冻压条件下冻融软土孔隙特征与动力特性分析

Experimental study on pore features and dynamic behaviors of soft clay under different confine pressures during freezing

杭州软土地区地铁联络通道建设多采用冻结法施工,在整个冻结范围内,不同区域的土体冻融期间承受不同冻结温度与冻融压力。通过自主研发土样制作仪器,得到不同组合冻结条件的试样,再基于核磁共振试验,研究冻融土在不同冻结压力、冻结温度以及加载情况下精确孔径分布特征曲线变化规律,并结合动三轴试验深入探究以孔压、应变以及刚度为代表的动力特性。最终,建立以一次对数为基础的动孔压预测模型,该模型参数物理意义清晰,能较好地预测不同冻融条件下软土动孔压发展。研究结果表明:随着冻结温度的降低,孔隙中的水冻胀效果更为明显;冻融期间围压可有效使融土骨架结构更为紧密,从而减少融土在循环荷载下的变形;循环荷载作用下,小孔隙尺寸大幅度减小,尺寸分布范围增大,中等孔隙进一步向次级孔隙发展;不同冻融压力作用下,孔压极限值与冻融完成后中等孔隙的面积呈类线性相关。研究成果可作为冻结法施工条件下,预测冻融土结构损伤程度与循环荷载下孔压发展的可靠依据。

The construction of subway connection channels in Hangzhou is mostly carried out by freezing method,which leads to uneven settlement during operation. In the whole range of frozen soil,the freezing conditions change with the relative relationship between the soil and the freezing pipe. Soil samples frozen under different freezing conditions were obtained using sample making instrument invented by the authors. Nuclear magnetic resonance(NMR) tests were performed to study the variation of pore size distribution curve of freezing-thawing soil under different freezing conditions, and the pore pressure,strain and stiffness of the samples were deeply explored combined with dynamic triaxial test. A concise pore pressure prediction model of soft clay under artificial freezing with clear physical parameters was established. The results show that, with decreasing the freezing temperature,frost-heaving brings about worse destruction of the soil structure. During freezing-thawing period,the confining pressure can effectively compact the framework structure of the soil and reduce the deformation under cyclic loads. The limit value of the pore pressure is linearly correlated with the area of medium pores of pore size distribution curve.