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The paper describes the recent devastating landslide of Kotrupi, Himachal Pradesh in India which had claimed many human lives and properties along its course on 13 August 2017. This event was the third reactivation of the slide as per data available. The study for this landslide involves a preliminary investigation of the site and comparison of pre- and post-event slope stability analysis. Other than rainfall, the combined effect of differential weathering rate of the debris and soil layers, low material strength, and the presence of a fault zone was found to be the primary cause of instability. The analysis was carried out with the geotechnical investigation and numerical modeling with the help of finite element model-based Phase 2 simulator. The significant findings of this paper include numerical simulation of pre- and post-event slide as stated under unsaturated and saturated condition. The study finds a low factor of safety of the present slope. The unstable condition of the slope may trigger another event of the same intensity shortly. [ABSTRACT FROM AUTHOR]

In slope stability analysis, identification of the mechanism behind slope failure is the key factor during the study. Rock mass characterization and kinematics analysis, like geotechnical investigation methods, are not infallible all the time for the weathered slopes. The presence of different grades of weathered mass on the slope profile acts independently to influence the overall failure pattern. Numerical analysis by finite element method (FEM) is evolved as a primary slope stability analysis tool by overcoming the limitations of the stratified weathered materials on the slope. The paper focuses on the stability analysis of railway-cut laterite slopes of the Eastern Ghats of India. The medium to high-grade metamorphism, followed by physio-chemical weathering, favours the region for more prone to failure. The Force Equilibrium Model and Moment Equilibrium Model have been considered to determine the possibility of independent failure events for the probability analysis. Monte Carlo's probability simulation method has delivered a better result for the weathered slopes by taking many variables for the studied region. A compression study has been made between the outcomes of slope stability analysis methods and the probability analysis models, which provides a comprehensive list of factors to understand the failure mechanism of weathered slopes. [ABSTRACT FROM AUTHOR]

Evaluation of stability of artificial slopes created due to road construction in the mountainous terrain is very important but often a neglected aspect. The safe execution of road-cut slopes depends upon the level of understanding achieved in defining the engineering behaviour of rock masses with respect to its deformation and mechanical attributes. Understanding the realistic response of the rock mass to excavation of rock strata requires proper analysis related to influence of structural elements on their continuous characterization for facilitating safe and economical development of cut slopes along the road sections. In this paper structurally and non-structurally controlled rock slope classification systems are implemented to undertake comprehensive evaluation of stability of road-cut slopes. The work carried out involves collection of various inputs in form of rock mass and discontinuity characteristics from ten cut slopes along a road section in Kullu area, Himachal Pradesh, India. Rock samples were collected from site and laboratory testing has been undertaken to determine the intact rocks strength. Beside these, the kinematic analysis was performed to illustrate the geometrical relationship between various joint sets and the slope face so as to determine their failure mechanism. Several rock mass classification systems developed for rock slope stability assessment are evaluated for known slope conditions. The stability assessment for all identified cut slopes is compared using slope mass rating (SMR), Q-slope and slope stability rating (SSR) methods. Design charts proposed for various factor of safety values have been utilized to evaluate the stability of studied road-cut slopes. Finally, a slope wise comparison is made between the stable angles predicted by SSR with those recommended by Q-slope method. [ABSTRACT FROM AUTHOR]

This article presents the challenges encountered during the stability analysis and stabilization of two Himalayan rock slopes supporting the Chenab Railway Bridge in India, which will be the highest railway bridge in the world after completion. Owing to the importance of the project, extensive geological investigations, in situ and laboratory tests were carried out using conventional and advanced methods to evaluate various intact rock, rock joints, rock mass properties and rock mass quality present at the site. Once the conclusive results were made regarding these properties, stability of slopes were evaluated against both structurally controlled and stress-controlled failures using the developed probabilistic approach due to the presence of high variability in intact rock, rock mass and rock joints properties. It was observed that while the slopes were stable against stress-controlled failures, the possibility of structurally controlled failures exists as observed in the probabilistic approach in which the conventional deterministic approach was not able to detect. Different stabilization measures, i.e. rock bolts, slope flattening, grouting, drainage and shotcreting, were designed at the site to reduce the probability of failures for the slopes, deformability of rocks present due to cavities and high aperture joints, shallow block failures along the slope surface and pore-pressure build-up. To check the efficiency of the stabilization measures, cross-hole seismic tomography is carried out at the site and further in situ measured displacements are compared with the displacements estimated using the developed probabilistic approach. The case study used in this paper is a real-time ongoing bridge project of global interest and the data and analysis presented will be of great benefit to the researchers and practitioners working on similar problems. [ABSTRACT FROM AUTHOR]

