马汊河膨胀土特性室内试验研究及数值计算分析

Laboratory Test and Study and Numerical Calculation and Analysis for Characteristics of Expansive Soil at Macha River

膨胀土是导致边坡失稳的不利因素之一,对其进行特性研究是十分必要的。通过室内物理参数试验以及原状土干湿循环试验,分析膨胀土自由膨胀率、含水率等基本物理性质随土层深度的变化规律,研究其裂隙变化及强度变化规律,并建立数值计算模型,进行堤防迎水坡坡比、堤防高度及宽度对其安全稳定的敏感性计算分析。研究表明,马汊河膨胀土含水率大部分集中在20%左右,土体处于硬塑态;膨胀性土层分布与地质土层分布不一致,有呈沿坡面等深分布现象;随着干湿循环次数的增加,约在4次干湿循环后,试样开始出现大的裂隙且逐渐形成网状至破坏;其黏聚力c及内摩擦角φ值也在干湿循环过程中不断减小,经历8次干湿循环后,膨胀土的强度参数基本趋于稳定;膨胀土边坡安全系数与迎水坡坡比及堤防宽度成正比,与堤防高度成反比;且在经过4或5次干湿循环试验后,其安全系数下降速度最快,下降量约占初始安全系数数值的83%,为膨胀土地区边坡设计提供参考依据。

Expansive soil is one of the unfavorable factors leading to slope instability,so it is essential to study its characteristics.This paper analyzes the variation rules of basic physical properties such as free expansion rate and water content with soil depth and studies the variation rules of crack and strength of expansive soil through physical parameter test at laboratory and wetting-drying test of undisturbed soil,as well as calculates and analyzes the sensitivity of upstream slope ratio,height and width of embankment on its safety and stability based on a numerical calculation model.The results show that:the moisture content of expansive soil at Macha River is mainly about 20%,and the soil is in hard plastic state;with isobathic distribution along the slope,the distribution of expansive soil layer is inconsistent with that of geological soil layer;with the increase of the number of wetting-drying cycles,the large cracks appear on the sample and gradually form a network for damage after about 4 wetting-drying cycles;its cohesion c and internal friction angleφalso decreased in the process of wetting-drying cycles,and the strength parameters of expansive soil basically become stabilize after 8 wetting-drying cycles;the safety factor of expansive soil slope is in direct proportion to the upstream slope ratio and embankment width and in inverse proportion to embankment height;after 4 or 5 wetting-drying tests,its safety factor decreases at the fastest speed,with drop-out value accounting for about 83%of the initial safety factor,which provide reference for slope design in expansive soil area.