南海饱和软土单剪强度试验研究

A study of direct simple shear strength for South China sea clay

采用应力控制的单剪试验对中国南海海域原状饱和软黏土的力学响应进行了研究,考察了不同应力水平下软黏土的应力应变响应和强度特征。结果表明:无初始剪应力时,当应变小于5%时,循环应变增长缓慢且稳定,超过5%以后,循环应变迅速增长并达到破坏标准,因此可将循环应变达到5%作为破坏标准,同时,动应力比存在阈值,当动应力比小于0.52时,认为土体不会发生破坏;有初始剪应力时,应变向有初始应变一侧累积,且无论是增加静应力比还是动应力比,都会引起应变累积加快,破坏振次减小,相对而言,动应力比对累积应变和破坏振次的影响更明显。最后给出了破坏振次为1 000次的强度包线,提供了安全的静、动应力比组合方式。

Several stress-controlled static and dynamic direct simple shear tests were conducted to study the strength characteristics of the soft saturated clay obtained from the South China Sea. The experimental results in this study show that under the condition without initial shear stress,the cyclic strain increases slowly and steadily with the cyclic number when it is less than 5%,and increases rapidly and reaches the failure when it exceeds 5%,thus 5%of the cyclic strain can be the strain failure criterion. Moreover,the dynamic stress ratio has a threshold 0. 52 and the soil will never be destroyed when the dynamic stress ratio is less than the value. The cyclic strain would be accumulated to the side of the initial strain under the initial shear stress. Both the static stress ratio and dynamic stress ratio can improve the accumulative pace of the shear strain and decrease the number of cycles to failure,but the effects of the latter are more significant than the former. The strength envelope of 1 000 times to failure is presented,which provides a safety combination of the static and dynamic stress ratio.