Soil Type Based Mitigation Charts of Chure Landslides in Finite Element Framework

Abstract

Chure area is extended as a contiguous landscape from east to west in thirty-six districts in Nepal which is bordered by the Mahabharat range in the north and by the Terai in the south. There are more than five thousands of landslides in the chure area and there is no any methodology for mitigation and conservation of Chure area. There is no possible to go for site and case specific analysis and design of all those landslides. Therefore to find the general mitigation solution a general mitigation model is prepared to suit the chure landslide and prepared a set of mitigation Charts. This research works out on Site specific analysis and general mitigation analysis in parallel way. Three major landslides are taken for the site specific analysis. FEM based open source commercial software Phase2 is used for the stability analysis with mitigation measure. The charts developed are from the eight type of soil found in chure area for the plain strain or 2D conditions without considering any seismic loads. Five different slope angles (30ᵒ, 35ᵒ, 40ᵒ, 45ᵒ, 50ᵒ) have been considered which is either completely dry, saturated or GWT some depth below. The vegetation is applied to soil having ERD 1m and ERD 2m with increase in root cohesion upto 20 KN/m2 and friction angle by 5 degree. The retaining wall is applied at the toe of landslide with variation in height (h/H ratio 0.2, 0.3 and 0.4).The slope modification is done with equal cut and fill approach to the original slope angle. From the analysis of Charts, the effect of mitigation measures seems well significant when the slope is more than 45 degree and water table is more than 4m down from the surface level. Furthermore we found that maximum increase in FOS value is obtained with the application of slope modification mitigation measure and minimum increase in FOS value is obtained with the application of Retaining wall. The verification of FOS value obtained from the FEM based model is compared with the FOS value obtain from LEM based another tool Slide6 and satisfactory result is obtained with good correlation.