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Abstract The Observation and prediction of crack propagation are important in understanding rock behavior in engineering practice. Previous studies have focused on homogeneous and isotropic rocks, but the influence of bedding planes on rock fracture is sparingly documented. In this study, we investigate the fracturing response in uniaxial compression of artificial bedded rocks containing variable-inclination bedding planes and single structural flaws. The recorded stress-strain data and captured cracking patterns are examined together. Nine separate crack types are identified in which bedding-plane sliding and splitting are potentially new. The presence of bedding planes plays a decisive role in crack propagation. With a steepening of the bedding plane, tensile cracks initiating from the structural flaw are better able to propagate along bedding planes, and the accumulative length of bedding fractures accordingly increases. Failure transforms from a purely tensile mode to a bedding sliding mode and subsequently to a bedding splitting mode as the bedding inclination increases. Compared to pro-dip flaw tests, the fracturing of bedding planes is triggered by both the tensile and shear stress with more far-field tensile cracks initiating from bedding planes in the specimens containing anti-dip flaws. Finally, the results are applied to predict the failure mode and fracture evolution in bedded rock slopes. Highlights • Fracture evolution in artificial bedded rocks containing single structural flaws are examined. • Nine crack types and five failure modes were identified in which the bedding sliding and splitting are potentially new. • Effects of both the bedding plane and structural flaw on mechanical behavior of the bedded rock are discussed. • The experimental results are applied to predict the failure mode and fracture evolution in bedded rock slopes. [ABSTRACT FROM AUTHOR]

An approach was proposed to automatically measure the discontinuity geometric properties from a point cloud acquired using Light Detection and Ranging (LiDAR). The procedure primarily includes the following features: (Assali et al., 2016) Grid data from the point cloud was created to enhance computational efficiency for data processing and retrieval; (Barton & Choubey, 1977) A modified region growing (MRG) algorithm, which is characterized by more efficient grow criterion, was used to recognize discontinuities from the point cloud; (Cao et al., 2017) Four geometric properties from identified discontinuities were calculated based on analytic geometry; (Chen et al., 2016) Influence of threshold T on the identified results was investigated through sensitivity analysis, and threshold T was suggested to be less than the minimum normal difference among all joints and larger than 0°. Two cases (regular polyhedrons and a tunnel in the Rumei hydropower station) were taken as case studies to validate the developed approach, and calculation results have good agreement with real situations. [ABSTRACT FROM AUTHOR]

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]

Previous determinations of the optimal stabilizing pile location have generally been based on the idealized assumption of arc-shaped sliding surfaces. This assumption, however, may be inconsistent with the actual situation of most common irregular shapes, such as the step shape; as a result, determinations based on this assumption tend to involve considerable error. This paper presents a strategy, termed the local safety partitioning (LSP) methodology, for accurately determining optimal pile locations for step-shaped configurations. Instead of assuming the sliding surface to be arc-shaped, this strategy considers the actual sliding shapes. A new index termed the local safety factor is introduced for measuring the stabilities of local landslide masses, and this method employs the Swedish slice method to calculate the value of the index. The LSP methodology consists of four procedures: slicing the landslide mass into blocks, calculating the local safety factor of each sliced block, dividing the landslide mass into local partitions based on the previous step, and identifying the optimum pile position using previously identified partitions. The performance of the presented methodology is illustrated using the Jinle No. 2 landslide case for well-rounded demonstration and using the Yancun landslide case for additional validation. The results indicate that analysis of a reinforced landslide employing the LSP methodology acquires the largest safety factor and smallest deflection, shear force and bending moment on the pile body compared with any other case from a series of positions that incorporate traditional positions for arc-shaped sliding surfaces. The presented methodology provides a simple but accurate determination of the optimal stabilizing pile location for stepped sliding surfaces, although it may involve errors and unexpected limitations when applied to arc shapes and peculiar scenarios. [ABSTRACT FROM AUTHOR]

Strata consisting of massive, dipping layers of hard rock interbedded with thin, soft interlayers are common in Southwest China, and this structure is conducive to the formation of consequent bedding rockslides. The huge Jiweishan rockslide is an example that mobilized 5.6 million m 3 of massive, lower Permian limestone that was stratigraphically situated above a weak, 30 cm-thick layer of bituminous shale with a downslope dip of 21°. Field data and historical observations indicate that the rupture surface of this rockslide weakened gradually from the rear, upper part to the front. This evidence includes (1) a decrease in the thickness and areal extent of fracture-parallel calcite veinlets along the thin rupture zone. (2) the development of a wide, vertical tension fracture at the upper boundary of the slide block, about 50 years before the catastrophic failure; (3) a succession of small collapses that migrated from the upper to the lower parts of the slide block in the decade before the massive failure. This type of landslide is accordingly termed an advancing consequent bedding rockslide (ACB rockslide). An equation was developed to simulate the mechanical behavior of the rupture surface as a function of position and time. Finally, a computational model that incorporates this equation was used to simulate the evolutionary history using realistic mechanical parameters. The simulation results show how the size of an upper “driving block” progressively enlarges at the expense of a lower “ locking block” that restrains the slide mass, until the locking block becomes so small and weak that failure occurs. Good agreement between the simulation results and field data support the proposed evolution model, including the calculated size of the locking block prior to failure and the width of the upper tension fracture. [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]

This paper compares the performance of five popular machine learning methods, namely, particle swarm optimization–extreme learning machine (PSO–ELM), particle swarm optimization–kernel extreme learning machine (PSO–KELM), particle swarm optimization–support vector machine (PSO–SVM), particle swarm optimization–least squares support vector machine (PSO–LSSVM), and long short-term memory neural network (LSTM), in the prediction of reservoir landslide displacement. The Baishuihe, Shuping, and Baijiabao landslides in the Three Gorges reservoir area of China were used for case studies. Cumulative displacement was decomposed into trend displacement and periodic displacement by the Hodrick–Prescott filter. The double exponential smoothing method and the five machine learning methods were used to predict the trend and periodic displacement, respectively. The five machine learning methods are compared in three aspects: highest single prediction accuracy, mean prediction accuracy, and prediction stability. The results show that no method performed the best for all three aspects in the three landslide cases. LSTM and PSO–ELM achieved better single prediction accuracy, but worse mean prediction accuracy and stability. PSO–KELM, PSO–LSSVM, and PSO–SVM always yielded consistent predictions with slight variations. On the whole, PSO–KELM and PSO–LSSVM are recommended for their superior mean prediction accuracy and prediction stability. • The performances of machine learning methods depend on the selected evaluation index and reservoir landslide case. • Using single prediction accuracy for evaluating the superiority of machine learning methods may be unreliable. • PSO-KELM and PSO-LSSVM are recommended for their superior mean prediction accuracy and prediction stability. [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]

