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The soil parameters for large, complex landslides are typically derived from incomplete information based on a small sample set due to budgetary constraints. This informational incompleteness results in large statistical uncertainty in landslide reliability analyses. In this article, the bootstrap technique is proposed to quantify the statistical u...
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In this paper, a new reliability model has been developed for a single system degrading stochastically which experiences soft and hard failure. Soft failure occurs when the physical deterioration level of the system is greater than a predefined failure threshold, and hard failure occurs when the instantaneous stress caused by a shock process is gre...
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... These investigations revealed that the primary sliding direction of the two landslides is approximately 340 • -350 • (NNW), with average slope angles of about 20 • -30 • . Several studies based on surface deformation and subsurface exploration have further shown that the instability of both landslides can be divided into three subzones (Fig. 2a) (Ma et al., 2019;Huang et al., 2020;Zhu et al., 2024). Specifically, the Outang landslide has a gentle slope gradient (6 • -9 • ) in Block 1 (OLB1) and steeper gradients (20 • -29 • ) in Blocks 2 and 3 (OLB2 and OLB3), with deformation primarily concentrated in OLB3 (Ma et al., 2019;Ye et al., 2022). ...
... Several studies based on surface deformation and subsurface exploration have further shown that the instability of both landslides can be divided into three subzones (Fig. 2a) (Ma et al., 2019;Huang et al., 2020;Zhu et al., 2024). Specifically, the Outang landslide has a gentle slope gradient (6 • -9 • ) in Block 1 (OLB1) and steeper gradients (20 • -29 • ) in Blocks 2 and 3 (OLB2 and OLB3), with deformation primarily concentrated in OLB3 (Ma et al., 2019;Ye et al., 2022). The Xinpu landslide has a gentle rear section with a dip angle of 5 • -8 • (XLB3), a steeper leading section (5 • -12 • , XLB1), and the steepest middle section (10 • -25 • , XLB2), with deformation mainly concentrated in XLB1 (Ye et al., 2024b;Zhu et al., 2024). ...
... 6 m 3 , as calculated by differencing the UAV-derived DEMs in 2021 and 2022 from ZY-3 DEM in 2017 (Fig. 7a, 7b). Assuming that the density of landslide material is 2,500 kg/m 3 (Ma et al., 2018;Mokhtarzadeh et al., 2022), then 4.5±0.8×10 9 kg of material surged into the lake from an altitude of 4440-4750 m a.s.l. ...
Glacial lake outburst floods (GLOFs) are a major natural hazard in high mountain regions and have caused significant loss and damage. In the past decade, two lakes (Ranzeria Co in 2013 and Jiweng Co in 2020) burst within a single river basin in the Nyainqêntanglha range of the Tibetan Plateau. These GLOFs destroyed local infrastructure and vegetation, and eroded river banks. In this study, field measurements, satellite remote sensing, and hydrodynamic modelling were used to reveal the causes, mechanisms, and flow dynamics of these events. Field surveys in 2020 and 2022 including lake bathymetry, lake shorelines, high-resolution aerial photographs, geomorphological data, and downstream damage, provided evidence to analyze the triggers and mechanisms involved in both cases. The results show that Ranzeria Co expanded by 123% in area between 1976 and 2012, and contracted by 53% in 2013 due to the outburst. The area of Jiweng Co grew by 54% from 1976 to 2020, and shrank by 57% after the dam breach. Lake levels decreased by 20.2±0.3 m in 2013 for Ranzeria Co and by 25.8±0.3 m in 2020 for Jiweng Co, corresponding to water volume losses of about 7.9×106 (68%) and 1.1×107 m3 (87%), respectively. Using the hydrodynamic model HEC-RAS, it was found that the GLOFs reached peak discharges of about 7,500 m3/s with an average velocity of 8.8 m/s at Ranzeria Co, and 5,100 m3/s with 3.7 m/s at Jiweng Co. The Ranzeria Co outburst involved a cascade of processes, including the collapse of the parent glacier, a displacement wave in the lake, and the overtopping of the moraine dam. The processes of the Jiweng Co outburst were more complex, including an unstable lateral moraine, landslides entering the lake, rising water level, dam erosion, and finally dam failure. The study provides important insights into the mechanisms of two GLOF events, which are key to assessing and managing the hazards of critical glacial lakes in the Tibetan Plateau and its surroundings.
