基于动强度试验确定饱和砂土弱化参数的方法

An Approach for Determining the Weakening Parameters of Saturated Sand based on Dynamic Strength Test

对于可液化土层,若土体发生液化则认为土体强度完全丧失;而对于没有发生液化的土层,一般不考虑超孔隙水压力对土体强度的影响。实际情况下,具有超孔隙水压力的饱和砂土在地震荷载作用下强度会发生弱化,以往对于可液化土层中桩土相互作用问题的研究都是针对土体完全液化的情况展开的,忽略了液化过程中超孔隙水压力对其强度的影响。通过竖向-扭转双向耦合剪切仪对福建标准砂进行循环扭剪动强度试验,结合MohrCoulomb强度理论,计算得到不同孔压比下饱和砂土的弱化参数,并根据有效应力原理建立了弱化状态下土体弱化参数与孔压比之间的数学关系。结果表明:液化过程中超孔隙水压力对土体强度弱化的影响可以用土体弱化参数来表示;孔压比越大,土体强度弱化越严重,相应的弱化参数也越小,反之则越大。

For a liquefiable soil layer,the strength of soil is considered to be lost completely if the soil is liquefied;And for the soil without liquefaction,the influences of the excess pore water pressure on the soil strength are generally not considered.In practice,the strength of saturated sand with excess pore water pressure will be weakened by the action of seismic load.Most previous studies on pile-soil interaction in liquefiable soil were carried out on completely liquefied soil,and the influences of excess pore water pressure on soil strength were neglected during the development of liquefaction.In this paper,cyclic torsional shear strength tests are carried out on Fujian standard sand by employing the vertical-torsional coupling shear apparatus.The weakening parameters of the saturated sand at different pore water pressure ratios are calculated by combining with the Mohr-Coulomb strength theory.The mathematical relationships between the weakening parameters and pore water pressure ratios in different weakening states are established according to the principle of effective stress,which will provide important references for further calculation of pile-soil interaction and pile foundation design.Result shows that the influences of excess pore water pressure on weakening of soil strength during liquefaction can be expressed by soil weakening parameters;With the increase of pore pressure ratio,the weakening of soil strength will be more serious,and the corresponding weakening parameters will be smaller,and the vice versa.