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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。
Based on the conventional triaxial consolidation shear tests of Qinghai silt sand under freeze-thaw cycles, a dual yield surface constitutive model considering the effects of freeze-thaw cycles was established by introducing the modulus residual ratio and the number of freeze-thaw cycles. The test results show that the stress-strain relationship of silty sand is in the form of strain hardening, while the body shear shows the characteristics of shearing during the whole shearing process. The shear modulus of silt soil increases with the increase of confining pressure. With the development of the freeze-thaw cycle, the shear modulus of the silt decreases first and then increases. Compared with unfrozen silt, the elastic shear modulus after freezing and thawing can be reduced by about 36%. The shear yield surface and volume yield surface on the stress plane p-q can be described by a linear function over the origin and elliptic curve, respectively. For the shear and volume hardening characteristics, the hardening parameters related to the plastic strain and the number of freeze-thaw cycles are established, and non-correlated flow laws are used. The proposed dual yield surface constitutive model can well reflect the stress-strain characteristics of soil, and the calculated values are in good agreement with the experimental values. The model can accurately predict the stress under different confining pressures and different freeze-thaw cycles - strain curve, a good reflection of the freeze-thaw cycle on the mechanical properties of silt.