... Thus, the GPS data strongly highlight that the landslide shows a deformational pattern characterized by a gradual increase of the displacements with the elevation. Many previous studies hold that the primarily triggering factors of the slope movement could transit from the drawdown of the reservoir water to the periodic rainfall (Guo et al., 2020;Luo and Huang, 2020;Ma et al., 2019), as it has been proved in this work. Four scatter plots in Fig. 9 (MJ01, MJ05, MJ06 and LJ13, located at O1) show that most of the statistical points are located at quadrant І, which contains those points in which the drawdown period caused relatively large displacement velocities, proving that the reservoir water destabilizes the rock mass at the front part of the landslide. ...
... Owing to the continuous and intense rainfall and the infiltration of rainwater, the sliding zone soil was saturated. Saturated conditions are commonly assumed to correspond to the most critical conditions in practical applications (Gofar et al. 2017;Ma et al. 2019b). Thus, a back analysis of the shear strength parameters of the saturated slip zone is performed. ...
The determination of shear strength parameters is a key issue in landslide treatment, and inappropriate parameter determination often leads to the failure of countermeasures against landslides. However, it is difficult to accurately determine these parameters due to the complex geological conditions and different failure models. In this study, the recommended values of the slip surface shear strength parameters for the different material compositions of a typical progressive landslide are determined using reliability methods by considering the thrust from the rear of the landslide for the first time. The reliability back analysis results and the progressive failure process of the landslide are verified via a numerical simulation. This reliability back analysis method provides an effective reference for parameter determination for similar landslides and can be applied to other types of landslides.
... The thickness of the mobilized material increases downslope from 18 to 100 m (occasionally exceeding 105 m at the toe) (Fig. 4). After a detailed investigation of the Outang landslide by several works of literature (Ma et al., 2019;Yin et al., 2016;Yang and Sai, 2019), this instability can be divided into three reactivated subzones (labeled as O1,. Each subzone shows a 'chairlike' spatial geometry featured with a gentle terrain followed by a steep terrain (Fig. 4). ...
... The material properties of both blocks matrix and fractures are listed in Table 1. These parameters were obtained from survey report developed by the Nanjiang Hydrogeological Engineering and Geological Engineering Team, Bureau of Geology and Mineral Resources, Chongqing and previous literature (Ma et al., 2019;Yang and Sai, 2019). The material densities were 2500 kg/m 3 for bedrock and 2100 kg/m 3 for landslide body. ...
... Consequently, the value of shear stiffness and normal stiffness are 3 GPa/m and 8 GPa/m, respectively. Both the survey report and previous literature (Ma et al., 2019;Yang and Sai, 2019) indicated that there is almost no difference in the mechanical properties for three subzones, thus, we set the parameters of joint friction, fracture cohesion and fracture tensile strength in each subzone are the same. The value of a res , a zero , and a max are obtained through references to other published works (Cappa et al., 2004;Guglielmi et al., 2008 ) and via tests until appropriate value are obtained to evaluate the possible failure evolution of the landslide under the combination effect of rainfall and reservoir water. ...
