The combination of these results were used for calculating the factor of safety (FoS) by Limit Equilibrium Method (LEM) proposed by Bishop and Janbu methods. These soil parameters indicate the soil is very low strength. Geotechnical analysis such as grain size analysis, liquid limit and direct shear test were carried out in order to evaluate soil classification, moisture content, cohesion and the angle of internal friction of soil for knowing the strength the soil. The geophysical survey (Electrical Resistivity Tomography-ERT) were carried out to know the electrical resistivity of soil for identifying the groundwater table and hence slip surface of the landslide. Geological study was carried out by detail mapping of surface geology, soil condition, properties of bedrock and its discontinuities. ĭetailed investigation of Taprang landslide was carried out in order to understand the surface, subsurface lithological information and physical properties of soil by using multi-disciplinary methods such as engineering geological, geophysical and geotechnical studies for the determination of factor of safety for slope stability analysis. Similarly the results from Rocscience Slide-6.0 are conforming to FEM. drawdown case, the critical strength reduction factor is equal to unity indicating a possible chance of slope failure as was the case in actual. full capacity reservoir is 2.7 suggesting a stable slope. The critical strength reduction factor for case 1 i.e. This section includes the results of stability analysis from FEM and Limit equilibrium approach. The analysis results are shown in Figure 5.
Analysis in Rocscience Slide-6.0 focus only on rapid drawdown case as this is the more critical scenario when sudden removal of water can reduce the stability on the upstream slope of reservoir and hence the cyclic loading condition can be simulated in this manner as there is insufficient time for the pore water pressures to stabilize and maintain equilibrium state. Auto- refine slope search option was used to determine the minimum factor of safety for most critical slip surface. Circular slip surface was defined and slope limits were so adjusted that the critical slip surface passes through the points as shown in Fig.
technique, for maintaining the mass in equilibrium, depending on the three basic equations of equilibrium.
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