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]

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]

Rock discontinuities are essential for the mechanical behavior and stability of rock mass. Previous approaches for characterizing discontinuities either rely on limited handcrafted features (point normals, point curvatures, point densities, and so on) or fail to classify discontinuities, making them unsuitable for complex and large-scale scenes. To cope with these problems, an end-to-end point-based deep learning method that can automatically learn rich and high-dimensional features and classify discontinuities was developed in this study. Firstly, a roadcut and part of a natural slope were selected to train the developed network and assess its performance. Subsequently, the trained network was used to classify the remaining part of the slope. Finally, the "Density-Based Scan Algorithm with Noise" (DBSCAN) and principal component analysis (PCA) algorithms were employed to extract individual discontinuities and calculate their orientations. The two cases achieved a global accuracy (GA) of 97.25% and 94.56%, respectively, and a mean intersection over union (MIoU) of 93.77% and 88.66%, respectively, indicating the excellent performance of the network. Meanwhile, the average error in dip angle and dip direction was 0.67° and 3.33°, respectively, proving the characterization ability of the developed method was satisfactory. Furthermore, the presented method exhibits strong robustness and the potential to characterize large-scale rock discontinuities with noise. This method facilitates the application of deep learning in geosciences and provides geologists and geological engineers with a new idea for rock discontinuity characterization. • A point-based deep learning method for discontinuity characterization was developed. • The method can process point cloud directly without handcrafted features. • It can extract rich and high-dimensional features and classify discontinuities. • It has huge advantages in mapping discontinuities in complex and large-scale scenes. [ABSTRACT FROM AUTHOR]

Classifying excavation-induced slopes considering the arching effect and understating the features are crucial for determining the appropriate designs for excavation, assessing the long-term behaviors of excavations, and identifying potential failure modes. The objective of this study is to establish a classification system for excavation-induced slopes and to identify the features and applications of each slope. A series of physical model tests were carried out to investigate the deformation and failure behaviors of slope under different conditions. Assisted with the monitoring of earth pressure cells, digital and high-speed cameras, the deformation and failure characteristics were analyzed through particle image velocimetry (PIV) analysis. The results show that the slope models can be separated into three types: "shear plane arching" slope; "partial arching" slope; and approaching "full arching" slope. During the prefailure process, unyield zone ratio decreases from "shear plane arching" slope to "particle arching" slope to approaching "full arching" slope, while the yield zone ratio and interaction zone ratio increase. In the postfailure, the "full arching" slope can create higher initial kinetic energy. The classification and features of the excavation-induced slopes helps to supply engineers with the information for guiding the operation at sites. • Classification system for excavation-induced slopes is built. • Models can be separated into three types: "shear plane arching", "partial arching", and approaching "full arching" slope. • Unyield zone ratio decreases from "shear plane aching" slope to "particle arching" slope to approaching "full arching" slope. • "Full arching" slope can create higher initial kinetic energy in the post failure. [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]

• New energy-evolution perspective is provided on failure mechanism of b4 mudstones. • Energy-parameters estimation methods under cyclic loading-unloading are presented. • A parameter to measure proportion of CDE is introduced, which is defined as CDE/TAE. • Influence of stress path on mechanical properties and energy evolution is revealed. Purplish-red mudstones from Section Four of the Badong Formation are broadly distributed in the Three Gorges Reservoir area (TGRA) and exhibit special characteristics distinct from the mudstones elsewhere. This paper investigates the failure mechanism of such mudstones from a new perspective of energy evolution. Initially, the complete failure process under three stress paths (i.e., loading, unloading, and cyclic loading-unloading) is monitored, and the related data are acquired. Methods to estimate the energy parameters (i.e., total absorption energy (TAE), cumulative dissipation energy (CDE), and elastic strain energy (ESE)) under cyclic loading-unloading conditions are presented. Two new parameters, namely, the proportion of CDE (PCDE) and proportion of elastic energy dissipation (PEED), are introduced. Using the data, the mechanical properties and energy properties are analyzed, and the energy evolution is revealed. The results show that the failure mechanism under the three stress paths is different from an energy evolution perspective. The mechanical parameters deteriorate under unloading in comparison with those under loading. The increase in the CDE is similar to that in the TAE, and the ESE-strain relationship features a step-shaped rise. For cyclic loading-unloading, the TAE and the PCDE nearly linearly increase with cycle times. This work provides a new perspective on the failure mechanism of the purplish-red mudstones from the TGRA. [ABSTRACT FROM AUTHOR]

The impoundment of the 660-km long reservoir behind the huge Three Gorges Dam, the world's largest hydropower station, increased regional seismicity and reactivated severe geohazards. Before the reservoir filling was initiated in 2003, the region had approximately two earthquakes per year with magnitudes between 3.0 and 4.9; after the full impoundment in 2008, approximately 14 earthquakes per year occurred with magnitudes between 3.0 and 5.4. In addition, hundreds of landslides were reactivated and are now in a state of intermittent creep. Many landslides exhibit step-like annual pattern of displacement in response to quasi-regular variations in seasonal rainfall and reservoir level. Additional problems include rock avalanches, impulse waves and debris flows. The seriousness of these events motivated numerous studies that resulted in 1) Better insight into the behavior and evolution mechanism of geohazards in the Three Gorges Reservoir Area (TGRA); 2) Implementation of monitoring and early-warning systems of geohazards; and 3) Design and construction of preventive countermeasures including lattice anchors, stabilizing piles, rock bolts, drainage canals and tunnels, and huge revetments. This paper reviews the hydro-geologic setting of TGRA geohazards, examines their occurrence and evolution in the past few decades, offers insight learned from extensive research on TGRA geohazards, and suggests topics for future research to address the remaining challenges. [ABSTRACT FROM AUTHOR]

