干湿循环作用下非饱和膨胀土持水和力学特性与其耦合本构模型

Expansive soils exist in many regions of China, and it is sensitive to the climate change. Geological or engineering disaster often ocurrs due to drying and wetting cycles in the area of expansive soils. Volume expansion and contraction due to wetting and drying are important issues of unsaturated expansive soils and also are important characteristics different from other unsaturated soils. To study water-retention behaviour and mechanical behaviour including volume expansion and contraction during drying and wetting process and their constitutive modelling is a fundmental issue for understanting and predicting various kinds of the disaster and proposing the control measure. On the basis of the existing research results of unsaturated expansive soils, a series of experimental study on the water-retention behaviour and mechanical behaviour of expansive soils and their coupling is planned by using the suction-controllable or measurable oedemeter and triaxial testing apparatus for unsaturated soils,the vapour equilibrium method and the filter paper method, and taking one kind of typical expansive soil in China as a testing material. On the basis of the hydromechanical coupled elastoplastic constitutive model proposed by the applictant et al. for predicting the water-retention behaviour and mechanical behaviour of unsaturated expansive soils, to develop a new coupled model is planned, which can describe the water retention behaviour and mechanical behaviour of expansive soils with the drying and wetting cycle effect and ever-experienced suction effect being into consideration. In the modelling, the drying and wetting circle effect and ever-experienced suction effect are taken account by using the bounding surface method proposed by Dafalias et al. and imitating the elastoplastic model by Yao et al. for modeling of overconsolidated clay behaviour, respectively. This project can provide some useful research results for geotechnical engineering problem with unsaturated expansive soils.

我国多地存在非饱和膨胀土。对气候变化敏感的膨胀土，经常因干湿循环引起地质或工程灾害。吸水膨胀和脱水收缩是膨胀土的重要特性，也是区别其他非饱和土的重要特征。研究非饱和膨胀土在干湿循环过程中的持水特性和包括湿胀干缩在内的力学特性及其本构模拟是理解和预测膨胀土的各种灾害和提出防止措施的基础。本项目计划在已有研究成果的基础上，以国内典型的膨胀土为试验材料，利用可控制吸力或量测吸力的非饱和土固结仪和非饱和土三轴仪，以及蒸汽平衡法和滤纸法，在干湿循环条件下对膨胀性土进行持水特性和力学特性及其两者耦合性质的试验研究。在申请人等已提出的膨胀性非饱和土的持水-力学性质耦合的弹塑性模型基础上，考虑干湿循环滞回效应和胀缩性，采用边界面理论和建立超固结黏土本构模型所用的手法，建立能够反映干湿循环滞回效应和吸力作用历史效应的持水-力学性质耦合的弹塑性本构模型。本项目可为膨胀土相关的岩土工程问题提供有用的研究成果。

以膨胀性土为主要试验材料，在各种吸力/应力路径下研究非饱和膨胀性土的持水和力学特性及其本构模拟。主要成果如下。.1）全吸力范围内膨胀性土的土水特征曲线.用压力板法、滤纸法和饱和盐溶液蒸汽平衡法，对南阳膨胀土、淮安膨胀土和桂林红粘土进行了土水特性试验，得到全吸力范围内土水特性和变形特性。.2）干湿循环下膨胀性土的持水和变形特性.对经过不同次数饱和与烘干干湿循环的压实高庙子钙基膨润土和南阳膨胀土进行饱和盐溶液蒸汽平衡法的土水特性测试，研究了不同干湿循环次数对其土水特性的影响；对每一次脱湿后试样表面拍摄照片并进行图像处理，得到了不同干湿循环次数下收缩变形和裂隙开展的影响规律。.3）多次干湿循环后土水特征曲线的模拟.结合已有的试验数据，总结整理脱湿曲线与吸湿曲线随着干湿循环次数的变化规律，通过引入一个与干湿循环次数的函数，提出能预测多次干湿循环后土水特征曲线的方法。.4）吸力历史对土水特性和力学特性的影响.对受过不同吸力历史的非膨胀性土（珍珠土）和膨胀性土（南阳膨胀土）样进行一系列的吸力控制的三轴试验，揭示了吸力历史对非饱和土的土水和力学特性的影响规律，为研究多次干湿循环对非饱和土的水力和力学特性的影响规律奠定基础。.5）非饱和膨胀土的浸水变形特性及其预测.用两种非饱和弱膨胀土（淮安膨胀土和桂林红粘土）进行K0应力条件下浸水变形试验，得到了浸水引起的弱膨胀土的变形特性，给出非饱和膨胀土的浸水饱和变形的预测方法。.6）盐溶液下高庙子膨润土的力学特性及其预测.对两种高庙子钠基膨润土，在不同密度和应力下进行纯水和盐溶液饱和下的膨胀变形特性以及强度特性试验，提出了对我国核废料处置库设计有用的盐溶液饱和膨胀变形和膨胀力预测方法。.7）土结构性对土水和力学特性的影响.对三种土结构的土样（原状土、击实或压实土、泥浆予固结土）进行土水特性和力学试验，研究土结构性对非饱和土持水和力学特性的影响。