6.5.2 Density of mesh

In principle，the mesh in the area of stress concentration，of rapid strain changing，the crucial areas，and the object zones should be finer.The retaining wall is a rigid structure and soil is comparatively a soft material.The mesh in the transition zone between the wall and the surrounding soils should，therefore，be as fine as possible，since a larger stress gradient will be generated there.The farther from the wall，the lower the density of mesh can be.

Since the unloading forces caused by excavation act directly on the excavation bottom in the excavation zone，the density of mesh in the excavation zone will greatly affect the analysis results.Thus，the density of mesh in the excavation zone should be as fine as possible，as shown in Figure 6.14（Ou et al.，1996）.

Figure 6.14 The finite element meshes used in the analysis of excavation