The uncertainty involved in the interpreted geological model may be categorized as the stratigraphic uncertainty and the properties uncertainty. Note that although the influence of the properties uncertainty on the behavior or performance of the geotechnical system and the geotechnical design has been extensively reported in the literature, the studies that address the stratigraphic uncertainty are limited. This paper presents a study regarding the influence of the stratigraphic uncertainty on the behavior of the geotechnical system and the geotechnical design. In which, the uncertainty in the stratigraphic configuration is characterized using the stochastic Markov random field-based approach with a large number of potential stratigraphic realizations. With these stratigraphic realizations as inputs, the influence of the stratigraphic uncertainty on the behavior of the geotechnical system is evaluated in a probabilistic manner; then, the design of the geotechnical system is formulated as a bi-objective optimization-based problem that considers the design safety and the cost simultaneously. To demonstrate the effectiveness of the proposed probabilistic analysis and design approach, the problem of designing stabilizing piles in a slope consisting of multiple strata is studied. The parametric study is further conducted to analyze how the probabilistic analysis results are influenced by the pile parameters and how the probabilistic design results are influenced by the additional boreholes. • The uncertainty in the stratigraphic configuration is characterized with the stochastic Markov random field-based approach. • The influence of the stratigraphic uncertainty on the behavior of the geotechnical system is studied. • The influence of the pile parameters on the probabilistic analysis results of the reinforced slope is studied. • The superiority of the proposed probabilistic analysis and design over the deterministic approaches is demonstrated with an illustrative application. [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 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]

Reliable particle measurements are essential when investigating the size and shape of particles in various fields of study, including engineering geology. Common methods to determine the morphology of particles, such as 3D laser scanners, are typically expensive or require extensive preparation. Therefore, a setup-friendly, low-cost, and accurate approach is required. In this study, a practical Trick-Image-Capturing (TIC) method based on smartphone photogrammetry to obtain size and shape parameters of 3D coarse particles is proposed. The process of image acquisition and particle reconstruction of the TIC method is demonstrated. Then, the performance of the TIC method is comprehensively assessed under various conditions using a 3D laser scanner, including smartphone quality, particle shape, shooting method, and postprocessing software. An optimal setting of the TIC method is selected through the cloud-to-cloud distance. Finally, the size and shape parameters of 32 coarse particles using the TIC method are also evaluated. Results show that the optimum setup of the TIC method is using a smartphone camera with a resolution above 12 MP under the ICS mode with a 30° shooting angle with Metashape postprocessing software. The root mean square error (RMSE) of cloud-to-cloud distances and the average error ratios under the optimum setup are less than 0.075 mm and 3.5%, respectively. Due to its fast image capturing process, easy setup, and low cost, the TIC method is practical and we expect it to become one of popular methods of measuring 3D coarse particles. • A practical Trick-Image-Capturing (TIC) method for measuring 3D coarse particles is proposed. • The workflow, accuracy, and best practices of the method were comprehensively assessed. • The RMSE of cloud-to-cloud distances and the average error ratios are less than 0.075 mm and 3.5%, respectively. • This method is expected to become one of popular methods of measuring 3D coarse particles. [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]

Reservoir landslide evolution is a complex multi-fields dynamic process which involves the interaction of the seepage field, stress field, displacement field and temperature field. After installing the stabilizing structure into landslide, the landslide and stabilizing structure will establish the landslide-stabilization system and lead to a more complex multi-fields evolution process under the reservoir operation. To study this complex problem, this paper designs and establishes a comprehensive in-situ multi-fields information monitoring platform which has been installed on Majiagou landslide in Three Gorges Reservoir area. The multi-fields information monitoring platform has four components: the landslide-stabilization system, the in-situ multi-field monitoring system, the data transmission and receiving system, and the database management system. The landslide-stabilization system includes Majiagou landslide and two experimental reinforced concrete piles. The in-situ monitoring system consists of landslide surface deformation monitoring system, experimental piles monitoring system and boreholes monitoring system. The landslide surface deformation monitoring system includes GPS stations and fiber lines. The experimental pile monitoring system consists of earth pressure cells around piles, stress and strain gauges on steel bars, and strain and temperature fiber sensors in piles. The borehole monitoring system includes boreholes with inclinometers, water pressure and water level gauges, fiber sensors. Therefore, the in-situ monitoring system can monitor the seepage, stress, displacement and temperature fields in the landslide, as well as the force and deformation in the experimental piles. Currently, the data transmission and management system is under construction and will be finished soon. Current monitoring results show that the landslide moves along three slip surfaces and the deformation of the experimental piles is influenced by reservoir operation. This platform can provide multi-fields data for scholars to study the evolution of landslide-stabilization system. [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]

Land subsidence, induced by the over-exploitation of groundwater resources, is becoming a huge hazard in many large cities around the world. Risk assessment of the infrastructure under the threat of land subsidence plays a vital role in urban planning and design. In this study, an integrated approach that combines the land subsidence, the ground fissures, and the elements at risk is proposed. The ground surface deformation is studied with time-series Interferometric Synthetic Aperture Radar (InSAR), and the differential settlement is assessed by an index of angular distortion. Then, the elements that are potentially affected by the land subsidence are recognized through a land use classification analysis, which is based on a synergetic use of optical and radar images using an object-based approach. Finally, the risk due to land subsidence is assessed using a risk matrix that integrates the differential settlement, the ground fissures, and the land use classification results. To demonstrate the effectiveness of the proposed method, a risk assessment of the land subsidence in the City of Xi'an, China is conducted. Our results also illustrate the advantages of the synergetic land use classification over the pixel-based classification. • An integrated method is proposed for large-scale land subsidence risk assessment. • Differential ground settlement is obtained with time-series InSAR analysis. • Elements at risk are recognized by a synergetic land use classification analysis. • A risk assessment matrix is adopted in the land subsidence risk mapping. [ABSTRACT FROM AUTHOR]

The paper presents a study on the location determination of stabilizing piles in colluvial landslides with the interbedding of hard and soft bedrocks. A double-arc model is proposed to describe the shape of sliding surface of colluvial landslides, and the corresponding slope surface can be divided into three types, namely the concave type, straight line type, and convex type, respectively. The driving force of colluvial landslides and interbedding characteristics of hard and soft bedrocks are two important factors affecting the determination of optimal location for stabilizing piles. The results indicate that the stabilizing effect of the piles mainly depends upon the hard bedrock. The effect of the location of hard layer bedrock on the pile deformation is represented by the location coefficient. It is found that the optimal location of stabilizing pile locates where both top and bottom hard layers are present; and, the location with a top soft layer is unfavorable, particularly when the hard layer has a large location coefficient. The case study of Yanguan landslide illustrates that the location of stabilizing pile is determined with the proposed method is effective, with a considerable decrease in both the displacement and internal force of the stabilizing piles. [ABSTRACT FROM AUTHOR]

