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The rationality of rockfall path analysis results is closely related to the resolution of the slope shape model. With the emergence of unmanned aerial vehicle (UAV) photogrammetry technology, which is suitable for engineering geological surveys, the modeling resolution for unstable rock slopes has gradually increased. In this paper, the process of constructing a model of unstable rock slopes based on UAV photogrammetry is improved. A method to obtain the geometric parameters of unstable rock masses by using the model is proposed. The movement characteristics required for rockfall analysis are summarized. Based on the analytical results of rockfalls, a method for setting up passive protective nets is suggested. A quantitative evaluation method is proposed for the protective effect of each protective scheme. Through a practical engineering case, two passive protective schemes (the original design and the optimized design based on the proposed method) are compared and evaluated by numerical simulation, and the actual site layout scheme is more similar to the optimized design scheme. The results show that the proposed method has a positive effect on the design and improvement of protective nets. [ABSTRACT FROM AUTHOR]

Based on stepped sliding surfaces, back edge tensile cracks divide the slope bodies into upper (region B) and lower (region A) parts. How region B affects region A, and the instability sequence and interaction relationship between regions A and B need to be further clarified. Based on this, an improved method to analyze the interaction relationship of the two regions is proposed based on the coordination relation of their accelerations. Based on system reliability theory and the possible instability sequence of regions A and B, a slope stability analysis system composed of four failure cases is constructed. Then, the limit equilibrium method and the Monte Carlo method are adopted to analyze the failure probability and dominant failure mode of the slope stability analysis system. In addition, the accuracy of the improved method is verified through comparison with existing theoretical research and discontinuous deformation analysis numerical simulation methods. The results show that with an increase in the fracture connectivity ratios (kA and kB) of the two regions, the slope stability shows a downward trend. In particular, region A is more prone to instability alone with an increase in kA. Region A is more prone to instability due to the interaction relationship because of region B with an increase in kB. In addition, with the increasing of weakening coefficients (Kc and Kφ), ratio of the joint spacing to the slope height (d/H), corresponding parameters of tensile cracks (L/H and β1) and groundwater level (Zw), region A is more prone to instability alone. In contrast, the seismic acceleration coefficients (kh and kv) aggravate the interaction relationship between the two regions and cause a sharp decrease in slope stability. Due to earthquake shaking of water, the seismic force effect on hydrous slopes is more significant with an increase in Zw. [ABSTRACT FROM AUTHOR]

Granite rocks are subjected to exogenic forces, such as tectonic stress and chemical weathering, which cause them to weather differentially, forming boulders that are common in temperate and humid regions. The presence of a large boulder on a slope can significantly impact slope stability, resulting in the formation of what is known as a solitary boulder slope. This study is dedicated to investigate the large-deformation instability characteristics of such slopes. In pursuit of this objective, our study first validates an adapted material point method through laboratory experiments. Subsequently, utilizing the inverse discrete Fourier transform theory, boulders with varying shapes were synthesized and further transformed into material point method models. Finally, the material point method was employed to analyse the impact of boulder position, shape, and incline on the large deformation characteristics of the slope. The results show that: (1) The closer a boulder is to the plastic zone of the slope, the stronger its reinforcement effect on the slope. (2) As the shape of boulders becomes more complex, the run-out distance of the slope tends to decrease, but the variability in run-out distances increases. (3) The slope plastic zone moves around the boulder, and its distribution undergoes alterations based on the boulder's shape. This study investigates the instability characteristics of large deformation in boulder slopes with varying boulder shapes, which provides a reference for the stability assessment of solitary boulder slopes. [ABSTRACT FROM AUTHOR]

Only simplified two-dimensional model and a single failure mode are adopted to calculate the ultimate pullout capacity (UPC) of anchor cables in most previous research. This study focuses on a more comprehensive combination failure mode that consists of bond failure of an anchorage body and failure of an anchored rock mass. The three-dimensional ultimate pullout capacity of the anchor cables is calculated based on the Hoek-Brown failure criterion and variation analysis method. The numerical solution for the curvilinear function in fracture plane is obtained based on the finite difference theory, which more accurately reflects the failure state of the anchor cable, as opposed to that being assumed in advance. The results reveal that relying solely on a single failure mode for UPC calculations has limitations, as changes in parameter values not only directly impact the UPC value but also can alter the failure model and thus the calculation method. [ABSTRACT FROM AUTHOR]

