初始静孔隙水压力对砂土静动力剪切特性影响的试验研究

选取福建标准砂和滹沱河细砂,利用空心圆柱扭剪仪开展了一系列不同初始静孔隙水压力条件下的不排水循环扭剪试验和单调扭剪试验,着重探讨初始静孔隙水压力对超静孔隙水压力发展及其不排水抗剪强度的影响。试验结果表明:初始静孔隙水压力对超静孔隙水压力的发展产生显著的影响,从而影响砂土的静动力剪切特性。具体地,在不排水循环剪切过程中,初始静孔隙水压力越大,其超静孔隙水压力发展和变形发展越快;在不排水单调剪切过程中,初始静孔隙水压力越大,在砂土剪胀阶段产生负超静孔隙水压力越大,从而使砂土的强度显著提高。基于试验结果,初步探讨了初始静孔隙水压力对超静孔隙水压力及静动力剪切特性的影响机理。研究表明,研究地下水位以下土体(准饱和土)静动力剪切特性尤其是研究液化问题时,应充分考虑初始静孔隙水压力对砂土抗液化强度的影响,室内试验应根据砂土所处的地下水位深度来决定初始静孔隙水压力(反压)的大小。

Experimental study on effect of initial static pore water pressure on static and dynamic shear properties of sand

A series of undrained cyclic torsional shear tests and monotonic torsional shear tests are carried out on Fujian standard sand and Hutuo River fine sand under different initial static pore water pressures by using the hollow cylinder torsional shear apparatus in order to emphatically discuss the effects of the initial static pore water pressure on the development of the excess pore water pressure and undrained shear strength. The experimental results show that the initial static pore water pressure has a significant effect on the development of the excess pore water pressure, which affects the static and dynamic shear characteristics of sand. Specifically, during the undrained cyclic shear process, the greater initial static pore water pressure leads to the faster development of the excess pore water pressure and deformation. During the undrained monotonic shearing process, the greater the initial static pore water pressure, the greater the negative excess pore water pressure during the sand dilatancy, which significantly increases the strength of the sand. Based on the test results, the mechanism of the influences of the initial static pore water pressure on the excess pore water pressure and static and dynamic shear characteristics is preliminarily discussed. According to the results, the influences of the initial static pore water pressure on the anti-liquefaction strength of sand should be fully considered when we investigate the static and dynamic shear characteristics of soil (partially saturated soil) below the groundwater table, especially the liquefaction problem. In laboratory tests, the initial static pore water pressure (back pressure) should be determined according to the depth of underground water level where the sand is located.