考虑小应变刚度特性的软土边界面模型与应用

Bounding surface constitutive model for soft soils considering characteristics of small-strain stiffness and its application in engineering

基坑开挖导致周边土体经历复杂的加卸载应力路径,传统的本构模型难以同时反映此过程中土体的超固结和小应变刚度特性。在现有的边界面模型中,引入土体小应变刚度特性,提出软土边界面模型小应变刚度修正方法。基于一种高效的半隐式应力更新算法,将改进后的边界面模型采用UMAT子程序二次开发嵌入有限元软件ABAQUS中,并应用于某地铁车站深基坑开挖工程的数值模拟。分析结果表明,采用改进模型准确地反映了上海地区典型土层的小应变状态本构关系和土体的应变刚度相关性;由于改进的边界面模型能够同时反映土体超固结和小应变刚度特性,计算的围护结构变形与现场监测数据吻合较好。

The construction of an excavation pit induces complex loading-unloading stress paths in the surrounding soils,while the commonly used constitutive models are insufficient to reflect the over-consolidation and small-strain stiffness characteristics during excavation.In this study,a modified bounding surface model considering the over-consolidation and strain-stiffness relationship of soft soils is proposed by modifying the shear modulus under small-strain state.Based on the user defined material subroutine(UMAT),the modified bounding surface model is developed into the finite element software ABAQUS through an accurate and efficient semi-implicit stress update algorithm,and the numerical simulation is carried out for a deep excavation of underground station.The constitutive relationship of typical Shanghai soil under small-strain state is well predicted by the proposed model.The stress-strain curve results show that the proposed model reflects the relationship between soil strain and stiffness reasonably.Since the modified bounding surface model reasonably reflect the over-consolidation and small-strain stiffness characteristics of soil in the same time,the numerical simulation results by the proposed model satisfy the field data.