考虑超孔隙水压力的桩土界面直剪试验研究

Research on effect of pore water pressure on shear test of pile-soil interface

采用大型恒刚度直剪仪,系统研究超孔隙水压力对黏性土中桩土界面剪切性能的影响。根据制定的测试超孔隙水压力方案,对4个粗糙度等级(混凝土表面锯齿状峰谷距为0、2、4、6 mm)的不同含水率黏性土中桩土界面在不同剪切速率下进行剪切试验。针对界面粗糙度、黏性土含水率、剪切速率3个变化参数对界面抗剪强度的影响进行分析。结果表明:界面粗糙度越大,界面超孔隙水压力越小,有效法向应力越大,黏性土颗粒与混凝土表面吸附性越大,桩土界面抗剪强度越大;黏性土含水率越大,界面超孔隙水压力越大,有效法向应力越小,黏性土颗粒与混凝土表面吸附性不能完全发挥,桩土界面抗剪强度反而减小;在剪切速率0.4~1.0 mm/min范围内,剪切速率越大,界面超孔隙水压力增幅较小,有效法向应力变化不大,桩土界面抗剪强度虽有减小,但不同剪切速率下超孔隙水压力对桩土界面抗剪强度的影响不明显。

A series of direct shear tests were carried out to study the effect of pore water pressure on shear performance of pile-soil interface. The pile-soil interfaces of different roughness ( concrete interface sawtooth peak-valley distance of 0,2 ,4 ,6 mm,respectively) were tested in clayey soil under different shear rates during shearing according to the schemes of testing pore water pressure. Results are presented for interface shear behavior under three parameters of interface roughness,water content in clayey soil and shear rate. Results show that the lower pore water pressure is resulted from higher interface roughness,the effective normal stress is higher,and the higher shear strength of pile-soil interface is resulted for higher suction between concrete and clayey soil;the higher pore water pressure is resulted from higher water content in clayey soil,the effective normal stress is lower,and the lower shear strength of pile-soil interface is resulted while the suction decreases between concrete and clayey soil;in shear rate range of 0. 4- 1. 0 mm/min,the increase of pore water pressure is smaller with higher shear rate in clayey soil,the effective normal stress has a little change,and shear strength of pile-soil interface decreases,but the effect on shear strength of pore water pressure under different shear rates is not obvious.