K_0固结后卸载状态下冻土应力-应变特性研究

STUDY ON BEHAVIOR OF STRESS-STRAIN FOR FROZEN SOILS SUBJECTED TO K_0 CONSOLIDATION BY UNLOADING TRIAXIAL SHEAR TESTS

通过模拟人工冻结凿井中土体固结、冻结、受力的实际过程,研究了经K0固结后兰州冻结黄土在径向卸载状态下的应力-应变行为,并利用试验资料所建立的数学方程研究了K0固结后冻土的初始切线模量Ei和主应力差渐近值(s1-s3)ult与初始围压s3、温度的关系。结果发现,K0固结后再冻结的黄土试样在整个卸载过程中,其特征类似于理想刚塑性应力-应变曲线;初始围压s3的升高和温度的降低都可以使深部冻土抵抗变形的能力增强。因此,当深度一定时,应先考虑深度对强度影响后再选择最优温度来满足此深部土体卸载时的强度要求;初始弹性模量Ei在较低负温、较高初始围压状态下,不随初始围压s3而变化,且趋近于一常数;(s1-s3)ult随初始围压s3的增大而线性增大,在较低初始围压状态下受温度影响较小,随着初始围压的增高,受温度影响逐渐明显;可利用主应力差渐近值(s1-s3)ult与破坏比之间的关系来估算破坏强度的大小。

In order to determine the behaviour of stress-strain of frozen soil in the deep alluvium,the triaxial unloading shear tests at temperature of -2 ℃,-5 ℃,-7 ℃,-10 ℃ and a confining pressure of 1～5 MPa were performed in cold laboratory after specimen experienced K0 consolidation. The testig results indicate that the radial unloading stress-strain curves can be divided into three different stages,that is,elastic stage,strain-hardening stage and the yield stage or flow stage. There is no displacement at a lower negative temperature and somewhat higher initial confining pressure,even if the confining pressure is removed to zero. The failure strength increases with the initial confining pressure increasing and the temperature decreasing. From the stress-strain equation of tested frozen soil,the ultimate principal stress difference (s1-s3)ult and the initial tangent modulus Ei can be obtained. The initial tangent modulus Ei does not depend on the initial confining pressure and is close to a constant at a state of lower negative temperature and higher initial confining pressure. The ultimate principal stress difference (s1-s3)ult increases linearly with increment of initial confining pressure and the role of temperature is not obvious at lower initial confining pressure. However,with the confining pressure increasing,it becomes pronounced gradually.