More than 5000 landslides have been identified in the Three Gorges Reservoir (TGR) area since the impoundment in 2003, which posed great threats to the residential houses, transportation on the Yangtze, and dam stability. This paper focuses on the evaluation of the coupled influence of rainfall and reservoir water on deformation characteristics and failure evolution of the Outang landslide (in China) based on field investigations, a statistical Pearson cross-correlation coefficient analysis, multi-technique monitoring data, and a numerical model. This instability is a reactivated ancient landslide with a volume of approximately 90 Mm³ located in the Three Gorges Reservoir. The slope behavior is featured with a short period of fast displacement and a relatively long period of semi-constant displacement rates per hydrological year, and displacements velocities quicken gradually upslope. Rainfall and reservoir water level are the main triggering factors of slope movement existing in the upper and the lower parts of the landslide, respectively. Based on the numerical results, the failure evolution of this landslide is a compounded push-retrogression-type failure process involving: a) a first rupture at the toe caused by the reservoir water level that will rapidly mobilize a second and subsequent collapses upwards (retrogression type); and b) the rock mass at the upper part will be pushed out and failed downslope (push type) due to precipitation. These results provide a comprehensive analysis of the Outang landslide, which is critical for its management, as well as for disaster prevention and mitigation of analogous reservoir-induced landslides.
... Noguchi et al., 2011;Hu et al., 2013;Zhu et al., 2016;Coblenz et al., 2018;Ng et al., 2019) and the geotechnical engineering (e.g. Most and Knabe, 2010;Luo et al., 2013;Li et al., 2015a;2015b;Ma et al., 2019;Pandit et al., 2019;Huang and Zhou, 2020). For the model uncertainty in hydrodynamic characteristics by numerical models for the aquaculture plant and its mooring system, the statistical uncertainty in the model bias factor can be quantified by the bootstrap method. ...
The aquaculture plant with a mooring system is a relatively novel concept compared with the traditional offshore structures and plenty of numerical models have been proposed to investigate its hydrodynamic behavior. In this study, the model uncertainty in hydrodynamic characteristics by several existing numerical models is estimated based on the validation data in the published researches. The traditional method is employed to calculate the statistics of the model bias factor and the bootstrap method is used to estimate the statistical uncertainty in the model bias factor due to the small sample size. In addition, the reliability analysis of mooring line is conducted considering the model uncertainty for a case study. The results indicate that the bootstrap method can effectively predict the uncertainty of the mean value and the standard deviation of the model bias factor and the model uncertainty can significantly affect the reliability of the mooring line. The bootstrap confidence interval of the reliability index can be calculated to achieve a more reasonable assessment of the failure probability for the designers. Therefore, the characterization of the statistical uncertainty in the model bias factor is of paramount importance for the reliability-based design of the aquaculture plant and its mooring system.
... Over the years, efforts have been made on slope reliability analysis to evaluate the slope failure probability (e.g., Chowdhury and Xu 1993, Chowdhury and Xu 1995, Griffiths and Fenton 2004, Wu 2015, Liu et al. 2017, Di Matteo et al. 2018, Huang et al. 2018, Dyson and Tolooiyan 2019, Hostettler et al. 2019, Li et al. 2019, Ma et al. 2019. For a soil slope, it is now recognized that the total failure probability can be larger than the failure probability induced by any individual slip surface (e.g., Cornell 1972, Huang et al. 2010, Cho 2013, Zeng et al. 2015, Metya et al. 2017. ...
As a slope may have numerous potential slip surfaces, its failure probability as a system is usually different from that of a single slip surface. Nevertheless, the system failure probability of a slope is often governed by several representative slip surfaces. How to identify the representative slip surfaces is important for system reliability analysis of soil slopes. Previous studies on representative slip surface identification mainly focus on circular slip surfaces within the framework of limit equilibrium methods; there are also relevant researches, albeit limited, within the framework of finite element/finite difference analyses based on the shear strength reduction method. By viewing the task of representative slip surface identification as a multidesign point identification problem, a barrier-based optimization method is suggested in this paper to identify representative slip surfaces of arbitrary shape based on the shear strength reduction method. A multiple starting point strategy is suggested to enhance its efficiency. For the three slopes examined in this paper, the method suggested is capable of identifying representative slip surfaces efficiently without prior assumption on their shapes.
... According to the materials and structures of the landslide, ERS experiments results, and previous studies [26,28,33], the ancient landslide consist of three independent blocks (marked blocks O1, O2, and O3). The displaced materials in each block are similar, and composed of gravel soil and fractured sandstone. ...
