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Rainfall with heavy intensity and long duration is a main inducing factor that triggers landslides on anti-inclined rock slopes. Numerous interbedded anti-inclined rock (IAR) slopes in Southwest China frequently experience mountain collapses and landslides under heavy rainfall. Therefore, it is necessary to study the failure mode of IAR slopes during rainfall. In this study, the Linda landslide and Mari landslide, typical IAR landslides in the study area, were used as examples to build a physical model of IAR slopes under continuous rainfall conditions, and a self-made rainfall simulation system was used to mimic natural rainfall conditions. The multi-physics data of displacement, velocity, stress, strain, pore water pressure, and acoustic signals in model deformation and failure under rainfall conditions were obtained using multi-field monitoring technology. In addition, the materials' water content and mechanical parameters at different locations of the model were obtained after the experiment. The analysis results indicate that: in the first and middle periods of rainfall, the slope model experienced a shallow local deformation and a holistic toppling deformation; until the late rain, the failure of the IAR slope caused by rainfall finally presented a typical failure mode of multiple failures and collapses of regressive landslides. According to its multi-field evolution characteristics, the velocity and acoustic signals were highly consistent with the failure characteristics of the model, which could be used as landslide early warning indicators. In addition, it was observed that the shape of the multi-slip surfaces generated by the model was a concave double straight line extending from the slope toe to the slope surface and sharing the failure section at the slope toe. Finally, the deformation and failure process of the model could be speculated to be divided into five stages based on the deformation behavior and multi-field physical data feature: the initial interlayer dislocation stage, the deformation stage, the crack propagation stage, the retrogressive failure stage, and the holistic failure stage. The failure mode and deformation mechanism of IAR slopes under rainfall were revealed in the model test, which could provide appropriate guidance for the analysis and evaluation of similar landslides. Highlights: The failure of the interbedded anti-inclined rock slope model caused by rainfall presented a typical failure mode of multiple failures and collapses of regressive landslides. The velocity and acoustic signals are highly consistent with the failure characteristics of the model, and the shape of the multi-slip surfaces was a concave double straight line extending from the slope toe to the slope surface. According to its multi-field evolution characteristics, the deformation and failure process of the model under rainfall conditions can be divided into five stages. [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]

This paper outlines the spatial-temporal evolution of a landslide. A multiple monitoring system that consists of a three-dimensional (3D) laser scanner, a particle image velocimeter (PIV), earth pressure cells (PCs), and a thermal infrared (TIR) imager were designed and employed for a 1 g landslide model case study. The displacement, velocity, lateral earth pressure and surface temperature were recorded during the evolution of a landslide. Four stages of evolution were identified using the measured displacements: the initial stage, the uniform stage, the accelerated stage and the failure stage. The deformation, lateral earth pressure and surface temperature of a landslide were monitored during each stage. The distribution of the lateral force with depth varied significantly during movement, and the depth of the maximum soil pressure increased with movement. The surface temperature of the moving mass was significantly higher than the surface temperature of the nonmoving mass. The average change in surface temperature showed a significant increase in surface temperature followed by a decrease in surface temperature prior to failure. This study provides procedures and solutions for landslide monitoring, interpreting landslide initiation and detecting landslides. [ABSTRACT FROM AUTHOR]

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]

Huangtupo landslide, volumetrically the largest, most complex landslide in the Three Gorges Reservoir region of China, is a dangerous mass on which the district of Badong has been inadvertently situated. Risk remediation efforts include the construction of a large observational tunnel and monitoring system that are unique in the world. This tunnel and its side branches permit detailed mapping of its 3D structure while providing samples for laboratory analysis. The new investigations validate that the Huangtupo landslide is a composite of several independent landslides and that movement occurs along the major rupture zones as well as on interlayer sliding zones in the underlying Badong Formation. Uranium-thorium disequilibrium dating establishes that the northern part of the landslide, called the Riverside Slump, underwent at least two periods of movement at about 100 and 40 ka (ka stands for a thousand years). These events were induced by the steep slope created by the downcutting of the Yangzte River. The results from in situ displacement monitoring over a 7-year period confirm that the central part of the landslide is creeping at a slow, relatively stable rate of about 15 mm/year rather than being in a stage of acceleration under the protection of anchored concrete beams and other defense structures at its toe. Available data suggest that engineering measures can control the independent landslides that together constitute the huge Huangtupo mass, which will avoid the need for costly relocation of thousands of people. [ABSTRACT FROM AUTHOR]