In practical engineering, due to the noncontinuity characteristics of joints in rock slopes, in addition to plane failure, stepped sliding failure may occur for intermittently jointed rock slopes. Especially for intermittently bedding jointed rock slopes, the correlation and difference in strength parameters between joints and rock bridges, along with the various failure modes and intermittency of rock bridges, contribute to the complexity of stepped failure modes and the unpredictability of failure regions. Based on the upper-bound limit analysis method and multi-sliders step-path failure mode, considering the shear and tensile failure of rock bridges and the weakened relationship between the strength parameters of rock bridges and jointed surfaces, by introducing the modified M-C failure criterion and the formula for calculating the energy consumption of tensile failure of rock bridges, two failure mechanisms are constructed to obtain the safety factor (Fs) of intermittently jointed rock slopes. The sequential quadratic programming method is used to obtain the optimal upper-bound solution for Fs. The influence of multiple key parameters (slope height H, horizontal distance L, Slope angle β, shear strength parameters of the rock bridge φr and cr, Dimensionless parameter u, weakening coefficients of the internal friction angle and cohesion between the rock bridges and joint surfaces Kφ and Kc) on the stability analysis of intermittently jointed rock slopes under the shear failure mode of rock bridges as well as under the tensile failure mode is also explored. The reliability of the failure mechanisms is verified by comparative analysis with theoretical results, numerical results, and landslide cases, and the variation rules of Fs with each key parameter are obtained. The results show that Fs varies linearly with φr and cr of the rock bridge and with Kφ and Kc, whereas Fs changes nonlinearly with H and L. In particular, with the increase in Kφ and Kc, Fs increases by approximately 52.78% and 171.02% on average, respectively. For rock bridge tensile failure, Fs shows a nonlinearly positive correlation with φr, cr, Kφ and Kc. In particular, with the increase in Kφ and Kc, Fs increases by approximately 13% and 61.69% on average, respectively. Fs decreases rapidly with increasing slope gradient β and decreasing dimensionless parameter μ. When Kφ and Kc are both less than 1.0, the stepped sliding surface occurs more easily than the plane failure surface, especially in the case of tensile failure of the rock bridge. In addition, rock slopes with higher strength parameters, taller heights, and greater weakening coefficients are prone to rock bridge tension failure with lower Fs, and more attention should be given to the occurrence of such accidents in actual engineering. [ABSTRACT FROM AUTHOR]

Rotational failure may exhibit in homogenous rock slopes, and the critical sliding surface of a rock slope based on the rotational failure mechanism is not a single log-spiral under nonlinear failure criterion. This work proposed an advanced nonlinear analysis method for estimating the seismic stability of homogenous slope in rock masses which is governed by the generalized Hoek–Brown failure criterion. According to the virtual power principle, the critical slope height is obtained using particle swarm algorithm. Strength reduction technique is further introduced to explore the reduction strategy of the strength parameters of the Hoek–Brown failure criterion. The outcomes indicate that the factor of safety obtained by simultaneously reducing the unconfined compressive strength σci and material parameter mi is in good agreement with the results of other methods. In addition, two cases are re-analyzed to illustrate the applicability of the proposed method, and the maximum discrepancy with existing results is about 8%. The effects of strength parameters, slope angle, and seismic quasi-static coefficients on the slope stability factor and critical sliding surface are analyzed, which shows that the seismic load and the Hoek–Brown parameters have a significant effect on the slope stability factor. There is no need to assume the expression of the potential sliding surface, which can provide theoretical support and a useful reference for the nonlinear analysis of slope stability. [ABSTRACT FROM AUTHOR]

Based on the upper bound theorem of limit analysis and variational principle, the uplift resistance of shallow horizontal anchor plates in heterogeneous soil and three-dimensional failure surface of overlying soil are investigated. The results calculated by the theoretical approach are compared with results of the existing solutions and numerical results obtained by software PLAXIS 3D to verify the validity of the variational analysis. Furthermore, the influence of the heterogeneity and nonlinearity on the uplift characteristics of shallow horizontal anchor plates is discussed. The results show that: (i) Increase in the uplift resistance and expansion of failure range are observed with decreasing nonlinear coefficient m and variation coefficient kt of soil uniaxial tensile strength as well as increasing variation coefficient kc of soil initial cohesion. (ii) Heterogeneity and nonlinearity jointly determine the shape of failure surface. This study enriches the analytical method of anchor plates and has great significance for stability and safety of anchor plates. [ABSTRACT FROM AUTHOR]

