Dissipation of pore water pressure in soft foundation reinforced by vacuum drainage preloading

The strength of soil can be improved by dissipating the pore water pressure by means of vacuum drainage preloading.In this paper,the in-situ experimental data of a bridge pier foundation is used to analyze the dissipation law of pore water pressure in silt and sand in the process of preloading.The result shows that the dissipation of pore pressure consists of two parts.One is formed by the direct effect of vacuum and the other is due to the lowering of groundwater table.The dissipation of pore water pressure in silt is resulted from lowering of the groundwater table,while in sand well and in the vicinity of plastic drainage plate it is resulted from the effect of vacuum.The degree of dissipation does not change along the depth but the effect of dissipation will be maintained even in the depth of 4～5m below the plastic drainage plate.Consequently,the plastic drainage plate is the best way for reinforcement of foundation.