INTERNAL BEHAVIOR OF CLAYEY GROUND IMPROVED BY VERTICAL DRAINS IN 3D-CONSOLIDATION PROCESS

In order to establish a precise method for predicting the residual settlement, including the secondary consolidation, of clayey ground improved by vertical drains, a new consolidation test apparatus was developed. In this test apparatus, the consolidation of a hollow cylindrical body, in which the pore water flows radially toward the center, can be simulated by installing a vertical drain at the center of the specimen. The radial distributions of the radial displacement and excess pore water pressure in the specimen during the three-dimensional consolidation process also can be measured in this test apparatus. The radial displacements in the specimen were obtained by measuring the intensity of the magnetic field induced by a small magnet buried in the specimen by magnetometers set in the consolidation ring surrounding the specimen and in the vertical drain installed at the center of the specimen. From the measured results on the radial displacements in the specimen, it was found that during the three-dimensional consolidation process not only the vertical displacement but also the radial displacement occurs inside the specimen. The radial displacement developed toward the center of the specimen in the early stage of consolidation and then returned toward the outside in the later stage of consolidation but did not completely return to the original position at the end of consolidation. The mechanism of the three-dimensional consolidation by the vertical drain, which caused these behaviors, was clarified based on the test results on the radial distributions in the radial displacement and the excess pore water pressure in the specimen.