高铁堑坡粉质黏土原位强度特性与应力历史效应

针对高速铁路堑坡防护工程不同施工工序中坡体强度参数选取问题,基于原位孔内剪切试验,依托哈佳高速铁路工程,通过成孔后施加不同法向应力水平的固结剪切和先施加较高法向应力(这里称为预加荷载pr)后卸载至某一应力水平再固结剪切等工况下的现场试验,获取堑坡粉质黏土强度特性随荷载施加方式的演化规律.结果表明:粉质黏土原位应力-位移曲线总体上呈弱硬化变形特征;应力历史对粉质黏土的抗剪强度影响显著,主要体现在黏聚力上,预加荷载由0 kPa增加到400 kPa时,土体黏聚力显著增加,增幅在18.7～51.8kPa之间;内摩擦角降幅甚微.粉质黏土的黏聚力和施加预加荷载后的黏聚力增量均与含水率呈线性负相关,但随着含水率的增加,支护荷载存在临界值.黏聚力与预加荷载呈线性正相关,在实际工程中,可根据工程要求达到的安全系数,通过黏聚力和预加荷载的关系反推出所需预加荷载大小,从而为实际工程设计与施工提供借鉴参考.

In-situ Strength Characteristics and Stress History Effect of Silty Soil on High-speed Railway Cut Slope

Considering the issue of reasonably selecting the strength index in different construction procedures of high-speed railway cut slope, borehole shear test (BST) was carried out on silty soil. The influence of loading addition way on in situ strength characteristics of silty soil was studied by adding different normal stress levels and unloading to a certain stress after adding a higher normal stress (herein called preloading), taking Hajia high speed railway as engineering background. The results show that in-situ stress-strain curves of silty soil generally present the variation characteristic of weak hardening. Preloading greatly contributes to the shear strength, mainly in cohesion. With the increase of preloading from 0 kPa to 400 kPa, cohesion increases distinctly in the increment of 18.7~51.8 kPa, while internal friction angle rarely varies. Both cohesion and its increment after the preloading are nearly negatively linear to the water content of silty soil, but a critical preloading may occur when water content reaches to a certain value. The cohesion is positively linear to preloading, which should be fully used to back calculate the required preloading according to the safety factor that the project should satisfy. It provides a reference to engineering design and construction.