超孔隙水压力对低塑性黏性土桩土界面抗剪强度的影响

Influence of excess pore water pressure on shear strength of pile-soil interface in clayey soil

研究黏性土中桩土界面的抗剪强度及其参数受超孔隙水压力影响的规律,对工程实践具有重要意义。利用自制的大型恒刚度直剪仪,完成了一系列不同界面粗糙度、不同试样含水率和不同剪切速率试验条件下的直剪试验,分析了在不同试验条件下超孔隙水压力变化规律,进而得到考虑超孔隙水压力的桩土界面抗剪强度及其参数的变化规律。研究结果表明:随着界面粗糙度等级提高,桩土界面超孔隙水压力减小,桩土界面抗剪强度、有效黏聚力和有效摩擦系数增加;随着含水率的增加,桩土界面超孔隙水压力增加,桩土界面抗剪强度降低,含水率对桩土界面抗剪强度的影响主要是改变了桩土界面的黏聚力,黏聚力先增大后减小,对摩擦系数的影响较小;特定试验条件下,随着剪切速率的增加,桩土界面超孔隙水压力增加,桩土界面抗剪强度降低,桩土界面黏聚力先增大后又减小,变化幅度不超过2 k Pa,对摩擦系数的影响较小。因此,桩土界面抗剪强度及其参数是界面粗糙度、试样含水率和剪切速率变化引起超孔隙水压力变化共同影响的结果,试验结果可供相关工程设计参考。

It＇s important to study the variation of shear strength and parameters of pile-soil interface for clayey soil with the excess pore water pressure in engineering practice. A series of direct shear test with different interface roughness, water contents and shearing rates is performed using the large-scale direct shear apparatus with constant normal stiffness. The effect on excess pore water pressure is examined under different test conditions. Influence of excess pore water pressure on shear strength of pile-soil interface in clayey soil is obtained. The results show that the excess pore water pressure decreases, and the shear strengths of pile-soil interface, effective cohesion and effective coefficients of friction increase with the increasing interface roughness. The excess pore water pressure increases and the shear strength of pile-soil interface decreases with the increasing water content. The main influence of increasing water content on shear strength of pile-soil interface is changing the cohesion. The cohesion first increases and then decreases. The influence on the coefficients of friction of pile-soil interface is little. The excess pore water pressure increases and the shear strengths of pile-soil interface also decrease with the increasing shear rate. The cohesion of pile-soil interface first increases and then decreases, but the variation is less than 2 k Pa, and the little influence on the coefficients of friction of pile-soil interface. The change of shear strength and parameters is influenced by variation of excess pore water pressure, depending on interface roughness, water contents and shear rates. This experimental research is useful for relative engineering design.