钙质砂三轴排水试验围压与剪切速率对应力特性影响研究

Influences of confining pressure and shear rate on stress characteristics of triaxial drainage tests on calcareous sand

以海南省三沙市西沙群岛钙质砂为研究对象开展不同剪切速率的三轴固结排水试验,研究钙质砂剪切应力特性。试验结果表明:围压越大偏应力峰值出现的越晚,相同围压剪切速率越快应力峰值越大,应力下降也越快应力下降比越大,剪切速率对应力的峰值大小及残余剪切强度有一定影响,低围压下剪切速率对偏应力峰值影响更大。围压越小偏应力比越大,相同围压剪切速率越大偏应力比增长越快,当剪切速率低于一定速度时,偏应力比的变化并不受剪切速度的影响。相同围压条件下,由于排水剪切时围压和孔压保持不变,偏应力和平均有效应力关系为斜率3的直线,不同剪切速率破坏线趋势相同,剪切速率越大破坏线角度越大,但相差不大,破坏线为接近斜率1.75的直线,钙质砂内摩擦角为42°。剪切过程平均有效应力先增大后减小,剪切过程表现出剪缩到剪胀的变化过程,剪缩阶段不同剪切速率下孔隙比下降速率相近,剪切速率在剪胀阶段对孔隙比影响较大,剪切速率越大,孔隙比变化越大。

The triaxial consolidation drainage tests with different shear rates are carried out to study the shear stress characteristics of the calcareous sand in Xisha Islands,Sansha City,Hainan Province of China.The test results show that the larger the confining pressure is,the later the peak value of the deviator stress appears,and the faster the shear rate of the same confining pressure is,the larger the peak value of the stress is,the faster the stress drop is,the larger the stress drop ratio is,the shear rate has a certain effect on the peak value of the stress and the residual shear strength,and the lower the confining pressure is,the greater the impact of the shear rate on the peak value of the deviator stress.The smaller the confining pressure,the larger the deviator stress ratio,and the larger the shear rate of the same confining pressure,the faster the deviator stress ratio increases.When the shear rate is lower than a certain rate,the change of the deviator stress ratio is not affected by the shear rate.Under the same confining pressure,because the confining pressure and pore pressure remain unchanged during drainage shear,the relationship between the deviatoric stress and the average effective stress is a straight line with slope of 3,and the trend of failure line is the same at different shear rates.The larger the shear rate is,the larger the failure-line angle is,but the difference is not large.The failure line is a straight line with slope of 1.75,and the internal friction angle of the calcareous sand is 42°.The average effective stress increases first and then decreases during the shearing process,which shows a change process from shear shrinkage to dilatancy.The pore ratio decreases under similar rates at different shear rates at the shrinking stage.The shearing rate has a greater influence on the pore ratio at the dilatancy stage.The larger the shear rate is,the larger the change of the pore ratio is.