SHAKING TABLE TESTS ON GRAVEL DRAINS TO PREVENT LIQUEFACTION OF SAND DEPOSITS

ABSTRACT Large scale shaking table tests were performed on the gravel drain system as a countermeasure to liquefaction of the sand deposits. The size of the shaking table is 12 m × 12 m and the size of models is 12 m in length, 3 m in depth and 2 m in width. The model sandy grounds with gravel drains and the half buried type road model were horizontally excited to investigate the effects of the gravel drains to prevent liquefaction of the sandy ground. Furthermore the cyclic laboratory soil tests and the finite element analyses were performed on the generation and dissipation of the pore water pressure during cyclic loadings. The following conclusions were obtained. i) The increase of the pore water pressure during the excitation becomes smaller near the gravel drain. The effective area of the gravel drain in this series of tests was less than 50 cm from the gravel drains. ii) The dissipation of the pore water pressure after the end of excitation can be accelerated by the gravel drain, iii) The large uplift acted on the half buried type road model by the pore water pressure generated during the excitation in the case that no countermeasure to liquefaction was installed in the model ground near the half buried type road model. On the other hand the uplift was remarkably reduced by installing gravel drains below the half buried type road model. The vertical gravel drains installed at both sides under the half buried type road model effectively functioned to stabilize the half buried type road model by preventing the water and sand flow from the outside area of the gravel drains. iv) The gravel drain system can be a good countermeasure to liquefaction of the sandy ground around the half buried or buried type structures, if it is appropriately designed. It is advantageous to use the gravel drains in such a way because the gravel drains with a filter zone can be easily installed around the half-buried and buried type structures since the ground is usually excavated before constructing such structures. v) The generation of the pore water pressure was calculated by using the two dimensional finite element computer program “SADAP” considering the dissipation of the pore water pressure. The calculation offered the relatively reasonable results on the pore water pressure buildup during the cyclic loading.