考虑结构性影响的原状软黏土应力–应变特性真三轴试验研究

通过对营口原状软黏土和饱和重塑软黏土的真三轴试验,研究围压和中主应力系数对软黏土强度的影响。基于综合结构势理论,提出真三维应力条件下软黏土的应力比结构性参数,建立引入结构性参数的原状软黏土偏应力–广义剪应变关系式。研究结果表明:当固结围压先期固结压力时,原状软黏土偏应力–广义剪应变曲线形态表现为应变软化,体应变表现为剪缩特性;当固结围压先期固结压力时,其曲线形态表现为应变硬化,体积应变表现为剪胀特性;饱和重塑软黏土的偏应力–应变关系曲线则不受先期固结压力的影响,均表现为应变硬化型。软黏土强度都随着固结围压和中主应力系数的增大而增大。应力比结构性参数m_η随广义剪应变、固结围压和中主应力系数的增大而降低,其与广义剪应变呈显著的对数关系。将拟合得到的应力比结构性参数m_η引入到原状软黏土的q-ε_s曲线中,得到q/m_η-ε_s关系曲线,进而建立引入结构性参数的原状软黏土偏应力–广义剪应变关系式,其与试验结果具有较好的一致性,从而使原状软黏土q-ε_s曲线得到合理描述。

True triaxial tests on stress-strain characteristics of soft clay considering the structural effects

The true triaxial tests to the undisturbed and the saturated remould soft clay from the city of Yingkou were carried out to study the effect of confining pressure and principal stress on the strength of soft clay. The stress ratio of soft clay under the three-dimensional stress conditions is presented according to the comprehensive structure potential theory and the relationship between the deviatoric stress and the generalized shear strain of the undisturbed soft clay with structural parameters is established. The curve of the deviatoric stress(q) vs the generalized shear strain( ) of undisturbed soft clay is related to the pre-consolidation pressures. It is strain softening when the confining pressures are smaller than the pre-consolidation pressures and the volumetric strain appears shear shrinkage. It is strain hardening when the confining pressures are larger than the pre-consolidation pressures and the volumetric strain appears shear dilation. The type of curves of q vs. of the disturbed saturated soft clay is not affected by the structural yield stress and is basically the strain hardening one. The strengths of undisturbed soft clay and saturated soft clay are increased with the increasing of the confining pressure and coefficient of the principal stress. But the structural parameters of stress ratio decreased with the increasing of the shear strain，confining pressure and coefficient of the principal stress. The structural parameters of stress ratio varies logarithmically with the generalized shear strain. The structural parameters of stress ratio was introduced into the q- curves of undisturbed soft clay and the curves were thus obtained. The relationship between the deviatoric stress and the generalized shear strain for undisturbed soft clay was established and it has a good agreement with the experimental results.