基于干湿循环稳定状态的膨胀土变形机理与本构模型研究

The swelling-shrinkage equilibrium state, which expansive soils will reach after experiencing several wetting-drying cycles, provides a theoretical basis for developing new modeling framework for expansive soils. Unfortunately until now there are no systematic experimental and theoretical achievements on the swelling-shrinkage equilibrium state of expansive soils. Through a series of suction-controlled cyclic wetting-drying tests as well as post-cyclic compression tests both on intact and remolded expansive soil samples, this study will focus on: 1) revealing the physical mechanism, influence factors and specific pattern of the swelling-shrinkage equilibrium state, 2) elucidating the intrinsic relation of the apparent swelling-shrinkage behavior to the microscopic and mesoscopic structure of expansive soils; and 3) seeking a decomposition methodology and providing its corresponding descriptions for the apparent swelling-shrinkage deformation. After that, a constitutive model within the framework of the swelling-shrinkage equilibrium state theory will be proposed and a numerical procedure will be developed for evaluating the deformation and stability of expansive soil foundations. The expected achievements will be conductive to geological hazard evaluation and prevention in expansive soil areas.

干湿循环作用下，膨胀土在发生不可逆的结构调整后将达到一个干湿稳定状态，该状态决定了膨胀土在干湿循环作用下的最终变形形态。干湿循环稳定状态对于发展新的膨胀土本构理论框架具有重要价值，但目前还缺乏系统的试验和理论研究成果。本项目拟通过系统的原状膨胀土和重塑膨胀土的干湿循环试验和干湿循环后的加载试验，重点解决：（1）干湿循环稳定状态的物理机制、影响因素和具体形式；（2）宏观胀缩变形规律与膨胀土微、细观两个结构层次的内在联系；（3）膨胀土宏观胀缩变形的分解机制和描述方法。在此基础上，发展基于稳定状态的非饱和膨胀土本构模型，开发可用于膨胀土地基变形评估的计算软件。研究成果可助益于我国膨胀土地区的地灾防治和工程建设评价。

已有试验现象表明，击实膨胀土在经历一定次数的干湿循环后将达到干湿胀缩变形基本可逆的一个稳定状态。该状态决定了膨胀土在干湿循环作用下的最终变形，对于发展新的膨胀土本构理论框架具有重要价值。然而，鉴于膨胀土的干湿循环试验耗时费力，目前还缺乏系统的试验和理论研究成果。. 针对上述问题，本项目主要在以下方面取得了进展。（1）分别开展了含水量控制和吸力控制的击实膨胀土干湿循环试验，系统地研究了荷载水平和干湿路径对干湿胀缩变形和稳定状态的影响；（2）基于试验成果，理论上分析了膨胀土的双重结构特征以及宏观胀缩变形与膨胀土微、细观两个结构层次变形间的内在联系；（3）给出了膨胀土宏观胀缩变形的分解机制和描述方法；（4）发展了基于稳定状态的非饱和膨胀土本构模型，编制了可用于膨胀土地基变形计算的有限元程序。. 此外，本项目还开展了相关仪器的研发工作，开发了可测定击实黏性土剪切过程中的渗透特性变化的扭剪试验装置和柱剪试验装置，给出了相应的试验测试方法。相关仪器和测试技术也可应用于含水量变化过程中击实膨胀土的胀缩变形及渗透特性的测量。