The mechanical behavior of in situ sliding zone soil is unique and is significant for the state identification and prediction of landslides. This study focuses on interpreting the anisotropic deformation observed on the sliding zone soil of the Huangtupo landslide during an in situ triaxial creep test; specifically, the deformation of the A-Surface (towards 35° dip direction) of the soil cube, which points approximately to the landslide sliding orientation, is significantly large. Such anisotropy could be attributed to damaged structure, assumed as pre-existing directional cracks, of the in situ soil. Therefore, a Discrete Element Method (DEM) model containing prefabricated cracks is established to investigate the deforming behavior of compressed soil during in situ creep test on the mesoscopic scale. Results indicated that the specimen's anisotropic deformation is intimately related to the presence of prefabricated cracks. Subjected to the prefabricated cracks, microcracks generated during the loading process of the specimen initiated and developed in a directional way, subsequently forming directed cracks. Then the directed cracks tend to form a complete slip zone. However, due to the insufficient vertical load, the directed cracks were unable to coalesce, and the soil mass did not fail during the in situ creep test. Thereafter, additional load was applied in the simulation model. The directed cracks then merged and a full slip zone formed, and the soil was completely destroyed. As a consequence, the anisotropic characteristics of compressed in situ sliding zone soil can be well explained in view of the cracks development. This study may help perceive the landslide deformation characteristics and facilitate the evaluation and prediction methods of landslide stability. • Anisotropic deformation of the in situ sliding zone during compression • Formation of cracked slip zone in a compressed soil sample • Brand new recognition on the in situ sliding zone soil with prefabricated cracks [ABSTRACT FROM AUTHOR]

Due to the landslide-prone geological conditions, many landslides have occurred in the Three Gorges Reservoir Region (TGRR), most of which are slow-moving ancient landslides characterized by preexisting shear surfaces. In this study, with the purpose of making full use of reactivated residual strength to prevent and treat the slow-moving landslides, such as designing anti-slide piles, the Huangtupo landslide as a typical reactivated ancient landslide in the TGRR was selected to study the overconsolidation (OCR) effect on the reactivated residual strength of deep-seated sliding zone soil by conducting a series of laboratory ring shear tests. It was found that after a short rest of one day, the reactivated residual strength increased with the increase of OCR under a given normal effective stress, but it was lost after a small shear displacement. The overconsolidation effect on reactivated residual strength at a lower stress was more prominent than that at a higher stress. Very coarse sand with a size of 1–2 mm inside the remoulded deep-seated sliding zone soil sample exerts direct control on the reactivated residual strength, and it significantly influences the overconsolidation effect on reactivated residual strength. The results could provide a reliable scientific basis for improving the stability analysis and reinforcement measures of the slow-moving landslides in the TGRR, as well as can be applied to similar slow-moving landslides in other areas. • The reactivated residual strength increased with the increase of OCR after a short rest of one day. • The overconsolidation effect at a lower stress was more prominent than that at a higher stress. • Very coarse sand inside the soil sample significantly influences the overconsolidation effect. [ABSTRACT FROM AUTHOR]

The behavior of stabilizing piles with different embedded lengths in bedrock with a hard upper layer and a weak lower layer is examined using physical model tests. Based on the geological model of the landslide with bedrock with a hard upper layer and a weak lower layer, the pile–landslide physical model is developed and includes the data collection system, the pile–landslide model and the loading system. The real-time deformation and moment of the stabilizing pile is obtained in the process of loading at the trailing edge of the landslide for different percentages of hard bedrock. The test results indicate that the percentage of hard bedrock has a strong influence on the deformation and moment of the stabilizing pile embedded in bedrock with a hard upper layer and a weak lower layer. A higher percentage of hard bedrock can result in a greater maximum bending moment of the stabilizing pile and a smaller displacement at the stabilizing pile head, and vice versa. The results also show that 40% of hard bedrock can be considered the critical condition in bedrock with a hard upper layer and a weak lower layer. The percentage of hard bedrock has a limited influence on the deformation of the stabilizing pile when the percentage is greater than 40%. Moreover, four tests with stabilizing piles with different embedded lengths are conducted to investigate the most suitable embedded length in the bedrock with a hard upper layer and a weak lower layer. The results indicate that 28.5 cm is a reasonable embedded length for the stabilizing pile in the two-layered bedrock with a hard rock percentage of 20%. [ABSTRACT FROM AUTHOR]

The paper presents a novel optimal plane arrangement of stabilizing piles in terms of the provided half simplified flattened ellipsoid model, which can be used to describe the three-dimensional characteristics of sliding mass for colluvial landslides. By studying the friction soil arching effect between the adjacent stabilizing piles, a reasonable pile spacing model for stabilizing piles was deduced in consideration of the driving force and shear strength of sliding mass as well as the dimension of pile cross-section. The results indicate that the net pile spacing is in direct proportion to the height of pile cross-section and shear strength parameters of sliding mass, but in inverse proportion to the driving force intensity. Consequently, the net pile spacing should steadily increase from the major slip profile to the profiles near the boundaries accordingly, which can be called the non-uniformly spaced arrangement principle of stabilizing piles for colluvial landslides. In view of the scale factor and groundwater in the different cross sections of landslide, the improved formula of stability coefficient based on the Fellennius method was proposed accordingly. Furthermore, the concept of stability limit was put forward to confine the rational arrangement region for stabilizing piles; consequently, the region beyond the rational arrangement region is not necessary to set piles any more. The case study of the Erliban landslide in the Three Gorges Reservoir Region of China shows that the quantitative optimal plane arrangement scheme based on the proposed reasonable pile spacing model and stability limit only requires 25 stabilizing piles rather than 31 stabilizing piles in the conventional uniformly spaced arrangement scheme, with an obtainable savings of 19.4% in the number of stabilizing piles. [ABSTRACT FROM AUTHOR]

