北疆某工程膨胀土的力学特性及微观机制试验研究

北疆某工程穿越膨胀土区域，自运行以来发生多次滑动破坏，为深入探讨其破坏机理，通过对膨胀土进行室内直剪、压缩、渗透及扫描电镜试验，从宏观角度分析其力学特性，微观上揭示其物理机制。宏观分析表明：随含水率增加，黏聚力降低，内摩擦角呈先增后减趋势，在最优含水率时达到峰值；随干密度增加，黏聚力增加，内摩擦角呈逐步增大的趋势；随含水率增加，稳定孔隙比呈下降趋势，表明土体的压缩性增强；随干密度增加，初始孔隙比减小，稳定孔隙比趋于定值。电镜扫描结果显示：随固结压力增加，土体的结构类型由絮凝结构逐渐向紊流和层流状结构演化，孔隙数量与大小均下降，颗粒聚集效应明显，膨胀土压缩性降低；膨胀土在低固结压力下渗透性较强，在较高压力（200～1 600 kPa）下较小，渗透系数量级为10-6～10-8，与孔隙比呈正相关，可用幂函数的形式表达；随固结压力增加，松散堆积结构转变为紧密结合的层流状结构，孔隙面积减少，渗透系数显著降低。

Experimental study on mechanical properties and microscopic mechanism of expansive soil in a project in north Xinjiang

A project of north Xinjiang has encountered multiple sliding failures since running which across expansive soil area. Our primary aim is to explore the sliding failure mechanism. Therefore, the indoor direct shear test, compression test, seepage test and electron microscope scanning test of soil are carried out separately, the results of mechanical properties of soil are investigated and their affecting mechanism is discussed. The cohesion decreases with the increase of water content. The internal friction angle decreases slowly when it is less than the optimal water content, and then decreases significantly. Due to dry density increasing, the cohesion increases significantly and the internal friction angle increases more slowly. According to the analysis result, the stable void ratio decreases with increasing water content, and the compressibility of soil increases. With increasing dry density, the initial void ratio decreases, and the stable void ratio tends to be constant. With increasing consolidation pressure, the structure type of soil gradually evolves from flocculation structure to turbulence and laminar flow structure, the effect of particle aggregation is obvious, the number and size of pores decrease, and the compressibility of expansive soil decreases. All the above results are obtained based on the result of scanning electron microscopy experimental test (SEM). The permeability of expansive soil is strong under low consolidation pressure, and it is small under high pressure (200~1 600 kPa), with an order of 10?6~10?8. The permeability coefficient is positively correlated with the void ratio, which can be expressed in the form of power function. The results of scanning electron microscopy (SEM) show that the loose accumulation structure changes into a closely combined laminar flow structure with increasing consolidation pressure, and the area of pores decreases, which provides the conditions for the permeability coefficient to decrease significantly.