Sand drains have been widely used as one of the most popular soil improvement method. In the Japanese highway construction, test embankments are frequently constructed to investigate the effectiveness of sand drains.
In almost all the test enbankments, sand drains were not effective in accelerating settlement.
　The conventinal consolidation theory fails to simulate the case histories where sand drains were not effective. THis is due to fact that it assumes unrealistic
conditions; one dimensional deformation with an elastic mechanical model for soil.
　In order to reproduce real conditions in the field, two dimensional consolidation analysis was carried out by the finite element method using elasto - viscoplastic model for clay. It is shown that the finite elements can simulate observed settlement of many case histories. According to the finite element analysis, sand
drains seem to have small effect on accelerating settlement.