A thesis submitted in partial fulfilment of the requirements for the degree of Master of Engineering, School of Engineering and Technology

Thesis (M.Eng.) - Asian Institute of Technology, 1979

In order to study the characteristics of the foundation soil disturbed by the installation of displacement type sand drains a series of sand drain model tests were performed in the laboratory by means of the Modified Rowe Consolidation cell apparatus Undisturbed samples were taken from depths 2.50 m to 8.0 m from the ground surface with a sample spacing of 0.75 m. Model tests with four drain columns, 1.0 cm. in diameter were performed using cylindrical specimens of 6.0 in.in diameter and 1.5 in. thick. Also four drain columns, 1.5 cm. in diameter were installed in other specimens. These drain columns were installed by means of a driven mini-mandrel and the hole was filled with saturated sand. The standard consolidation tests were performed on the undisturbed samples. The direct shear tests were also performed on consolidated specimens with sand drain columns. It was found that the time required for the 100% primary consolidation of the specimen with sand drain columns evaluated from the compression-time relationships was longer than the time for the 100% primary consolidation of the specimen without sand drain columns. The increase in diameter of sand columns from 1.0 cm. to 1.5 cm. increases the undrained shear strength of the speciment. The increase in diameter of sand columns from 1.0 cm to 1.5 cm decreases the radial coefficient of consolidation. The total settlement of the specimen with sand drain columns is higher than the total settlement of the specimen without sand drain columns. The influence of sand drains installed by driving a closed and mandrel on the rate of consolidation, the undrained shear strength, the radial coefficient of consolidation of the soft foundation soil should be considered in the design method.