考虑小应变特性的土的本构关系研究

The stress-strain characteristics at small strains are called small strain behaviors. The engineering properties of soils at small strains are different with the understanding of those in the past. The prediction and evalution of some engineering problems, such as soil-structure interaction and strict deformation control, will be distorted by models which cannot describe the small strain behaviors. In recent years, numerous experimental studies on small strain behaviors have been conducted. A number of constitutive models have been developed to describe small strain behaviors of soils. Several of the existing models are elastoplastic models. Those elastoplastic models considering small strain behaviors cannot describe the strain-softening/shear-dilatancy or have many parameters which make the model hard to be applied in practical engineering. Based on the small-strain-included tests, this project plans to study small strain behaviors of soils by conducting essential tests. A hysteretic stress-strain relationship will be formulated to describe the small strain behaviors and one-dimensional compression bahaviors for clay and sand. Besides, the hysteretic stress-strain relationship need to be worked with the overconsolidated clay model (UH Model) proposed by the applicants, and then an elastoplastic model which will be able to describle entire strain range behaviors of clay and sand will be developed. Finally the proposed model will be incorperated into the finite element analysis software to simulate practical problem of geotechnical engineering.

土在小应变范围内的应力应变特性称为小应变特性。在实际工程中，如不考虑土的小应变特性将会严重影响本构模型对某些工程问题的预测和评估，如：地基不均匀沉降、隧道或基坑开挖对周围环境的影响等。近年来，人们针对砂土和黏土的小应变特性进行了大量的试验研究，但在考虑小应变特性的弹塑性本构模型研究上仍处于初级阶段。目前的能反映小应变特性的本构模型以非线性弹性模型为主，现有的少数考虑小应变特性的弹塑性本构模型要么不能反应软化、剪胀等特性，要么参数繁多缺乏实用性。本项目拟在深入研究砂土和黏土小应变特性的基础上，构造能考虑小应变特性的统一描述砂土和黏土一维压缩特性的应力应变滞回关系，最后与申请者提出的超固结土弹塑性本构模型结合，建立简单实用的能考虑小应变特性的统一弹塑性本构模型，实现对砂土和黏土在全应变范围内力学特性的统一描述，并使用变换应力实现模型的三维化，最后将模型嵌入到有限元程序以模拟实际的岩土工程问题。

在实际工程中，如不考虑土的小应变特性将会严重影响本构模型对某些特殊工程问题的预测和评估，如：地基不均匀沉降、隧道或基坑开挖对周围环境的影响等。目前能反映小应变特性的本构模型以非线性弹性模型为主。本研究深入研究了土的小应变特性、低围压下粒状土的特性、砂土和黏土的应力应变特性等。构造了能考虑小应变特性的统一描述黏土一维压缩特性的应力应变滞回关系，引入压硬性参量描述粒状土在超低围压条件下极小的可压缩性，与申请者已提出的超固结土弹塑性本构模型结合，建立了简单实用的能考虑小应变特性的UH模型、考虑低围压的粒状土的UH模型、黏土和粒状土统一的UH模型等。实现了对土在全应变范围内力学特性的统一描述。还在经典强度准则和统一硬化模型的基础上，发展了各向异性强度准则和本构模型，并将其应用于模拟由各向异性引起的更为复杂的应力应变特性，使用变换应力实现模型的三维化。将模型嵌入到有限元程序模拟堆载对高铁路基变形影响、黄土隧洞变形稳定性分析等实际的岩土工程问题。相关成果为岩土工程的分析计算提供了坚实的理论基础。