Excavation is one of the common triggers for slope failures. Loss of support at the toe of a slope due to mining excavation can cause unloading of geomaterials close to the excavated area and stress redistribution. The deformation behaviour of arching-type slopes is different from the deformation behaviour of common dip slopes. Therefore, it is necessary to study the deformation and failure mechanism of slopes under excavation conditions. In this study, a series of physical model tests was conducted on arching-type slopes with different slope angles and relative densities. The physical models were monitored by various instrumentation, such as a digital camera, a high-speed camera, earth pressure gauges, and a multi-smartphone measurement system. The deformation characteristics during excavation were analysed by using particle image velocimetry (PIV). The results show that the yielding area, including the arch-shaped large deformation area and upper small deformation area, and two sides of unyielding areas were clearly observed and considered features of arching-type slope deformation related to the arching effect. In arching failures, slopes with higher relative densities can generate larger initial kinetic energy. Toe failure, sliding failures, tension cracks, and bulking failure subsequently occur in the final failure. The equations for the maximum excavation width and the curve of the stable arch of arching-type slopes are verified. • A series of physical model tests on arching-type slopes was conducted. • The physical models were monitored by a digital camera, a high-speed camera, earth pressure gauges, and a MSM system. • Yielding area and two sides of unyielding areas were clearly observed in tests. • In arching failures, slopes with higher relative densities can generate larger initial kinetic energy. • Toe failure, sliding failures, tension cracks, and bulking failure subsequently occur in the final failure. [ABSTRACT FROM AUTHOR]

Physical model tests are considered to be useful tools and are widely used in landslide research. The three-dimensional (3D) surface deformation of slope models provides useful information for investigating the behaviour and mechanism of landslides. In this study, a measurement system called a multi-smartphone measurement (MSM) system was proposed and developed to measure the 3D surface deformation of slope models. This system includes nine identical smartphones, a USB hub, a control software package, and some postprocessing software. A series of high-quality images were simultaneously captured through the hardware devices and subsequently processed by using postprocessing software including 3D reconstruction and particle image velocimetry. A comparison with the results of a laser scanner was performed, and the performance of the MSM system was tested in two static models and one dynamic slope model. The system's accuracy was assessed using the root mean square error (RMSE) of the cloud-to-cloud distance. The results show that the accuracy of the MSM system for both the static and dynamic models is less than 1.1 mm. A short-period, low-cost, and easy-to-build system with millimetre accuracy has the potential to become a popular approach for measuring slope models. In addition, the performance of the MSM system is illustrated in three example applications. • A multi-smartphone measurement (MSM) system was demonstrated to measure the 3D shape and deformation in slope model tests. • The MSM system consists of nine smartphones, a USB hub, a computer, a control software package, and some postprocessing software. • The accuracy of the MSM system for both the static and dynamic slope models is less than 1.1 mm in the assessment tests. • The MSM system with short-period, low-cost, and easy-to-build has the potential to become a popular approach for measuring slope models. [ABSTRACT FROM AUTHOR]

Two artificial intelligence models-backpropagation neural network (BPNN) and support vector machines (SVM)-were created to investigate the effects of mesostructure characteristics on the shear mechanical behaviors of rock joints. This was achieved through learning training samples for the evaluation of the five basic geometrical parameters sensitivity (i.e., slope angle, horizontal orientation, elevation difference, curvature, and aperture distribution), and for determination of the shear failure regions when rock joints were subjected to low-normal and shear loads. First, the digital elevation models (DEMs) of rock joints were produced through point clouds collected using a laser scanning system. Five geometrical parameters were specified as the inputs for the artificial intelligence models, and an approach was developed to calculate the 3D aperture distribution using a point cloud registration algorithm. Shear failure regions were considered as the outputs, which were extracted from images taken after direct shear testing via the global threshold algorithm. Secondly, BPNN and SVM models were employed in order to establish relationships between the geometrical parameters and shear failure areas by machine learning on training samples. Thirdly, the information value (IV) algorithm was used to verify the two trained models. Results showed that the BPNN and SVM models made acceptable determinations of the shear failure areas, which corresponded to the real situation. The predictions from the BPNN and SVM models were more accurate than those from the IV algorithm. Furthermore, shear failure regions depended primarily on the aperture distribution of rock joints during the shearing process, followed by horizontal orientation, elevation difference, and then the slope angle. The effect of parameter curvature on shear failure was less than the other four parameters. • Two AI algorithms (BPNN and SVM) were used to determine the shear failure regions. • Five geometrical parameters were extracted from point clouds as the input parameters. • 3D aperture distribution was calculated via the feature-based registration algorithm. • Weights of five input parameters were estimated through trained BPNN and SVM models. [ABSTRACT FROM AUTHOR]

Effective detection of groundwater in landslide areas is crucial for landslide monitoring. The magnetic resonance sounding (MRS) method is a geophysical technique that can directly detect groundwater. However, its application in landslide groundwater monitoring is often hindered by the complex topography of landslides. This paper presents an MRS framework that accounts for the impact of landslide topography on groundwater detection. The framework includes the use of drone photogrammetry to obtain high-precision topography data and real-time kinematic equipment to acquire the coordinates of key points along the MRS coil. A three-dimensional finite element model is then constructed to calculate the alternating magnetic field generated by the MRS coil and the kernel function required for MRS inversion. Two typical landslide topography models—terrace and gully—are constructed and analyzed using numerical simulations. The results indicate that landslide topography significantly impacts the quality of groundwater information retrieved by MRS in both one-dimensional and two-dimensional inversions, affecting the accurate detection and identification of infiltration surfaces, sliding zone water, and bedrock surfaces. If accurate topography data are obtained and appropriate kernel functions are calculated, the accuracy of the inversion can be greatly improved. An example of using the MRS method to detect groundwater in a complex landslide in the Three Gorges Reservoir area of China is then presented. The MRS inversion results that consider landslide topography are confirmed using borehole data, electrical resistivity tomography detection results, and on-site drainage tunnel investigations. The water-content distribution inside the landslide body is obtained, providing information helpful to define sliding zones in multi-level landslides. The proposed landslide MRS detection framework makes it possible to apply MRS methods to the detection of landslide groundwater distribution, analysis of seepage fields, and discrimination of landslide geological structures. • Landslide topography significantly affects the quality of groundwater information retrieved by MRS. • Obtaining accurate topography data and calculating appropriate kernel functions improve MRS inversion results. • MRS field work on a complex landslide is validated by borehole data, ERT, and on-site drainage tunnel investigations. [ABSTRACT FROM AUTHOR]

