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

Rapid long-runout landslides always cause extensive damage to lives and properties, and the deposit characteristics of landslides play an important role in revealing the evolution and transport mechanism. Several intensive fieldworks were conducted at the Jiweishan landslide region in Chongqing, China to investigate the deposit features, including the motion characteristics, retention of stratigraphic sequence, inverse grading, and thickness distribution, which later helped in the calibration and setting of the numerical modeling. Based on the discrete element method (DEM), the effects of simulation parameters (friction coefficient, volume, and fall height) on the maximum travel distance and deposit area of the landslide were assessed, taking account into the joints network developed in rock mass, respectively. Sensitivity analysis was performed according to numerical data, and the calculated relative sensitivity (RS) values suggested that all parameters had an impact on the travel distance of rapid long-runout landslides, and the sensitivity could be listed in the following order of most to least sensitive: volume (RS = 0.83) > fall height (RS = 0.23) > friction coefficient (RS = 0.14). [ABSTRACT FROM AUTHOR]

This paper presents a new framework for characterizing landslide deformation. Here, the deformation of a landslide is interpreted as a summation of three components: rigid deformation, within-mass deformation, and residual deformation. On the basis of the monitored data of the landslide deformation, these three components may be characterized separately: the rigid deformation is simulated by a summation of a trend term and a periodic term, the within-mass deformation is simulated by a high-order polynomial model, and the residual deformation is simulated by a conditional random field model. In particular, the characterization of the residual deformation, the third component of the landslide deformation, with the random field allows for a probabilistic assessment of the landslide deformation in the face of geological uncertainties. With the proposed framework, the evolution of landslide deformation in both geometric and time domains may be established, which allows for an assessment of the sliding mechanism of the landslide. Further, evolution in the geometric domain may allow for an assessment of the serviceability of infrastructures in the landslide area. To illustrate this new landslide deformation characterization framework, a case study of the Yu-Kai highway landslide in Guizhou, China is presented, through which the effectiveness of the proposed framework is demonstrated. [ABSTRACT FROM AUTHOR]

Data from in situ monitoring of displacement is of fundamental importance, not only in hazard assessments, but also for understanding the deformation mechanisms of landslides. However, acquiring reliable and continuous displacement data from complex landslides is often a problem because of the high cost of instruments and maintenance. Among more than 250 dangerous landslides monitored in the Chinese Three Gorges reservoir area, the most systematic and complete monitoring data have been obtained from the Shuping landslide. A ten-year record of GPS displacements measured in eight different locations, plus rainfall and reservoir level data, are utilised to identify the movement characteristics and causal factors of the Shuping landslide. The cumulative displacement curves show a series of abrupt increases that occur every year and are separated by periods of steady, slower deformations. The maximum cumulative displacement that occurred during the ten-year monitoring period was 4.7 m at site SP-2. The maximum displacement rate was 35 mm/day, which was observed on June 13, 2012 at site ZG86. Causal factors of the Shuping landslide are identified through qualitative comparisons of the monitoring data and cross-examined by grey correlation degree analysis. The results show that reservoir water level drawdown is the main factor accelerating the movement of the Shuping landslide, with heavy rainfall playing a subordinate role. The proposed use of field data and analytical methods has the potential for providing procedures and solutions for the interpretation of landslide monitoring data. [ABSTRACT FROM AUTHOR]

The time-dependent soil creep behavior affects the strength and deformation of the shear zone in landslides. Limited studies have been carried out on the undisturbed soil samples from the deep shear zone due to the difficulties in obtaining them. This problem is investigated using a case study of the well-known Huangtupo landslide, which is the largest landslide in the Three Gorges Reservoir area of China. The creep properties of the undisturbed shear zone were studied using triaxial creep testing. Two creep stages (the primary stage and the attenuation secondary creep stage) were observed, which were characterized by a creep rate that approached zero, instantaneous deformation and the development with a constant speed. The long-term shear strength of the shear zone was calculated based on the test results. The creep stages and long-term shear strength are significantly different from those of direct creep tests of reconstituted shear zones due to the influence of the confining pressure and coarse particles. The Computerized Tomography (CT) scanning technique was also applied, and the results showed clear rotation of some coarse particles in the middle parts of the samples, which was reflected by their shapes. The changes in particle position were more significant at the bottom of the sample. Based on these results, an empirical constitutive model was proposed to describe the relations among stress, strain and time, and this model fits the experimental data well. The inhomogeneity of the undisturbed soil samples leads to different creep properties from those in ideal theoretical models; therefore, new stochastic constitutive models should be explored and developed for further studies. [ABSTRACT FROM AUTHOR]

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

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

The Huangtupo landslide is the volumetrically largest, most complex, and economically most significant landslide in the Three Gorges Reservoir Region. Detailed information about the character and dynamics of this tractive landslide is available because of access provided by a unique, 908-meter in situ research tunnel, augmented by long-term data provided by an extensive monitoring system for ground water levels, rainfall, and in situ deformation. Three major rupture surfaces plus 12 interlayer sliding zones (weak layers) were recognized during tunnel excavation, which also provided access and samples that establish a complex, multistage deformation history. Data from the in situ monitoring system shows that the toe of the landslide is creeping at a steady annual rate of about 25-30 mm, but at a slower rate of about 12 mm/year near the crown. However, the monthly creep rates are variable, being highest during May-August when rainfall is heavy and reservoir levels are low. Displacement-depth curves in the HZ6 borehole inclinometer establish that the creep of Slump Mass I# is most rapid above a depth of 37 m, where a major rupture zone occurs immediately above bedrock. Engineered defense structures along the toe of Huangtupo landslide can improve its stability to some extent. The effect of rapid changes of the reservoir level on landslide stability should be considered in reservoir management. [ABSTRACT FROM AUTHOR]

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

A field investigation of the Huangtupo landslide in the Three Gorges Reservoir area, China, indicated that the particle-size distribution—characterized by an index termed the fractal dimension—varied along the main sliding direction: the fractal dimension tended to increase in this direction. A preliminary study of the spatial variability of the slip zone based upon the fractal dimension was performed. Remolded soil samples with various fractal dimensions obtained from the Huangtupo landslide were prepared for laboratory testing that was carried out to determine the effect of the fractal dimension on the micro and macro behavior of the soils. The microstructure of each soil sample was determined using scanning electron microscopy, while its macromechanical properties were evaluated via consolidated undrained triaxial tests. The results showed that there were close relationships of the fractal dimension with the microstructure, stress-strain behavior, and shear strength. The test results were also consistent with the results of the field investigation of the Huangtupo landslide. Thus, the fractal dimension can be used as an indicator of the spatial variability of the slip zone of a landslide. [ABSTRACT FROM AUTHOR]

The deformation and failure mechanism of landslides caused by reservoir water operations is a significant problem that is being addressed by researchers. The Xiaochatou Landslide in the Wudongde Reservoir area is taken as an example for the performance of centrifugal model tests under gravel conditions with the rapid drawdown of the reservoir water level. The data concerning the displacement and pore water pressure during this process show that the Xiaochatou Landslide, which is a complex landslide containing a shallow slide mass, middle slide mass and deep slide mass, is extremely sensitive to the rapid drawdown of the water level. The centrifuge tests show that the shallow slide mass will fail and that the middle slide mass will suffer a large displacement after a rapid decrease in the reservoir water level. Furthermore, the Xiaochatou Landslide exhibits the characteristics of retrogressive failure. [ABSTRACT FROM AUTHOR]