不同应力条件下土体渐进破坏过程模拟及机理研究

In geothchnical engineering, most issues were investigated and attributed to deformation and strength problems. When undergoing loading, the failure process of soil exhibits progressive character, thus, progressive failure theory was consideres as one of the three basic theory on modern soil mechanics, correlation study also became a hot spot as well as a difficult point in geotechnical engineering. By carefully review of relative studies, limitations and deficiency on the research of progressive failure mechanism and process simulation of soil body could still be found, thus, study on this issue is still needed.In this project, the progessive failure process of soil will be studied by both theory researching and numerical simulating. The specific research contents are as follows: (1) Numerical simulation of progressive failure on soil unit. A numerical algorithm considering strain softening as well as mesh dependence problem will be proposed, the empirical value of the factor in damp newton method will be studied, together with the relationship between internal character length and mesh size. (2) Analysis on progressive failure mechanism of soil.The creation conditions and development mechanism of strain localization will be studied,and stress transfer mechanism based on energy transmission for progressive failure process will be proposed. (3) Simulation of progressive failure process and analysis on stability of 3D slope. A typical slope will be analysised based on the 3D programe of gradient plastic theory. The results of this research will develop the progressive failure theory of soil, and provide theoretical basis for the failure process analysis of soil.

多数岩土工程问题都可归结为岩土体的变形和强度问题，土体在荷载作用下的破坏过程具有明显的渐进性，岩土体的渐进破坏理论是现代土力学三个基本理论之一，相关研究也成为岩土领域的热点与难点问题，但土体的渐进破坏机理和过程模拟都还存在局限和不足，故本项目针对这一主题开展系统研究，从理论研究和数值计算方面研究土体渐进破坏过程。研究内容包括：（1）土单元渐进破坏过程模拟，提出考虑应变软化计算和网格依赖性问题的有限元算法，研究阻尼牛顿算法中阻尼因子的经验选取，以及梯度塑性理论中内部特征长度与网格尺寸的关系；（2）土体渐进破坏机理分析，研究应变局部化区域的启动和发展机理，提出渐进破坏过程中应力按照能量方式的传递机理；（3）三维边坡的渐进破坏过程模拟及稳定性分析，基于自编有限元程序进行三维边坡算例分析。研究成果将发展土体渐进破坏理论，并对土体破坏过程分析提供理论依据。

进入21世纪，随着地下空间的大规模开发，城市施工环境复杂，技术难度大，安全风险高等因素引起的灾害事故较多，造成巨大的经济损失和人员伤亡。多数地下工程事故都可归结为岩土体的变形和强度问题，土体在荷载作用下的破坏过程具有明显的时空渐进性，但因为岩土本是一种不均匀的散体材料，加之地下工程环境条件复杂，所以不同应力条件下岩土体渐进破坏理论研究和模拟研究都还存在不足。本项目针对这一主题开展系统研究，研究内容和结果包括：（1）土体渐进破坏过程模拟算法研究。提出考虑应变软化和网格依赖性问题的有限元算法，使用阻尼牛顿算法计算应变软化，使用梯度塑性理论解决网格依赖性。对阻尼因子的物理意义进行研究。阻尼因子的选取因计算问题不同，从土单元到土坡软化可以取3.5，硬化部分参数可取2.0。内部特征长度参数粉质黏土可取10粒径。（2）土体渐进破坏过程机理分析，研究应变局部化区域的启动、发展机理和破坏模式。从本构模型、剪胀性、排水条件、中主应力、边界条件和初始均匀性等多角度激发数值模拟中的应变局部化启动。与三轴应力路径试验结果拟合。提出渐进破坏过程中应力按照能量方式的传递机理。在应变局部化发展过程中进行了大量的随机缺陷模拟研究，得到了不同缺陷分布条件下的多种破坏模式。剪切带形式有单一、交叉等多种，宏观剪切带在经过竞争机制后的最终破坏模式与整体边界条件的对称性相关。（3）不同应力条件下土坡体渐进破坏过程模拟研究。对三维土质边坡、加固边坡及基坑进行了模拟算例的研究，考虑了初始不均匀性、支护方法和施工步骤等因素。对土体与结构共同作用情况，潜在滑裂面的变形过程进行了预测与分析。该项目研究成果发展了土体渐进破坏理论，解决了应变软化和依赖性的模拟问题，对变形过程的阶段划分为指导工程进行土体变形预测和破坏过程分析提供理论依据。