冲击荷载下层状饱和无粘性土动孔压发展模式研究

Study on the Development Mode of Dynamic Pore Pressure in Layered Saturated Non-Cohesive Soil Under Impact Loading

为揭示饱和无黏性土层在冲击荷载作用下动孔压发展模式及其受土层条件的影响,基于自主研制的冲击荷载加载台装置,开展了不同土层条件层状饱和土冲击试验,对动孔压发展特征及土体沉降等进行了分析。结果表明:冲击荷载作用下,无粘性饱和土体动孔压发展呈明显两阶段,即瞬态响应和稳态响应阶段,其中稳态响应阶段动孔压发展又经历缓慢下降及快速下降两过程。单层土情形下,饱和砂土在冲击荷载后动孔压发生骤增,随着粒径的增大,动孔压峰值越大,但其消散用时则随粒径的增大而减小;双层土情形下,动孔压稳态响应阶段因上下土层渗透系数变化,在其下层土动孔压下降过程产生明显变化;当含有相对弱透水夹层时,受弱透水层影响,各测点动孔压下降段几乎在同一时刻均出现明显转折平台,使其下降的速率明显变小,且该现象弱透水层以上土体较其下部土体更为显著;含夹层时,试验过程出现明显非均匀分布的“水膜”,最大厚度可达2 cm左右。同时,每次冲击荷载下均伴随明显的土体沉降,随着冲击次数增加,土层沉降变化量逐渐减小。

This study aims to uncover the development modes of dynamic pore pressure in saturated non-cohesive soil layers under impact loading and its variation due to soil layer conditions.Impact tests were conducted on layered saturated soil under different soil layer conditions using a self-developed im-pact load testing device,and the characteristics of dynamic pore pressure development and soil settle-ment were analyzed.The results showed that under impact loading,the development of dynamic pore pressure in soil underwent two distinct stages:a transient response stage and a steady-state response stage,with the latter characterized by a slow followed by a rapid decline.In single-layer soil,the dy-namic pore pressure in saturated sand soil increased sharply after impact loading.With the increase of particle size,the peak pressure rose and the dissipation time shortened.In dual-layer soil,the steady-state dynamic pore pressure stage changed significantly due to permeability coefficient variations be-tween the upper and lower soil layers,markedly altering the reduction process in the lower soil layer.Presence of a relatively impermeable interlayer caused a noticeable plateau across all measuring points in the pressure reduction phase,significantly slowing the decrease rate,particularly in the soil above the impermeable layer compared to below it.With interlayers,experiments showed significant"water film"formation with non-uniform distribution,reaching up to 2cm in thickness.At the same time,each impact load resulted in noticeable soil settlement,and the extent of settlement gradually dimin-ished with subsequent impacts.