Variation law of pore water pressure in soil improved by underwater vacuum preloading method

Abstract

The measurement and analysis of pore water pressure is significant for the studies on under water vacuum preloading method. In order to study the variation of pore water pressure, the full-scale field tests were performed. It was indicated that the variation of pore water pressure was influenced by water pressures on the sealing membrane and negative pressures in sand cushion. The variation of stress in soil was equal to the difference between the values of pore pressure before and during vacuum preloading, indicating that water pressures on the sealing membrane could act as preloading loads. When the depth of water on membrane increased, the positive pore pressure would be induced in soil which, and it similar to the surcharge load. The distribution of negative pore pressure in soil was not uniform, causing differential settlement and strength increase.

孔隙水壓力的量測和分析對研究水下真空預壓法具有重要意義。在已經完成的水下真空預壓現場試驗中,把孔隙水壓力做為主要研究對象進行了監測。結果顯示孔隙水壓力的變化受膜上水壓和膜下負壓的影響。水下真空預壓期間土體中各點應力的改變等于加固前孔壓與加固過程中孔壓之差。膜上水壓可以做為預壓荷載。當膜上水壓增大時,增加的水壓使土體產生正的超靜孔隙水壓力,相當于堆載。水下真空預壓過程中負超靜孔壓分布的不均勻使加固區內產生差異沉降和不均勻的強度增長。