Unmanned Aerial Vehicle (UAV) technique has been widely utilized in geohazards assessment. In this work, the effectiveness of the UAV photogrammetry in the remote sensing and assessment of the landslide behavior is demonstrated through a case study of a landslide that occurred in Guizhou, China on 10 June 2018. The post-landslide assessments were conducted through a field investigation by a team of experts; and, two UAV photogrammetry-based surveys were carried out. On the basis of a detailed inspection of the high-resolution aerial photographs collected from the UAV photogrammetry and historical satellite imagery, subsurface stratigraphic configuration revealed from borehole explorations and the local rainfall data collected, the failure mechanism of this landslide is investigated. The occurrence of this landslide is probably attributed to the combined influence of the long-term rainfall and the engineering activities at this site. An automatic landslide cracks recognition model, which is based on the deep learning-based image recognition technique of RetinaNet, is further developed to map the cracks at the landslide site. The effectiveness of this automatic crack recognition model is validated through quantitative comparisons between the landslide cracks recognized and the field survey results. Based upon the landslide cracks identified on two different dates after this landslide event (by the field survey and automatic crack recognition model) and the subsurface displacement revealed from a drilled hole, the evolution behavior of this landslide is analyzed. The results show that the stability of this landslide was not achieved during the first slide in June 2018 and the limit of the landslide was increased much from June to November 2018. In such a situation, the elements at risk in the zones that are potentially impacted by this landslide are identified (with the aid of the UAV images collected), and a preliminary consequence assessment is conducted. • The failure mechanism of a landslide in Guizhou, China is investigated. • An automatic landslide cracks recognition model is developed using RetinaNet. • The landslide behavior is studied based on the cracks recognized on two dates. • A UAV images-based preliminary assessment of the landslide consequence is made. [ABSTRACT FROM AUTHOR]

The shear mechanical behaviour of slip zone soil is of great significance for the stability analysis of landslides. Based on the shear deformation-failure characteristics of slip zone soil and the statistical damage theory, a shear constitutive model is proposed to describe the shear stress - displacement relation of slip zone soil. Parameters in the proposed model have clear physical-mechanical meaning, and can be easily obtained by shear tests. The shear constitutive model is verified by comparing model results with ring-shear test results on the slip zone soil from the Huangtupo landslide in the Three Gorges Reservoir Area of China. It reveals that the model is capable of capturing the salient behaviour of the slip zone soil, such as the pre-peak and post-peak deformation characteristics. Moreover, utilizing limited ring-shear test data under given normal stresses, shear stresses at various shear displacements under untested normal stress are available by this model. Finally, a dynamic evaluation method of landslide stability, which incorporates the landslide displacement by presented constitutive model, is proposed and applied to analyze the stability of the Riverside Slump II# of the Huangtupo Landslide. • A new shear constitutive model is proposed to describe the mechanical properties of slip zone soil. • A set of ring-shear test results on the slip zone soil from an active landslide are well simulated by the model. • The proposed model is capable of predicting the shear stress - shear displacement curves. • A dynamic evaluation method of landslide stability is proposed. [ABSTRACT FROM AUTHOR]

The impact angle is an important but understudied factor that exerts a significant control on the propagation of granular flows. To investigate the influence of the impact angle on the motion and deposition of granular flows, flume experiments and numerical simulations were performed using impact angles ranging from 0° to 70°. Three-dimensional laser scanning and image analysis were employed to collect structural and kinetic information on these granular flows. Moreover, the evolution of the energy components of the granular flows was investigated at selected monitoring points and entire sliding mass using numerical simulations. A lower-velocity region in the middle portion of granular flows was observed in all cases. The area and shape of this region were found to be greatly influenced by the impact angle. An energy transfer from the middle and rear regions to the front of the granular flow was also observed, mediated by particle collisions. As a result, fluctuations in the velocity and energy of the particles in front region occurred, which in turn resulted in longer travel distance. The direction of movement and the travel distance changed when the granular flows encountered an obstacle along the horizontal chute. From the macroscopic point of view, the travel distance decreased as the impact angle increased. However, individual particles - especially in the front region - could travel longer distances even in the case of large impact angles owing to the collision-mediated energy transfer. • Noncontact measurement was used to study the motion and deposition of granular flows • A lower-velocity region in the middle portions of the granular flows was observed • The overall travel distance decreased with the impact angle • Collisions in the front region caused significant fluctuations in velocity and energy • Particles in the front region could travel long distances due to the energy transfer [ABSTRACT FROM AUTHOR]

Assessing the influence of the impact pressure exerted on surrounding rock mass by potential debris flows is one of the challenges in a mountain tunnel construction project. This paper proposes an effective mathematical model for the assessment of impact pressure exerted by debris flows on obstacles. The characteristics of the new model are analyzed, and the parameters determination method for the new model are deduced. Also, a new method for dynamic reliability analysis of the rock mass surrounding tunnels is proposed and is constituted into three key steps. First, by inputting impact pressure of debris flows generated by the aforementioned new model, the FLAC3D is used as the dynamic analysis engine to obtain the time-varying stress distribution of surrounding rock mass during the impact of debris flow. Second, the factor of safety (FOS) contours of surrounding rock mass are generated based on element states using the maximum tensile stress criterion and the Mohr-Coulomb yield criterion. Third, by using the time-varying contours of the FOS, a failure probability and a reliability index are obtained from a reliability perspective. A case study shows the complete analysis process and confirms the effectiveness of the above methodology. In sum, this paper provides new ideas, new methods, and a reference example for evaluating the influence of dynamic impact exerted by debris flows on the rock mass surrounding tunnels. • A novel mathematical model is proposed for the assessment of impact pressure exerted by debris flows on obstacles. • A new method is proposed for dynamic reliability analysis of the rock mass surrounding tunnels. • The instantaneous factor of safety (FOS) of each element of the rock mass surrounding tunnels is applied based on the maximum tensile stress criterion and the Mohr-Coulomb yield criterion. • The failure probability and the reliability index of the rock mass surrounding tunnels are obtained based on space-time-varied stress fields. [ABSTRACT FROM AUTHOR]