The particle shape has a significant influence on the mechanical behaviour of granular materials. Based on a new particle shape evaluation system M-A-V-L, this paper studies the effect of the M-value (a particle shape index) on the macro and micro triaxial compression behaviours of granular material via DEM modelling. Firstly, 1500 digital models of realistic ballast particles were obtained by white-light scanning. Then, the M-values of all the particles were calculated, and five groups of particles with different M-values (M = 1.5, 2.0, 2.5, 3.0, 3.5) were selected. There are five particles in each group. Subsequently, the evolution of macro and micro mechanical behaviours (such as void ratio, deviatoric stress ratio, coordination number, etc.) for samples with different M-values were analysed based on triaxial compression tests. Moreover, the relationship between M-values and mechanical behaviours for samples at both peak state and critical state were studies. Finally, by analysing the stress-force-fabric (SFF) relationship, the origin of shear strength related to M-values was revealed from the perspective of the fabric anisotropy. [ABSTRACT FROM AUTHOR]

Jointed rock landslides with stepped sliding surfaces are common in practical engineering. At present, the mechanical mechanism for the formation of a stepped sliding surface based on the tensile-shear composite failure mode of rock bridges is not clear. In addition, considering the development of secondary joints, the strength parameters of the rock bridges and joint surfaces with different weakening coefficients Kc (cohesion weakening coefficient) and Kφ (friction coefficient (tanφ) weakening coefficient) are more realistic and reliable. Based on this, considering these different weakening coefficients, a limit state analysis model of jointed rock slope stability with a stepped sliding surface based on tensile failure and tensile-shear composite failure modes of rock bridges is constructed. The influences of key parameters on the slope stability are investigated. The results show that the existence and different failure modes of rock bridges have significant influences on the slope stability. The dimensionless parameter u (reflecting the contribution of the tensile strength of rocks), Kc, and rock bridge angle β3 have significant influences on the jointed rock slope stability. When β3 is a large value, u has a significant influence on Fs. Fs decreases nonlinearly with an increase in Kc and increases linearly with an increase in Kφ. Under the tensile-shear composite failure mode, when tensile force is dominant, Fs relatively increases; when shear force is dominant, Fs relatively decreases. Therefore, the inconsistency of the changing trend of Fs caused by the tensile failure of rock bridges is solved by determining the tensile-shear composite failure mode. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A general sliding block model for calculating permanent displacement of slope is presented. Ground shaking can be applied to base or block in a direction horizontal or parallel to the inclined plane, with or without a simultaneous vertical component of ground motion, and the azimuth of the examined slope can be considered in the model. The effects of the application of excitation, the vertical component of ground motions, and the slope azimuth on earthquake-induced permanent displacements of near-fault seismic slopes are investigated using the model. The results indicate that: (1) The application of excitation has significant influence on the permanent displacements. (2) The influence of the vertical component of ground motion on the permanent displacement depends more on the phase synchronization of the horizontal and vertical components than on the amplitude. (3) The computed displacements are found to be very sensitive to the azimuth of the slope. [ABSTRACT FROM AUTHOR]

The purpose of this study is to investigate the stability of deep rectangular tunnels excavated in a jointed rock mass using adaptive finite element limit analysis (AFELA) method. The rock mass is assumed to obey the generalized Hoek–Brown failure criterion. The numerical results from parametric studies are presented in the form of dimensionless tables and figures concerning stability numbers (Ns). Typical failure mechanisms are depicted and discussed based on visualized results from AFELA. The results demonstrate that Ns decreases with geological strength index (GSI), increases with disturbance factor (D), stays nearly unchanged with the intact rock yield parameter (mi) and is less sensitive to GSI as D decreases. Besides, an analytical upper bound limit analysis method is also applied to provide a check on the validity of the results from AFELA. The influence of the excavation-induced disturbance on the stability of deep rectangle tunnels is investigated by introducing a disturbance coefficient (ζ). [ABSTRACT FROM AUTHOR]

