饱和软黏土固结过程中的不排水抗剪强度特性

集成大直径固结仪和微型十字板剪切仪的功能,开发和研制了饱和软黏土固结过程中可以随时开展剪切试验的系统装置,考虑超孔压随时间和空间变化的不均匀性,在微型十字板剪切仪板头处的空心轴杆底端配置微型孔压计,并在大直径固结仪中配置微型土压力计,使其具备自动实时监测在十字板剪切试验测点处有效应力变化的功能。利用该系统装置,开展了饱和软黏土在不同固结压力作用下,固结过程中不同时点的十字板剪切试验,实时监测了固结过程中的变形和孔压变化过程,得到了十字板剪切试验测点处的有效应力和不排水抗剪强度,分析了固结过程中不排水抗剪强度和有效应力之间的相关关系。结果表明,在不同固结压力作用下,固结完成后的不排水抗剪强度与有效应力呈现出传统的线性关系,但是,在某一固结压力作用下,固结过程中的不排水抗剪强度却随有效应力的增长呈非线性增长,而且,在不同固结压力作用下,固结压力越大,固结过程中达到相同的有效应力时所对应的不排水抗剪强度越大。固结过程中的不排水抗剪强度并不仅仅取决于剪前固结有效应力,还与剪前孔隙比相关,孔压消散速率小于变形速率是导致固结初期、剪前固结有效应力较小时,不排水抗剪强度较快增长的主要原因。

Behavior of undrained shear strength of saturated soft clay under consolidation

By integrating the functions of large-diameter consolidometer and miniature vane shear devices, a systematic apparatus is devised and developed to be capable of performing shear tests at any point in time during the consolidation process of saturated soft clay. Considering the non-uniformity change of the excess pore-water pressure in space and time, each miniature vane shear device is equipped with a miniature pore-water pressure transducer at the bottom of its hollow axial shaft mounting blades. The large-diameter consolidometer is equipped with miniature earth pressure cells. Thus the apparatus has a function of automatic real-time monitoring of changes of the effective stresses at the positions of vane shear tests. By using this systematic apparatus, the vane shear tests are carried out at different points in time during the consolidation process of saturated soft clay subjected to different consolidation pressures. The changes of real-time deformation and pore-water pressure are monitored during the consolidation process, and the effective stresses and the undrained shear strengths at the positions of vane shear tests are derived. The correlation between the shear strength and the effective stress is analyzed. It is shown that the traditional linear relationship exists between the undrained shear strengths at the end of consolidation under different pressures and effective stresses. However, under a certain consolidation pressure, the shear strength increases non-linearly with the increase in the effective stress during the consolidation process. Moreover, under different consolidation pressures, the larger the consolidation pressure, the higher the shear strength at the same effective stress generated during the consolidation process. The undrained shear strength gained during consolidation is dependent on the effective stress and the void ratio before shearing. The fact that the rate of dissipation of pore-water pressure is less than the rate of deformation is the main reason for the rapid increase in the undrained shear strength at the early stage of consolidation when the effective stress before shearing is relatively low.