孔隙水压作用下隧道围岩的卸荷蠕变特性

Unloading creep characteristics of tunnel surrounding rocks under pore water pressure

隧道开挖后围岩体在卸荷及孔隙渗流作用下发生变形。通过不同孔隙水压作用下砂岩的三轴卸荷蠕变实验,分析了砂岩的蠕变特征、瞬时应变特征及蠕应变变化特征。结果表明:相同荷载水平下,孔隙水压越大,蠕变破坏所需时间越短,试样的变形量越大,变形能力越强,最终破坏荷载水平越小。在最后一级荷载水平作用下,无孔隙水压作用下砂岩试样的加速蠕变曲线相对缓和,随着孔隙水压的逐渐增大,试样的加速阶段曲线逐渐变陡;随着孔隙水压的逐渐增大,砂岩试样的轴向应变、横向应变均呈逐渐递增趋势,且增幅逐渐减小;试样的蠕应变随孔隙水压呈逐渐递增趋势,且荷载水平越高,曲线的斜率越高,表明孔隙水压对砂岩蠕应变的影响越显著。砂岩的卸荷瞬时应变与蠕应变的比值同样随孔隙水压的增大呈逐渐递增趋势。

This paper is an attempt to address the deformation of surrounding rock mass under unloading and pore seepage following tunnel excavations.The study involves performing a triaxial creep test of sandstone under different pore water pressure and analyzing the variation characteristics of creep curve,instantaneous strain and creep strain of sandstone.The results show that,under the same load level,the larger the pore water pressure is,the shorter the creep failure time is,the larger the deformation amount and the stronger the deformation capacity of the specimen are,and ultimately,the smaller the final failure load level is;under the horizontal action of the last stage of load,the accelerated creep curve of sandstone samples without pore water pressure is relatively moderate and the gradual increase of pore water pressure is followed by the gradually steepening accelerated creep curve of sandstone samples;along with the gradual increase of pore water pressure,there emerges a gradual increasing trend in the axial strain and transverse strain of sandstone samples,during which the increase gradually decreases;and the creep strain of the sample tends to increase gradually with the pore water pressure,and the higher the load level is,the higher the slope of the curve is,showing a more significant effect the pore water pressure has on the creep strain of sandstone.There is a gradual increases in the ratio of unloading instantaneous strain to creep strain of sandstone with the increasing pore water pressure.