非饱和土时效性和本构关系研究

The stress-strain behavior of soil is non-linear and associated with its time-dependent property. Residual ground settlement/foundation settlement induced by the time-dependent behavior /viscosity of soil will cause failure of infrastructures, which has gained concern worldwide. Time-dependent behaviors of saturated soils mainly consist of creep, swelling, relaxation, strain-rate effect and long-term strength while for unsaturated soils, the behaviors could be much complex due to the influence of matrix suction and variation of porewater pressure. Current study on the unsaturated soil lacks of systematic experimental and theoretical analysis and this proposal aims to fill this gap. Through laboratory and theoretical studies on typical Shanxi loess, the 1D to generalized 3D time-dependent stress-strain property will be clarified. Under Ko consolidation, the constitutive model of unsaturated soils can be built, which will be further validated by indoor strain-rate tests. Emphasis will be also placed on the anisotropic and deformation properties of unsaturated soils. Incorporated with development of constitutive model in finite element software, the fully-coupled analysis can be carried out to predict the in-situ settlement/collapse of loess or make comparison so that the effectiveness of the model can be examined. This proposal is solid based on the fundamental investigation of soils, has factual engineering background and research value. The outcome of the study will supplement experimental data for unsaturated soils and provide scientific evidence for site practice.

土的应力应变关系是非线性的，与时效性密切相关。土的时效性/粘性特征引发的残余的地面/地基沉降造成的地上土工结构破坏已经引起各地乃至世界工程界的关注。土的时效性主要包括蠕变、膨胀、应力松弛、应变率效应及长期强度，而对于非饱和土而言，由于基质吸力和孔隙压力变化导致的时效特征更为复杂。本项目鉴于当前对非饱和土时效性研究缺乏系统的实验数据和理论分析，以山西典型的非饱和黄土为研究对象，通过实验研究和理论分析手段，旨在揭示黄土一维到三维的应力应变时效特征；在Ko固结的基础上，建立适合非饱和土的本构关系，并通过室内应变率实验进行验证；研究还将重点分析非饱和土的各向异性和变形特征，结合有限元软件的本构模块开发，进行完全耦合分析，预测和比对黄土的沉降和湿陷性特征，检验模型的有效性。本项目根植于土的基础研究，具有实际的工程背景和研究价值，项目成果将会丰富非饱和土研究的实验数据，为工程实践提供科学依据。

土的时效性主要包括蠕变、膨胀、应力松弛、应变率效应及长期强度，而对于非饱和土而言，由于基质吸力和孔隙压力变化导致的时效特征更为复杂。本课题针对山西地区典型原状黄土和重塑黄土，通过本实验研究和理论分析两部分，分析黄土应力应变关系和时效性特征。实验部分包括土的一维、二维的常规固结实验以及蠕变实验，应变率试验和不同的应力路径实验。结合室内实验绘制了应力应变关系曲线，探讨了不同应力状态下黄土的应变特征以及主要的影响参数，探讨了增水和减水作用下压缩量的变异特性。分析了不同固结条件、应力路径对试样的强度、变形、孔隙水压力的影响规律，研究了不同的施工工况对应三轴应力路径下的黄土的强度的变化。结合实验结果对黄土的蠕变特性进行了广泛的探讨，对表征黄土特性的参数cv, cc, cα以及cu/Eu等进行研究，同时比对饱和/不饱和试样的特征曲线，比对重塑土/原状土的水敏特性。本课题重点分析非饱和土在压力作用下的时效性变形特征，结合有限元软件的数值模拟，验证了土体参数，预测和比对黄土的压缩特征，并模拟了应力率实验，分析了应力应变关系以及孔隙水压力的变化。本项目根植于土的基础研究，具有实际的工程背景和研究价值，项目成果将会丰富非饱和土研究的实验数据，为工程实践提供科学依据。由于设备开发问题以及在实验中取得的数据未达预期，本课题未能提出适合山西地区黄土变形的有效应力本构方程。