Bedding slope is one of the most common forms of landslides, and determining the shear strength parameters of the sliding surface is essential for the slope stability analysis and engineering design. Due to the different values of shear strength parameters of different sliding surfaces and the existence of the interlayer shear effect during sliding, it is difficult to determine the shear strength parameters of the bedding slope with the multi-layer sliding surface, especially when the multi-layer sliding mass slides at different speeds at the same time. Therefore, the back analysis method combined with the upper-bound limit analysis method with reliability theory is proposed to back-analyze the shear strength parameters of the multi-layer sliding surface simultaneously. By analyzing three practical landslides in detail, the feasibility and applicability of the proposed method are validated. This method enables one to incorporate the effects of uncertainty and randomness of the parameters, and consider the interlayer shear effect, thus obtaining the most likely shear strength parameter combination and providing a reference for the strength parameter back analysis of bedding slopes based on the reliability theory. [ABSTRACT FROM AUTHOR]

Rainfall infiltration in unsaturated slopes alters the effective stress through pore water pressure changes, thus causing ground deformation. Although important to assess the timescale over which the margin of safety of a slope decreases, such coupled processes are rarely accounted in the context of spatially distributed hazard assessment procedures. In this paper, a physically based, spatially distributed model accounting for full hydro-mechanical coupling is discussed. The model relies on a vectorized finite element (FE) solver to calculate the stability of deformable unsaturated infinite slopes subjected to transient flow. First, the FE solver is used to study the response of individual slopes to a prolonged rainfall for three scenarios (i.e., rigid, swelling, and collapsible soil). Then, the model is used in the context of spatially distributed computations to assess spatiotemporal variations of factor of safety over a large area. For this purpose, a series of shallow landslides occurred in a mountainous landscape covered by collapsible loess deposits in northwestern China was used as test site. The analyses show that hydro-mechanical couplings affect the performance of the model in terms of computed failure time and areal extent of the unstable zones. Specifically, volume collapse due to suction decrease is found to reduce the time of failure compared with uncoupled computations obtained for a rigid soil scenario. The most substantial advantages of using coupled analyses have been reported with reference to gentle slopes, for which the higher rate of suction reduction driven by volume change was crucial to capture landslide source areas that would otherwise be overlooked by uncoupled analyses. The proposed methodology offers a complete tool for landslide hazard assessment, in that it incorporates sources of coupling between hydrology and mechanics that are crucial to replicate the physics of landslide initiation. [ABSTRACT FROM AUTHOR]

Grouting prevents groundwater leakage into tunnels, based on the exponent model that expresses the nonlinear variation of the hydraulic conductivity of the surrounding rock, the formulas for predicting the magnitude of water inflow and outer water pressure of the lining after grouting are deduced. The parameter analysis shows how the water inflow decreases as the hydraulic conductivity of the grouting circle diminishes and the thickness of the grouting circle increases. When the parameter α (attenuation coefficient), which expresses the decreasing amplitude of the permeability coefficient of the surrounding rock with depth, is greater than 0, the water inflow increases until it reaches a maximum at a certain depth, and then the inflow decreases to 0 if deep enough. After considering the variation in the hydraulic conductivity of the surrounding rock, the thickness and hydraulic conductivity of the grouting circle may be designed to be too large to reduce the magnitude of the water inflow. Meanwhile, to reach the limited drainage criterion of the tunnel groundwater, the grouting circle thickness decreases gradually as α increases after the nonlinear variation of the hydraulic conductivity of the surrounding rock, which can reduce the cost for plugging the groundwater. Thus, it is critical to consider hydraulic conductivity variation during water inflow predicting and grouting when designing tunnels. [ABSTRACT FROM AUTHOR]

Owing to the continuous rainfall, a bedding rockslide occurred at a construction site on the San-Li highway (Sandu County to Libo County) at 18:05 (UTC+8) on September 23, 2017, in Libo County, Guizhou Province, China. This bedding rockslide caused three deaths, six injuries, and an accumulation zone of approximately 1.8 × 105 m3 of medium weathered limestone that blocked the main line of the M ramp. To explore the triggering factors of this rockslide, the engineering geological condition, hydrogeological condition, slope excavation scheme, and statistics of rainfall data were investigated based on field investigations and geophysical drilling. The blasting failure of the upper unstable and dangerous rock masses after the bedding rockslide was analyzed. Three instability behaviors characteristics are distinguished: (1) the bedding characteristics of the rock formation and weak interlayer, (2) the steep slope (the largest dip angle being 46°), and (3) the appearance of the free face induced by the slope excavation. The results indicate that the above conditions are objective factors, and continuous rainfall triggers the bedding rockslide. The landslide follows the step-path failure mode. [ABSTRACT FROM AUTHOR]

