Finite difference analysis of anchored earth retaining structure

Abstract

Due to the development of materials and enhancement in technical understanding of geotechnical engineering, different types of soil retention systems have evolved over the last three to four decades. These systems may be classified into two groups; externally stabilized walls and internally stabilized walls. The internally stabilized walls comprise of horizontally laid reinforcements which carry most or all of the lateral earth pressure via soil-reinforcement interaction or via passive resistance from the anchor block. In this thesis analysis of an anchored earth retaining wall is undertaken using a threedimensional explicit finite difference program. To generate the model Mohr-Coulomb constitutive model is used in this study. The parameters studied are (1) vertical cable spacing (2) fill soil property (3) cable diameter and (4) horizontal cable spacing. Emphasis is placed to investigate the variation of (I) mid section deflection of the wall and (2) stress in the cable at different levels with the above mentioned parameters. A 6.6m high vertically faced anchored earth wall is modeled by using a finite difference program called FLAC3D. The wall is comprised of alluvial sandy soil as reinforced soil (Poisson's ratio 0.15), reinforcement and retained soil (same as reinforced soil). No facing element and anchor plate is used for simplicity ofthe model. From the analysis it can be concluded that deflection of the wall front decreases with a decrease in the vertical cable spacing and near the base of the wall deformation is zero. On the other hand stress in the cable decreases with a decrease in the cable spacing due to smaller contributing area to a cable strip and maximum stress occur at about 60 percent length of the cable from the wall. Variation of shear strength of soil reveals that as the shear strength is increased deflection of wall front as well as the stress of the cable decreases. The parametric study of horizontal spacing of cable ended with the findings that wall front deflection and cable stress increases with the increase of horizontal spacing. It can also be said that cable stresses increases and deflection of the wall front decreases with the increase of cable diameter. Finally it can be concluded from above study that Finite Difference method may successfully simulate the behavior of anchored earth system.