Although numerical methods based on strength reduction are becoming popular in slope stability analysis, they fail to provide a distinct critical slip surface and only provide a shear band. The widely used visualization techniques for defining the critical slip surface are susceptible to subjective judgment and are inefficient for batch analysis and three-dimensional analysis. When a slope fails, the displacements on the two sides of the critical slip surface will be substantially different. Based on this observation, an automatic identification method for locating the critical slip surface is proposed. The k-means clustering algorithm is first applied to automatically separate the nodal displacements into two categories representing the sliding mass and the stable block. Then, the scatters near the separation surface are obtained by constructing the alpha shape of the sliding mass. Finally, the critical slip surface is obtained by fitting the extracted scatters. A homogeneous slope, a slope with a thin weak layer and a real landslide are used to test the effectiveness of the proposed method. The results show that the proposed method can automatically and accurately identify two-dimensional and three-dimensional critical slip surfaces. • An automatic method for identifying the critical slip surface of slopes is proposed. • The proposed method is simple and not susceptible to subjective judgments. • The proposed method can accurately identify the distinct 2D/3D critical slip surface. [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]

To better understand the shear mechanical behaviour, the information value (IV) and the fractal theory (FT) models are employed to determine the shear failure regions of rock joints under the low effective normal stress conditions. First, high density point clouds of rock joints at the initial stage (pre-shearing) were collected, using a laser scanning technology and four topography parameters (slope angle, horizontal orientation, elevation difference and curvature) were produced from point clouds, to represent the mesostructure features. Second, direct shear testing were conducted at the end stage (post-shearing), and shear striae on the rock joints were measured to assess shear failure regions, based on image segmentation. Third, by combining morphological features with experimental observations, correlation analyses are performed, to investigate the influences of topography parameters on shear failure behaviors of rock joints, based on IV and normalized weight W i. Similar findings are observed from the two algorithms, indicating that horizontal orientation has a larger impact on shear failure than the other three parameters. Furthermore, under the low normal loading, the shear failure of rock joints are more likely to occur in regions with a slope angle in the range of 30° to 40°, a horizontal orientation in the range of SE to SW (facing shear direction), an elevation difference in the range of 0.15 to 0.30 mm and a curvature in the range of −1000 to −200 mm−1 and 200 to 1000 mm−1. It is notable that the effect of normal loads level on shear failure regions should not be neglected. Eventually, a model is developed to predict the shear failure regions of rock joint and receiver operating characteristic (ROC) analyses show that shear failure determinations, based on the proposed model, match the actual situation. • Four topography parameters were produced from point clouds to represent the mesostructure features of rock joints. • Image segmentation was used to measure the shear failure regions of rock joints under low normal loads. • The relationships between the mesostructure parameters and shear failure regions were established based on IV and FT models. [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]

Abstract Geological disasters have occurred frequently in the Three Gorges Reservoir area. Therefore, the stability and failure mode research on riverside landslides has become increasingly important. Taking the toe of Liangshuijing landslide as a case study and combining the geological conditions of the Three Gorges Reservoir area, a centrifuge slope model is constructed. In addition, the fluctuation of the water level is simulated in the centrifuge model test. Based on the digital photography, laser displacement sensors (LDS), pore pressure transducers (PPT) and earth pressure sensors (E), multi-physical data are obtained. Finally, numerical simulation is carried out to analyze the stability and deformation characteristics of the slope model. The results indicate that: (1) At the water level rise stage, the model is dominated by the vertical displacement. And the horizontal displacement is much larger than the vertical displacement at the drainage stage. (2) Cracks first appear at the toe of the slope and extend to the middle and rear of the model gradually. Then, deformation occurs in the middle platform of the slope. (3) At the water level rise stage, the factor of safety increases rapidly. When the reservoir water level remains stable, the stability of the slope decreases slowly. And at the drainage stage, the factor of safety decreases first and then increases. (4) There is a significant positive linear correlation between the decline rate of the safety factor and the drainage rate over a certain test range. And the stability of the landslides on the reservoir banks would become worse gradually during the long-term cyclic operation of the Three Gorges Reservoir. Highlights • The fluctuation of the water level is simulated in the centrifuge model test. • Qualitative and quantitative method are combined to analysis the evolution of the landslide. • The failure mode and the deformation mechanism of the slope are revealed by the centrifuge model test. [ABSTRACT FROM AUTHOR]

Due to the inherent spatial variability of the geological bodies, limited boreholes (constrained by budget), and data interpretation errors, the subsurface conditions (in terms of the stratigraphic configuration and associated geo-properties) at a site are hard to ascertain, and considerable stratigraphic and geo-properties uncertainties are induced. The stratigraphic and geo-properties uncertainties could complicate the engineering design. One way to reduce the uncertainties is to adopt an optimal site exploration program under constraints. This paper presents a novel framework for optimizing the site exploration program based on a coupled characterization of the stratigraphic and geo-properties uncertainties. Within the context of the proposed framework, a conditional random field approach, recently advanced by the authors, is employed to characterize the stratigraphic and geo-properties uncertainties simultaneously. Here, the spatial correlation of stratum existence (depicting stratigraphic configuration) and that of geo-properties are estimated with a Bayesian updating scheme. Then, the 'influence zone' at the concerned site, which is often problem-specific, is selected based on a geotechnical performance evaluation. The derived influence zone can be taken as the candidate zone for boreholes. Finally, the optimal locations and depths of boreholes are determined based on the stratigraphic and geo-properties uncertainties characterized within the influence zone. To depict the effectiveness and versatility of the presented framework, two problems (i.e., a shallow foundation problem and a slope stability problem) are analyzed. • A novel framework for optimizing the site exploration program is proposed. • Site characterization and geotechnical performance evaluation are integrated. • Characterizations of stratigraphic and geo-properties uncertainties are coupled. • The spatial correlation structure is estimated with a Bayesian updating scheme. • Geological model characterization is updated in a step-by-step manner. [ABSTRACT FROM AUTHOR]

