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The accurate determination of crack initiation stress (CI) is significant for understanding rock deformation and failure. In this paper, a new concept is introduced, namely the relative compression strain response (RCSR), which represents the compressive deformation of the rock before dilatancy of the rock is introduced. An RCSR-based method for determining CI is proposed and compared with existing methods, i.e., (1) the volumetric strain (VS) method, (2) the lateral strain (LS) method, (3) the crack volumetric strain (CVS) method, (4) the cumulative acoustic emission hit tangent (CAEHT) method, and (5) the lateral strain response (LSR) method. Data for the comparison are collected from 227 uniaxial compression test and 222 compression test for diverse rock types. The comparison results show that, the CI determined using the proposed method is in good agreement with that determined using the existing methods. The CI values determined using different methods are similar, at approximately 0.5 of uniaxial compressive strength (UCS). The ratio of CI to peak strength (PS) is approximately 0.55 under triaxial compression, which is greater than the CI/UCS ratio. According to the analysis of variance (ANOVA), there is no statistical difference among the existing methods. Compared with the exisiting methods, the proposed method has advantages of avoiding users judgment subjectivity Thus, the RCSR method can be employed to determine the CI under uniaxial and triaxial compression. [ABSTRACT FROM AUTHOR]

The distribution of soil pressure in landslides above anti-slide piles is a key factor in their design. The paper describes the evolution of stresses near soil-piles by testing a physical scale model during progressive loading. Displacement monitoring data on the surface of the landslide during loading discloses four main evolutionary stages: the initial stage of deformation, the uniform deformation stage, the accelerating deformation stage, and the damage stage. During initial deformation, the vertical distribution of soil pressure above anti-slide piles is sigmoidal, with the highest pressures occurring in the middle and upper parts of the slide mass. Next, during the uniform deformation stage, the soil pressure begins to assume a parabolic shape in a vertical profile, and this shape is fully realized during subsequent accelerating deformation. Finally, during the damage stage, the soil pressure relaxes to low values near the center of the slide mass, effectively inverting the parabola. Thus, the distribution of soil pressure above anti-slide piles changes in a complex manner during deformation, and these effects must be accommodated in the analysis and design of anti-slide piles. [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]

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]

The influence of wetting and drying cycles (WDC) on the strength weakening of typical rocks in soft and hard interbedded rock masses is vital to comprehend the mechanism of numerous bank slope failures in soft and hard interbedded strata induced by water level fluctuations. How WDC affect the strength of intact rocks in red stratum of the Badong Formation, a typical sliding-prone interbedded stratum in the Three Gorges area, is a topic worthy of comprehensive investigation. In this study, the effects of WDC on the physical and strength parameters of silty mudstone and silty sandstone were examined by performing a series of experiments on a total of 116 rock samples. Models of strength weakening were developed for the two rock types to express the relations between the strength deterioration coefficient (ratio of the weakened and initial value of strength parameters) and the number of WDC. The results indicate that treatment with WDC causes increases in the water absorption rate, and decreases in longitudinal wave velocity, tensile strength, cohesion and internal friction angle for both silty mudstone and silty sandstone samples with the rate of change decreasing with an increasing number of WDC; the variations in physical and strength parameters are larger for silty mudstone compared with silty sandstone; the effects of WDC on tensile strength and cohesion are higher than on internal friction angle for the studied rock types; Intergranular cracks and intragranular cracks were observed to increase with the number of WDC, evolution mode of rock microstructures was proposed, and the main weakening mechanisms induced by WDC was summarized as microcracks growth by mineral expansion and contraction, which weaken the strength of the studied rocks with the impact depending mainly on the mineral contents and microstructures in rocks. Finally, the established strength weakening models were applied in the numerical model to investigate the influence of WDC on the strength of rock mass with silty mudstone and silty sandstone interbedded layers in the Badong Formation. The obtained results provide useful guidance to reasonably evaluate the long-term stability of soft and hard interbedded bank slopes in reservoir area. • Typical rocks in a interbedded red stratum were sampled from the field. • Experiments were performed on 116 rock samples under wetting and drying cycles. • Effect on tensile strength and cohesion are higher than on internal friction angle. • Mineral expansion, contraction and dissolution induces weakening of rocks. • The test data were used to study strength weakening of interbedded rock mass. [ABSTRACT FROM AUTHOR]

Fluid flow in rock fractures is described by Darcy's law and its nonlinear extension, the Forchheimer equation in form of a quadratic polynomial. Since the nonlinearity of the Forchheimer equation, determining its key coefficient of inertial permeability (i.e., the quadratic coefficient representing inertial losses) requires a series of flow tests under different hydraulic gradients. However, how to choose the volumetric flux range for deriving inertial permeability is never scrutinized. Here we report a seemly irrational dependency of inertial permeability on volumetric flux range by massive direct numerical simulations of fluid flow in rock fractures. This variation presents traceability and is closely related to the evolution of microscale eddies and macroscale flow regimes. A concept of global inertial permeability is thus proposed from this traceable variation, which can reproduce the whole flow regime in rock fractures. Two parametrized criterion models are subsequently established for calculating global inertial permeability using the lowest cost and ensuring its accuracy: one in terms of minimum Reynolds number for practical purposes, and the other in terms of minimum eddy volume ratio for mechanistic interpretation. Further discussions indicate that the proposed global inertial permeability is of great importance to non-Darcian flow prediction and flow regime assessment. Moreover, the parameterized criterion models in the form of power-law function for determining global inertial permeability, drawn from 2D fracture simulations, can apply to 3D fractures and large-scale fractured rock aquifers. The findings and results in this study are of great significance for accurately evaluating the hydraulic conductivity of rock fractures, especially at relatively high flow rates, and are useful for many geophysical and industrial applications. • Variation of inertial permeability with flow ranges is manifested which results from evolving eddies and flow regime. • Global inertial permeability referring to stable value of the variation is proposed to reproduce the whole flow regime. • Practical and mechanistic criterion models for determining global inertial permeability are both established. [ABSTRACT FROM AUTHOR]

Dynamic behavior and failure mechanism of slope during earthquake are hot topics in geotechnical engineering community. In Tianshui area, Northwest of China, the deformation features of loess-mudstone slopes induced by earthquakes are still not well understood. The current study aims to discuss the dynamic behavior of the slope under earthquake, by performing a series of centrifuge shaking table tests and numerical simulations. The results are processed for PGA amplificatory effect study and to evaluate the earthquake induced deformation mechanism. Better agreement is obtained between the results of numerical simulations and centrifuge tests. The results indicated that the acceleration response of the loess-mudstone slope showed several amplifying characteristic: the height effect, lithologic effect and surface effect. It also proves that the displacements in the loess layer are much larger than mudstone. As the input amplitude increased, the shear plastic zone developed along a further slide surface. Tension plastic zone mainly occurred at the crest. Roughly, the regions of earthquake induced deformation state increased with the increase in amplitude of earthquake wave. Deformations occurred at the upper part of the slope. Tensile cracks evolved on the crest and the upper part of slope in loess layer, moreover, failures occurred at slope surface, and only slight deformation at slope toe. Deformations with continuous shear cracks and slope surface upheavals developed at the middle part of slope. [ABSTRACT FROM AUTHOR]