水分迁移作用下压实黄土抗剪强度劣化规律研究

The shear strength will deteriorate gradually under the cyclic variation of the moisture content of compacted loess. Thus, the resulting geological disasters, such as the subsidence, unevenness, longitudinal crack and instability of the loess fill, are serious and inevitable. In this project, basic research would be conducted on the deterioration rules of the shear strength of compacted loess under moisture migration. According to the moisture migration experiments, this project will obtain the expression and the numerical model of total water potential, which consider different affecting factors, and perform the simulation of moisture migration and the calculation of transient moisture field. On the basis of determination of moisture content and the shear strength parameters before and after wetting-drying cycle, the relation between shear strength and moisture content as well as that between shear strength and dry density will be fitted and the deterioration law of the shear strength of compacted loess under cyclic dry-wet process will also be explored. In accordance with the degrading characteristics of compacted loess, the deterioration model of compacted loess (CLDM) will be built. The elastic-plastic analysis method will also be proposed based on the unified strength theory. The research achievements of this project could provide the design and hazard control in loess embankment with the shear deterioration analysis method which is worth considering, and also provide the theory basis for the disaster early-warning and the development of precautionary and reinforcement measures .

压实黄土含水量的周期性变化将导致其抗剪强度逐渐劣化，由此引发的黄土填方体沉陷、波浪、纵裂及失稳等地质灾害问题是十分严峻而又不可回避的。本项目将针对水分迁移作用下压实黄土抗剪强度的劣化规律开展基础性研究。结合水分迁移试验，建立考虑多因素影响的压实黄土总水势表达式及数值模型，实现土体水分迁移过程的模拟与瞬态水分场的计算；通过测定含水量变化及干湿循环后的抗剪强度指标，拟合抗剪强度与含水量及干密度的关系式，探索干湿循环作用下压实黄土抗剪强度劣化规律；根据压实黄土劣化特征，建立劣化模型（CLDM），并基于统一强度理论提出压实黄土劣化弹塑性分析方法。本项目的研究成果可为黄土填方工程的设计、灾害治理提供值得借鉴的强度劣化分析方法，也可为工程的灾变预警、制定防范或加固措施提供理论依据。

近几年，黄土高填方工程在我国西北地区大量出现。我国的西北地区四季分明，降水集中，四季和昼夜的温差较大，降水和温度的变化会使黄土中产生明显的水分迁移运动。水分迁移作用会导致压实黄土内部含水量上下波动即干湿循环，导致压实黄土的强度降低，最终引起工程灾害的发生。本课题从Q3压实黄土水分迁移规律，以及干湿循环对压实黄土造成的强度劣化两方面进行了试验研究。并结合有限元软件二次开发过程，完成了压实黄土边坡稳定性不确定性分析模型。压实黄土水分迁移规律试验研究分为基质势、重力势和温度势三部分。其中基质势试验通过压力板仪完成，分析了6种不同干密度下的压实黄土的基质势变化规律。重力势与温度势试验通过自制试验装置完成，其中重力势试验旨在研究重力影响下6种不同干密度压实黄土的水分迁移的界限含水量，以及重力势作用下土中水分迁移的规律。温度势试验借助冻融循环试验设备，给压实黄土内部制造温度差来研究温度梯度对水分迁移过程的影响规律。针对干湿循环对压实黄土抗剪强度劣化的影响规律，本课题完成了54组不同初始函数量与初始干密度的压实黄土直剪试验，对试验结果进行公式拟合，得出了Q3黄土抗剪强度指标随干密度与含水量变化的经验公式。完成了4种干密度，6种循环次数的UU三轴试验，定量研究了干湿循环造成的压实黄土劣化规律。本课题的研究成果可从一定程度上揭示压实黄土的水分迁移规律以及干湿循环对压实黄土抗剪强度的影响规律，为工程的灾变预警、制定防范或加固措施提供理论依据。