; Slope angle plays a pivotal role in determining the stability of IAR slopes, whereas bedding angle controls slope deformation depth, failure area, and failure surface characteristics; The IAR landslide is a progressive failure process that extends from the slope crest to the slope toe; The deformation process of IAR slopes can be categorised into the incubation deformation stage and the accelerated deformation stage. Additionally, the deformation mode can be further classified as either stepwise cumulative accelerated or leap deformation modes. [ABSTRACT FROM AUTHOR]

Fluctuating reservoir levels and rainfall behind dams generally cause more severe weathering of the rock forming reservoir bank slopes. Physical weathering tends to weaken the rock and can cause slope instability. Slate sampled from a newly built reservoir area was exposed to cyclic wetting and drying to accelerate physical weathering. A series of tests, including uniaxial and triaxial compressive tests, investigated the weakening of slate. Based on the tests, the degradation of the mechanical properties, failure model, and energy evolution process were studied. Cyclic wetting and drying significantly weaken the specimens. Specifically, the mechanical properties show a monotonic reduction with the number of wetting and drying cycles and the confining stress. The average rebound hardness value of the samples decreases from 30.7 to 20.3 as the number of wetting and drying cycles increases from 0 to 10. The weathering degree and mechanical properties of the specimens can be estimated by the rebound hardness through one linear function and six exponential functions. Five types of fractures and three failure modes were found to describe the failure features of the specimens, and cyclic wetting and drying tended to complicate the failure modes. The evolution process of strain energy represented by five specified types can be divided into three stages according to the variations in the energy parameters, and two newly proposed energy parameters can be used to reflect the energy dissipated by micro-fissure closure and fracture generation. [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]

• A damage constitutive model based on Weibull distribution and unified strength theory is developed. • The evolution of damage in rocks is analysed which reflects the damaging extent of rocks. • The physical meanings of model parameters are proved to correspond to reality. The deformation-induced damage of rocks in underground space always results in the long-term instability of engineering projects. In this paper, a damage mechanics based on the constitutive model related to the Weibull distribution and unified strength theory is developed. This model considers the statistical damage, strain softening and damage weakening of rocks in the deformation process. To verify the feasibility of this model, the model parameters were mathematically confirmed, four experimental examples were cited to illustrate the features of the axial pressure versus axial strain under various confining pressures, and five experimental examples were cited to compare the distinction of the axial pressure obtained from the proposed model versus the confining pressure with Mohr-Coulomb criterion. Then, the evolution of damage in the deformation process was analyzed based on the proposed model. Finally, the physical meanings of the model parameters were discussed. The results mainly reveal that the proposed model has a good consistency with the experimental examples, the evolution of damage contains three stages with the deformation process, and the model parameters have distinct physical meanings. [ABSTRACT FROM AUTHOR]

ObjectiveTo determine the association of gestational weight gain (GWG) or pre-pregnancy BMI with postpartum weight retention (PPWR).DesignMeta-analysis.SettingPubMed, Cochrane Controlled Trials Register, EMBASE, Science Citation Index Expanded, Current Contents Connects and Biosis Previews were used to search articles.SubjectsPublications that described the influence of pre-pregnancy BMI or GWG on PPWR.ResultsSeventeen studies that satisfied the eligibility criteria were included in the analyses. Women with inadequate and excessive GWG had significantly lower mean PPWR of −2·14 kg (95 % CI –2·43, –1·85 kg) and higher PPWR of 3·21 kg (95 % CI 2·79, 3·62 kg), respectively, than women with adequate GWG. When postpartum time spans were stratified into 1–3 months, 3–6 months, 6–12 months, 12–36 months and ≥15 years, the association between inadequate GWG and PPWR faded over time and became insignificant (−1·42 kg; 95 % CI −3·08, 0·24 kg) after ≥15 years. However, PPWR in women with excess GWG exhibited a U-shaped trend; that is, a decline during the early postpartum time span (year 1) and then an increase in the following period. Meta-analysis of qualitative studies showed a significant relationship between excessive GWG and higher PPWR risk (OR=2·08; 95 % CI 1·60, 2·70). Moreover, meta-analysis of pre-pregnancy BMI on PPWR indicated that mean PPWR decreased with increasing BMI group.ConclusionsThese findings suggest that GWG, rather than pre-pregnancy BMI, determines the shorter- or longer-term PPWR. [ABSTRACT FROM PUBLISHER]

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]

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]