细粒土与粗粒土动力流化的孔压差异辨析

Analysis of Pore Pressure Difference Between Fine-and Coarse-grained Soils During Dynamic Fluidization

地基土体在动力作用下的液化对工程会产生灾害性影响。孔隙水压力是研究饱和土体转变为流体的重要表征,已有研究发现,细粒土在液化过程中即使孔压比(孔压/围压)未达到1,也已进入液化状态。本文将土颗粒概化为球体,考虑颗粒吸附水膜的影响,对由砂粒、粉粒、黏粒组成的饱和土体,在可发生流动的情况下,建立产生动力流化的理论模型,并分析了动三轴和振动台实验中孔压的变化。结合土体微结构特征,指出细粒土处于流化状态时,孔隙水压力因受结合水膜影响而导致孔压值减小,同时因颗粒形状(如板片等)的框架支撑作用也可减小孔压值。这一从土体微观组成的物理性质上进行的理论分析,有助于厘清以孔隙水压力判别细粒土与粗粒土发生动力流化标准不同的原因,有助于研究者深入理解土体液化的内在机制。

Liquefaction of foundation soils under the action of dynamicforces can have disastrous effects on the engineering.Pore water pressure is an important parameter for saturated soil transforming into fluid.The exsiting studies have found that during the process of liquefaction,fine-grained soil can enter the liquefaction state even if the pore pressure ratio(pore pressure/enclosure pressure)does not reach to 1.A theoretical model for generating dynamical fluidization in the cases where a flow can occur is established for saturated soils composed of sand,silt and clay particles.In the model,the soil particles are assumed to be spheroids and the influences of particles adsorbing water film are taken into account.In addition,the changes of pore pressure in dynamic triaxial and shaking table experiments are also analyzed.Based on the characteristics of soil microstructures,it is proposed that when fine-grained soil is in a fluidized state,the pressure of pore water can cause the pore pressure to decrease due to the influence of bound water film.Mesnwhile,the pore pressure can also be reduced due to the framework support of particle shapes(e.g.the plate shape).This theoretical analysis conducted according to the physical properties of the soil microscopic compositions can help to clarify the reasons for the difference in dynamic fluidization criteria between the fine-grained soil and the coarse-grained soil based on pore water pressure and to understand further the intrinsic mechanism of the soil liquefaction.