The methods for calculating the elliptical cone's geometric parameters of multiple elliptical cone sliders were improved by introducing expression of elliptical path in 3D space. This elliptical path is the intersecting line of a cone and inclined cutting plane. Based on upper-bound limit analysis method and an improved method, Sequential Quadratic Programming (SQP) method was employed to obtain optimal upper bound solutions of failure pressure. The effectiveness of this method was verified by a comparative analysis, and a detailed parametric study on the failure pressure and failure modes was presented. In this study, the stability and failure modes of tunnel face are significantly affected by internal friction angle φ and dimensionless parameter C/D for both active and passive failure; by contrast, dimensionless parameters γD/c and σs/c have small effects. It is also found that dimensionless parameters C/D and σs/c have no effect on the results if the failure region does not reach the ground surface. [ABSTRACT FROM AUTHOR]

Due to the continuous and intense rainfall from June 26 to 28, 2016, Xinlu Village in Ganshui Town, Qijiang District, Chongqing, experienced a unitary-slip landslide at approximately UTC+8 19:30 on June 28. This landslide disrupted the Chuan-Qian railway and damaged four residential buildings. To analyze and rehabilitate the landslide, the engineering geology, hydrological conditions, and deformation instability mechanism of this landslide were investigated and comprehensively analyzed based on an in situ survey, geophysical drilling, and a laboratory quick-shearing test. The results show that the landslide is a typical gradual progressive landslide. [ABSTRACT FROM AUTHOR]

Based on a brief review of the existing shear strength reduction (SSR) techniques, the objective function of the comprehensive safety factor for simple homogeneous slopes is established by combining the double SSR technique (considered the shortest pathway of the strength reduction) with the upper bound limit analysis theorem, leading to a strict upper bound on the safety factor. Combining nonlinear sequential quadratic programming (SQP) with the random walk method, the value of the comprehensive safety factor can be optimized, avoiding the trap of a local minimum. Compared with classical examples, the present method is a conservative and effective method for slope stability evaluation. A set of design charts for homogeneous slopes under simple and typical conditions, such as surcharge load, pore water pressure, and seismic loading are produced by the analysis of substantial data, which can eliminate the necessity for iterations when calculating the safety factor. These stability charts are presented in a convenient manner to determine the comprehensive safety factors and corresponding failure patterns under different typical conditions, which might be preferred by engineers for performing the preliminary evaluations of slope safety. Several examples are used to illustrate the application of these stability charts under different conditions. [ABSTRACT FROM AUTHOR]

The stability of a plane strain tunnel face in a cohesive-frictional soil (idealized as a homogeneously Mohr-Coulomb material) subjected to ground surface surcharge loading was investigated. Continuous loading is applied to the ground surface, and both smooth and rough interface conditions are modeled. The upper-bound solutions with critical load parameters for a practical range of tunnel depth-to-height values, as well as the soil properties, are obtained by using the Upper-bound Finite Element Method with Rigid Translatory Moving Elements (UBFEM-RTME). For practical use, the results are presented in the form of dimensionless stability charts. Failure mechanisms consisting of two groups of slip lines, which explicitly reflect the relative movement of blocks, are also presented. To verify the solutions, the Upper-bound Finite Element Method with Plastic Deformation Elements (UMFEM-PDE) has been developed and the collapsed loads are compared with those from UBFEM-RTME. The solutions obtained with these two upper-bound finite element methods are found to be in good agreement with each other. [ABSTRACT FROM AUTHOR]

Timely and accurate mastery of the spatial and temporal development process of landslides is crucial for emergency rescue work. In the early morning of July 5, 2022, under the influence of continuous heavy rainfall, the left embankment slope of a highway in Guangdong Province, slipped as a whole, and a truck fell and was buried, resulting in the interruption of highway traffic. In order to accurately carry out landslide analysis and management, and to provide information support for emergency rescue and relief work, whole-process survey and analysis of the landslide area was carried out based on unmanned aerial vehicle tilt photography, 3D reconstruction and spatial analysis technology. In situations where traditional surveying and mapping work is difficult to carry out, it is possible to accurately grasp the whole process of the development of landslides in space and time under the circumstances and construct corresponding realistic three-dimensional models to provide effective reference information for on-site rescue and relief work. At the same time, through the comprehensive analysis of the acquired information, it is inferred that the landslide is a traction landslide under the effect of continuous rainfall. [ABSTRACT FROM AUTHOR]