Probabilistic methods are the most efficient methods to account for different types of uncertainties encountered in the estimated rock properties required for the stability analysis of rock slopes and tunnels. These methods require estimation of various parameters of probability distributions like mean, standard deviation (SD) and distributions types of rock properties, which requires large amount of data from laboratory and field investigations. However, in rock mechanics, the data available on rock properties for a project are often limited since the extents of projects are usually large and the test data are minimal due to cost constraints. Due to the unavailability of adequate test data, parameters (mean and SD) of probability distributions of rock properties themselves contain uncertainties. Since traditional reliability analysis uses these uncertain parameters (mean and SD) of probability distributions of rock properties, they may give incorrect estimation of the reliability of rock slope stability. This paper presents a method to overcome this limitation of traditional reliability analysis and outlines a new approach of rock mass characterization for the cases with limited data. This approach uses Sobol's global sensitivity analysis and bootstrap method coupled with augmented radial basis function based response surface. This method is capable of handling the uncertainties in the parameters (mean and SD) of probability distributions of rock properties and can include their effect in the stability estimates of rock slopes. The proposed method is more practical and efficient, since it considers uncertainty in the statistical parameters of most commonly and easily available rock properties, i.e. uniaxial compressive strength and Geological Strength Index. Further, computational effort involved in the reliability analysis of rock slopes of large dimensions is comparatively smaller in this method. Present study also demonstrates this method through reliability analysis of a large rock slope of an open pit gold mine in Karnataka region of India. Results are compared with the results from traditional reliability analysis to highlight the advantages of the proposed method. It is observed that uncertainties in probability distribution type and its parameters (mean and SD) of rock properties have considerable effect on the estimated reliability index of the rock slope and hence traditional reliability methods based on the parameters of probability distributions estimated using limited data can make incorrect estimation of rock slope stability. Further, stability of the rock slope determined from proposed approach based on bootstrap method is represented by confidence interval of reliability index instead of a fixed value of reliability index as in traditional methods, providing more realistic estimates of rock slope stability. [ABSTRACT FROM AUTHOR]

The seismic slope stability analysis of the right abutment of a railway bridge proposed at about 350 m above the ground level, crossing a river and connecting two huge hillocks in the Himalayas, India, is presented in this paper. The rock slopes are composed of highly jointed rock mass and the joint spacing and orientation are varying at different locations. Seismic slope stability analysis of the slope under consideration is carried out using both pseudo-static approach and time response approach as the site is located in seismic zone V as per the earth quake zonation maps of India. Stability of the slope is studied numerically using program FLAC. The results obtained from the pseudo-static analysis are presented in the form of Factor of Safety (FOS) and the results obtained from the time response analysis of the slope are presented in terms of horizontal and vertical displacements along the slope. The results obtained from both the analyses confirmed the global stability of the slope as the FOS in case of pseudo-static analysis is above 1.0 and the displacements observed in case of time response analysis are within the permissible limits. This paper also presents the results obtained from the parametric analysis performed in the case of time response analysis in order to understand the effect of individual parameters on the overall stability of the slope. [ABSTRACT FROM AUTHOR]

Landslides may be caused either by natural process or human activity or combination of both. In many cases, modifications in hill slopes are carried out with or without proper slope stability analysis, even though the consequences are well known. In other cases, stable slopes are converted into unstable slopes by the people residing in the area by artificial modification/alterations of the hill slope without basic knowledge of hill slope management. Such cases are very common in the hilly terrain including northeast India and they have caused loss of many lives even though the size of such landslide are very small. The present paper describes four examples from different parts of the northeast India where the terraced hill slopes that remained stable for an appreciable length of time have been converted to unstable slopes. [ABSTRACT FROM AUTHOR]