冻土三轴蠕变特性试验研究及平面冻土墙厚度的确定

Experimental study of triaxial creep properties of frozen soil and thickness determination of flat frozen soil wall

主要是对冻土的三轴蠕变特性进行分析研究,从而进一步确定具有明显流变特性的平面冻土墙的厚度。通过对冻土的流变特性进行理论分析,建立了冻黏土在复杂应力状态下的对数型蠕变方程。采用"低温箱-三轴压力室"轻型试验设备系统对人工配制的冻黏土试件进行了三轴蠕变试验,获得了冻黏土在复杂应力状态下的蠕变曲线。根据试验结果,对冻黏土的对数型非线性蠕变方程进行回归分析,得到了冻黏土对数型蠕变方程参数的数值。根据冻土流变理论和所建立的蠕变方程,以及平面冻土墙的厚度计算公式,利用Visualc++6.0和Matlab 6.0技术开发了冻土墙厚度计算的计算机应用软件。分析研究了平面冻土墙厚度与跨度、基坑暴露时间、基坑开挖深度的关系。平面冻土墙厚度随时间的延长在短期内具有急速增长的趋势,而后随时间的延长逐渐趋于稳定;平面冻土墙厚度受其跨度的影响较小,但随基坑开挖深度的加深具有逐步增长的趋势;温度对平面冻土墙厚度的影响显著,温度越高,厚度越大,所以,控制温度是平面冻土墙设计中的关键。从而为蠕变变形较大的平面冻土墙的厚度确定提供了依据。

In order to determine the thickness of flat frozen soil wall with evident rheological properties, the triaxial creep properties of frozen soil are analyzed. Through theoretical analysis of rheological properties of frozen soil, the logarithmic creep equation of frozen clay is established under complex stress state. The triaxial creep tests for manual prepared frozen clay specimens are carried out by ＂cold box-triaxial pressure chamber＂ light test equipment system; so that the creep curves of frozen clay under complex stress state are obtained. According to the test results, the logarithmic creep equation parameters of frozen clay are obtained through regression analysis of logarithmical nonlinear creep equation. According to the theological theory of frozen soil and the established creep equation, as well as the thickness formula of fiat frozen soil wall, through adopting Visualc＋＋ 6.0 and Matlab 6.0, the computer application software is exploited which can calculate thickness of frozen clay wall. With the softnvare, the relationships between the thickness and the span, the pit exposure time, and the pit excavation depth are analyzed. The thickness of flat frozen soil wall possesses rapid growth trend with time extension in the short term and then gradually becomes stable. The thickness of flat frozen soil wall is affected lightly by the span; but it possesses gradual upward trend with the increasing of excavation depth of pit. The temperature affects the thickness of flat frozen soil wall significantly; the higher the temperature is, the larger the thickness is. Consequently, controlling the temperature is the key to the design of flat frozen soil wall. Thus, the results provide a basis for thickness determination of fiat frozen soil wall with a large creep deformation.