干湿循环作用下压实黄土结构演化机制及其体变时效性

In the engineering practice，intact loess was often compressed to increase the stability of field. However, due to changes of weather or groundwater level etc., loess lies in a dry-wet cycling environment and causes structural evolution of loess mass, furthermore affects the time-dependent effect of compacted loess mass, which it is extremely apt to cause large settlement. In order to reveal the long-term post-construction settlement mechanism of compacted loess from the aspects of soil structure and quantitative prediction, influence of dry-wet cycles on structural evolution mechanism of compacted loess and its time-dependent effect of volumetric change will be studied. First, electrical resistivity method is used to study structural evolution mechanism of compacted loess. The variation law of resistivity of loess samples in the process of dry-wet cycling is obtained and the structural evolution mechanism of loess are analyzed with advanced method, furthermore obtains the structural parameter. Then, the time-dependent effect of volumetric change of loess after dry-wet cycles are studied. The constant rate of strain (CRS) and incremental loading tests of compacted loess with suction control are carried out to obtain the time-dependent volumetric change and the parameters are reliably obtained by comparing these two methods. Finally, the structural parameter and state variable of time-dependent volumetric change are introduced into the yield stress function to construct the constitutive model of compacted loess considering the structure and time-dependent effect, which provides a theoretical basis for prevention and control of the long-term post-construction settlement of compacted loess in the construction of loess areas in China.

工程实践中，经常通过压实原状黄土来增加场地稳定性。然而，由于天气或地下水位变化等原因使黄土处于干湿循环的环境中，致使其结构发生变化，进而影响压实土体的体变时效性，极易引发土体较大的沉降。为了从土体结构和定量预测等方面揭示压实黄土土体长期沉降机制，拟开展干湿循环作用下压实黄土结构演化机制及其体变时效性研究。首先，电阻率法用于压实黄土结构演化机制研究，获取不同干湿循环次数压实黄土的电阻率变化规律，结合先进的分析手段分析黄土结构演化机制，进一步获取结构参数；其次，开展干湿循环后压实黄土的体变时效性研究，通过不同恒定应变速率加载和分级加载方法获取在控制吸力条件下土样压缩体变，对比获取可靠的压实黄土体变时效性参数；最后，将结构参数和体变时效性状态变量引入屈服应力函数，构建考虑结构性与体变时效性的压实黄土本构模型，为我国黄土地区建设中长期工后沉降的预防和控制提供理论依据。

压实黄土常作为工程填料，易受到环境中降水和蒸发等干湿循环作用，影响土体结构变化及体变时效性。为此，本项目开展了电阻率特征等相关测试仪器和方法的开发，干湿循环作用下压实黄土细观结构演化特征，以及基于分级加载和恒应变速率方法压实黄土压缩变形特征等研究。本项目研究结论为：（1）通过改造已有的压力室，开发了可测量试样电阻率的压力室，可用于表征压实黄土变形过程中的结构特征变化。另外，提出了三维权重理论和相关数值方法，以计算时域反射探针的空间灵敏度。通过组合探头和三针探头等试验和计算数据的对比，验证了此理论方法的合理性。（2）恒应变速率方法可较快获取压实黄土的连续压缩变形曲线点。随着平均含水量增大，弹性和塑性指数先增大，而在平均含水量最大时减小。随着竖向应变增大，较低含水量压实黄土平均结构因子和平均形状因子减小，而最大含水量的则增大，各向异性指数先减小后稍微增大。随含水量增大，平均结构因子和平均形状因子减小，各向异性指数则先减小后增大。（3）压实黄土的电阻率和裂隙比随干湿循环次数的增加而增大，裂隙比增大引起电阻率增大。另外，干湿循环后，较低密度饱和压实黄土塑性压缩指数减小，屈服应力增大，而较高密度饱和压实黄土呈相反趋势。（4）分级加载和恒应变速率压缩过程中，导致压实黄土失水速率较快的恒应变速率压缩变形曲线变形量大于分级加载获取的曲线。（5）提出了考虑裂隙影响的电阻率计算公式，并验证了公式的合理性。