The red mudstone sediments are widely encountered in earthquake region northwestern China which is vulnerable to the occurrence of landslides. Previous studies focused on rain-induced shallow landslides. Some deep-seated landslides in red clay with a gentle inclination are still not well understood. A fatal landslide named as Zhengjiamo landslide, located in Tianshui, China, was investigated. The aim of this study was to study mechanism of shear surface development under earthquake using a series of cyclic triaxial tests. The test results of the red clay from the Zhengjiamo landslide revealed that the undrained shear strength and excess pore pressure increase with increasing confining stresses σ 3 and OCR. It is also observed that those stress–strain behaviors on the deviatoric stress, axial strain and pore water pressure, subsequent to the initial contractive response, the saturated clay exhibited dilation upon continued shearing. The dilated tendency of the clay becomes more prevalent with increasing confining stresses σ 3 and OCR during the dynamic response. The reduction of shear strength of the red clay is substantially caused by the increasing number of cycles N. Under earthquakes, the sliding zone may behave in a brittle- ductile pattern. [ABSTRACT FROM AUTHOR]

Deep-seated mudstone landslides are widely distributed in northwest China. The Zhengjiamo landslide occurred in 734 CE near Taijing, Tianshui region. It was triggered by the main shock of the historical Ms = 7.0734 CE earthquake. The earthquake also induced a wide range of landslides in this area, with hundreds of fatalities and many houses destroyed by landslide debris. Based on a detailed field survey, borehole data, and mapping, a detailed geological reconstruction of the slope was achieved and the geo-mechanical features of the claystone involved in the landslide were obtained. Using the Particle Flow Code to simulate the mechanism of the Zhengjiamo landslide, the features of the landslide dynamics were obtained using a 5-stage model. During the landslide process, the slip mass at the front and upper edges exhibited higher mobility than at the rear and bottom edges. Furthermore, the contact bond strength of the sliding body gradually weakened. The model indicates that the particle bond strength has a larger influence on the maximum runout distance and landslide debris morphology than the type of weak intercalated layers. The slip mass presented a rotational slide pattern and remained on the slip plane throughout the sliding process. Finally, the earthquake uplifted the slope toe, which prevented the slip mass from gliding. The modelled scenario provided a reasonably good fit to the actual topography, verifying the modelling results. After the historical earthquake, with the clay minerals swelling and shrinking under rainfall and efflorescence conditions, the structure of the soft rock changed, contributing to the weakening of the sliding rock mass. The landslide gradually crept and evolved to its current topography. [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]

To evaluate the possibility of utilizing commercially available devices for making joint roughness estimates, a digital single-lens reflex (DSLR) camera and a smartphone were used to reconstruct the three-dimensional models of 10 rock-joint specimens. The accuracy and efficiency were considered in investigating the performance of photogrammetry on the point clouds production and joint roughness estimation in the laboratory. Additionally, a handheld laser scanner was used in collecting high-resolution point clouds of the same specimens as reference data for evaluating the photogrammetry measurement accuracy. The interval for image capture was set at 8° with consideration for the data quality, point density, and computation time. The iterative closest point (ICP) algorithm was used to compare the surface topographies of the rock joints produced via photogrammetry and laser scanning. The point clouds generated by photogrammetry agreed with the laser-scanning results, with a small average difference (0.005 mm for the DSLR camera and 0.006 mm for the smartphone). Furthermore, two- and three-dimensional surface parameters were calculated using the three different sources of point clouds, which were in good agreement in the joint roughness estimates when comparing photogrammetry and laser scanning results. Comparative analyses revealed that both DSLR camera photogrammetry and smartphone photogrammetry can produce accurate point clouds of rock joints for roughness assessment; however, point clouds generated by the DSLR camera had higher accuracies than those generated by the smartphone. • The lens parameters determined in camera calibration differ from the nominal ones. • Interval between two camera positions affects the data accuracy and computation time. • Point clouds from photogrammetry are in good agreement with laser scanning data. • Similar estimates of joint roughness from photogrammetry and laser scanning data. • DSLR camera photogrammetry outperforms the smartphone for rock joint reconstruction. [ABSTRACT FROM AUTHOR]

Landslide early warning systems can be implemented based on the monitoring and prediction of landslide displacements. The internal mechanisms of landslides are very complex, and precise mechanistic models of landslides are difficult to obtain; therefore, data-driven models are usually applied. From the perspective of dynamic system theory, landslide development should be considered a dynamic process. Because traditional models, such as feed-forward neural networks, can only express static relationships, the applicability of these static models is quite limited in landslide prediction tasks. In our study, recurrent neural networks are established and trained into dynamic predictors of landslide displacement using a training algorithm named reservoir computing. A shortcoming of the reservoir computing algorithm is that the models will not perform well with insufficiently large training sets. Because practical landslide displacement recordings are usually quite short, interpolation techniques are employed to enhance the training of the dynamic predictors. The method proposed in this paper is applied to predict the developments of three landslides in the Three Gorges area, and the predicted values are close to the actual measurements. Improvements relative to sophisticated static predictors and basic dynamic predictors are obvious. [ABSTRACT FROM AUTHOR]

Site characterization, which aims to characterize the subsurface stratigraphic configuration and the associated geo-properties, has long been a significant challenge in geological and geotechnical practice. Due to the complexity and inherent spatial variability of the geological bodies and the limited availability of borehole data, uncertainty is unavoidable in the characterized subsurface stratigraphic configuration and the associated geo-properties. In previous studies, the stratigraphic uncertainty and the geo-properties uncertainty were characterized separately. This paper proposes a conditional random field approach for a coupled characterization of stratigraphic and geo-properties uncertainties. The spatial correlation of the stratum existence between different subsurface elements and the spatial correlation of geo-properties are characterized by two autocorrelation functions, determined with the maximum likelihood principle. With the knowledge of the spatial correlation of the stratum existence, the stratigraphic configuration can be sampled using a modified random field approach. Then, the spatial correlation of the geo-properties is updated based on the sampled stratigraphic configuration. With the updated spatial correlation of the geo-properties, the spatial distribution of the geo-properties can readily be simulated with the conditional random field theory. The effectiveness of the proposed approach is demonstrated through a case study of probabilistic site characterization of an offshore wind farm site in Taiwan. To extend the applicability of the proposed approach, a probabilistic evaluation of liquefaction potential at this site under a given seismic shaking level is performed. • A probabilistic method for characterizing the geological model is proposed. • Characterizations of stratigraphic and geo-properties uncertainties are coupled. • Stratigraphic configuration is simulated with modified random field approach. • Spatial variability of geo-properties is simulated with conditional random field. • The spatial correlation structure is estimated with maximum likelihood principle. [ABSTRACT FROM AUTHOR]