In a recent discussion by Rashida and Singh (Rock Mech Rock Eng, 2023) regarding our paper (Tan et al. Rock Mech Rock Eng 56:7599–7617, 2023) investigating the thermal effects on non-Darcian flow within heated rock fractures, several points were raised. They argued that the temperatures and durations in our experiments may not induce thermal expansion in fractured rock due to low thermal expansion coefficients. Additionally, they highlighted potential water phase changes during heating and recommended precautions, such as pre-heated water and confining pressure, which were not implemented in our experimental setup. In response, we provide further clarification. Firstly, concerning heating time, our focus is on temperature-induced alterations in fracture geometry during the heating process rather than after temperature stabilization. Secondly, our detailed analysis of the coefficient of thermal expansion for granite specimens confirms that thermal expansion does lead to fracture closure within the imposed temperature range, affecting flow characteristics. Lastly, considering the aims of the study, precautions against water phase changes were not implemented, but the potential water phase changes had a negligible effect on our results due to the low temperatures employed and the short water residence time in the fracture. In summary, we maintain the methodological soundness of our experimental setup and the appropriateness of the obtained results in alignment with the objectives of our study. The discussion and this response are helpful to further clarify our experimental results and eliminate potential ambiguities. Highlights: Temperature-induced alterations in fracture geometry during the heating process are noteworthy. Even minor fracture closure resulting from thermal expansion markedly influences flow behaviors. Low test temperatures render potential water phase changes inconsequential to our findings. [ABSTRACT FROM AUTHOR]

Water flow through fractured rocks in high-temperature settings is relevant to many subsurface geo-energy engineering projects including geothermal energy extraction, hydrocarbon production, and nuclear waste disposal. However, existing studies have either focused only on flow process within fractures at room temperature or on the thermal effect on fracture permeability. As a result, how and to what extent rock temperature affects the flow behavior in rock fractures remains poorly understood. Herein, we report an experimental study of the heated flow behavior in rock fractures at steady-state elevated temperatures under sequentially increasing flow rates. We find that rock temperature greatly affects the flow behavior within the fracture via two mechanisms: water properties variations and fracture closure. The former reduces the flow resistance, while the latter both reduces the effective hydraulic aperture and enhances the inertial effect. The more heterogeneous the initial aperture distribution is, the more significant the effect of the temperature-induced fracture closure on the flow nonlinearity will be. By combining the Forchheimer equation with water temperature measured at the fracture inlet and outlet, we quantitatively evaluated the effect of these two mechanisms on rock fracture permeability and flow nonlinearity. Finally, we develop an empirical expression for the critical hydraulic gradient of the fracture at different temperatures based on the nonlinear flow model for room-temperature fractures to quantify the emergence of non-Darcian flow. The findings from the present study are expected to shed insight into the prediction and evaluation of fluid flow within deep subsurface fractured reservoirs. Highlights: Physical mechanism of thermal effect on water flow in heated rock fractures is revealed experimentally. Thermal effect promotes non-Darcian flow by changing water properties and inducing fracture closure. A parametric model to predict onset of non-Darcian flow in heated fractures is proposed. [ABSTRACT FROM AUTHOR]

Earthquake waves influence rock toppling stability, and the effects of local earthquake propagation and topographic also affect slope deformation. Detailed engineering geology conditions of slopes are obtained and a geomechanical characterization of rock topplings is performed. To study the input earthquake waves and slope interactions, a dynamic analysis is performed using the UDEC 4.0 discrete element method (DEM) numerical code under viscoplastic conditions. The earthquake signals are representative of different peak ground acceleration, Arias intensities, and frequencies, and are used in the study of different rock topplings with different height, slope angle, and strata dip angle. The derived outputs are processed for the earthquake propagation study and to assess the induced deformation mechanisms in terms of resulting displacements, plastic zone features, and deformation mode. The results prove that an interaction exists between stratigraphic and topographic effects on earthquake wave propagation, and that these effects cannot be assessed independently. The obtained results describe the effect of topography and geological settings in rock topplings, amplifying or de-amplifying earthquake ground motion, and demonstrate that the tensile state dominates at the slope surface but evolves with depth. A shear state dominates at the toe or in the deep part of rock topplings. The rock toppling deformation mode may develop into a composite of tension fractures at the crest and sliding at depth. Compared with the static scenario, under earthquake load, tensile deformation evolves over a larger area at the crest and develops a shear zone at the toe and in the substrata. The necessary earthquake-induced toppling conditions are discussed, and the UDEC 4.0 DEM method and conventional pseudostatic approach are compared. This study shows there are a broader range of deformations inside the slope. [ABSTRACT FROM AUTHOR]