冻融循环下青藏粉砂土双屈服面本构模型研究

基于青藏粉砂土在冻融循环下的常规三轴固结剪切试验,通过引入模量残余比和冻融循环次数,建立考虑冻融循环影响的双屈服面本构模型。试验结果表明,粉砂土的应力–应变关系呈应变硬化型,而在整个剪切过程中,体变呈现剪缩的特性。粉砂土的剪切模量随着围压的增大而增大,随着冻融循环的发展而出现先减小后增大的趋势。与未冻融粉砂相比,冻融以后的弹性剪切模量可降低约36%左右。其应力平面p-q上的剪切屈服面和体积屈服面可分别用过原点的线性函数和椭圆型曲线进行描述。对于剪切和体积硬化特性,建立与塑性应变及冻融循环次数相关的硬化参数,且均采用非相关联的流动法则。所提出的双屈服面本构模型能够很好地反映土体的应力–应变特性,模型计算值与试验值较为吻合,该模型能较为准确地预测不同围压及不同冻融循环次数下的应力–应变关系曲线,较好地反映冻融循环对粉砂力学性质的影响。

A constitutive model with double yielding surfaces for silty sand after freeze-thaw cycles

Based on the consolidated drained triaxial test on silty sand after freeze-thaw cycles，a constitutive model with double yielding surfaces was established by introducing the residual ratio of shear modulus and the numbers of freeze-thaw cycles. The experimental results showed that the stress-strain relationships exhibited strain hardening properties while the volumetric strain appeared shear contraction during the shearing process. The elastic shear modulus increased with the confining pressure but decreased firstly and then increased with the numbers of freeze-thaw cycles. The shear modulus dropped about 36% compared with the unfrozen silty sand. The shear yielding surface was expressed as a linear function cross the origin，while the volumetric one was represented as an elliptic curve. The shear and volumetric hardening parameters were related to the plastic strain and the numbers of freeze-thaw cycles and the non-associated flow rule was adopted. The proposed constitutive model with double yielding surfaces was verified by comparing the modeling results with the triaxial test results. The stress-strain curves predicted by the proposed model agreed well with the experimental results for both the unfrozen silty sand and the samples experiencing freeze-thaw cycles.