土体三维卸荷弹塑性模型及其试验验证

Three-dimensional elastoplastic model of soil with consideration of unloading stress path and its experimental verification

天然土体经历开挖卸荷应力路径后,其应力变形特性与常规加载应力路径条件下规律存在较大差异。目前常用土体本构模型大多建立在等向固结单向加载三轴试验基础上,没有考虑初始K_0固结和开挖卸荷应力路径的影响。以剑桥模型为基础,借鉴关口-太田模型的建模思想,通过引入新的应力比参数,对p-q平面上屈服轨迹硬化轴进行旋转,调整弹性区范围,以反映初始K_0固结的影响;再运用变换应力法将模型三维化处理,从而使模型可以描述土体三向不等向应力状态,最终得到一个能综合反映土体K_0固结开挖卸荷应力-应变特性的三维弹塑性本构模型。通过和典型室内应力路径试验结果进行对比,验证了模型的合理性。

When the natural soil is influenced by the unloading induced by the excavation,its stress-strain relationship shows a quite difference with the relationships obtain from the conventional loading test of undisturbed natural soil.At present,commonly applied soil constitutive models are established based on the conventional tri-axial test,where soil is subjected to isotropic confine pressure and uni-axial loading stress.In addition,these constitutive models do not take the influence of initial K0 consolidation and the unloading induced by excavation into consideration.In this paper,a new model is proposed based on the Cam-clay model and the principles of Ohta-Sekiguchi model.In the proposed model,to adjust the elastic region and reflect the influence of the initial K0 consolidation,the hardening axis in p–q stress space is rotated by introducing a stress ratio.To describe the three-dimensional anisotropic stress state,the transformation stress method is introduced to the model.By all these approaches above,this newly proposed model is able to reasonably describe the strength and deformation of soil under initial K0 stress and complex stress-train relationships under unloading induced by excavation.The rationality of this proposed model is verified by comparing the predicted results with the results obtained from typical laboratory tests.