... The Mohr-Coulomb model was used for all the materials. The physical and mechanical parameters of the landslide are listed in Table 1; these parameters were obtained from some previous works developed by the Nanjiang Hydrogeological Engineering and Geological Engineering Team, Bureau of Geology and Mineral Resources, Chongqing, as well as previous literature [26,34]. The soil-water characteristic curve (SWCC) parameters-i.e., α, n, and m, as defined by [35]-are listed in Table 2. ...
In this study, an investigation on the formation mechanisms, deformation characteristics, and stability of the Outang landslide, composed by three independent blocks (O1, O2, and O3), is performed by integrating site surveys, multi-technique monitoring data, and numerical simulation. The results show that the formation mechanism for blocks O1 and O3 is slide-bulking, and is planar slide for block O2. These three blocks slide along the incompetent layers (ILs): IL1 is the slip surface of block O1 and O2, and IL3 is the slip surface of block O3. Furthermore, the west local fast movement zone might evolve into deep failure. The slope surface movement is step-like, characterized by the alternation of rapid displacement followed by imperceptible displacement over each hydrological year. The surface displacement velocities increased upslope. Based on the numerical simulation, both precipitation and reservoir water are believed as the major factors driving the slope behaviors, and the slope stability would be decreased gradually under the effect of the periodic variation of water level and seasonal precipitation infiltration. As a result of this study, some countermeasures of landslide and long-term monitoring are recommended.
... The reliability methods are increasingly recognised as a useful tool to quantify the effect of uncertain soil properties on slope stability analysis (e.g. Chowdhury and Xu 1993;Chowdhury and Xu 1995;Griffiths and Fenton 2004;Huang, Griffiths, and Fenton 2010;Wu 2015;Li et al. 2017;Luo and Bathurst 2018;Hostettler et al. 2019;Li et al. 2019;Low 2019;Ma et al. 2019). In general, as a slope may have numerous potential slip surfaces, sliding of the slope along any of the slip surfaces may result in failure. ...
Probabilistic methods are increasingly used to quantify the effect of uncertainties on slope stability assessment. The shear strength reduction method can be used for slope stability analysis without prior assumption on the shape of the failure surfaces, and hence is an attractive method for slope stability analysis. Since it is computationally more demanding than limit equilibrium methods, reliability analysis based on the shear strength reduction method is often considered as computationally challenging. In this paper, an importance sampling method is suggested to conduct system reliability analysis of soil slopes based on the shear strength reduction method. In the suggested method, the design points are first identified using a response surface method. Then, a sampling function is constructed centred at the design points. An efficient method is used to identify the failure samples based on the shear strength reduction method. Results from two illustrative examples show that the suggested importance sampling method is an effective and robust tool for system reliability analysis of soil slopes.
Bedrock-soil layer slopes (BSLSs) are widely distributed in nature. The existence of the interface between bedrock and soil layer (IBSL) affects the failure modes of the BSLSs, and the seismic action makes the failure modes more complex. In order to accurately evaluate the safety and its corresponding main failure modes of BSLSs under seismic action, a system reliability method combined with the upper bound limit analysis method and Monte Carlo simulation (MCS) is proposed. Four types of failure modes and their corresponding factors of safety (Fs) were calculated by MATLAB program coding and validated with case in existing literature. The results show that overburden layer soil’s strength, the IBSL’s strength and geometric characteristic, and seismic action have significant effects on BSLSs’ system reliability, failure modes and failure ranges. In addition, as the cohesion of the inclination angle of the IBSL and the horizontal seismic action increase, the failure range of the BSLS gradually approaches the IBSL, which means that the damage range becomes larger. However, with the increase of overburden layer soil’s friction angle, IBSL’s depth and strength, and vertical seismic actions, the failure range gradually approaches the surface of the BSLS, which means that the failure range becomes smaller.
