卸荷路径下花岗岩残积土力学特性的湿化效应及其微观机理研究

Under the excavation unloading and hot rainy climate, the engineering disasters occurred frequently due to the decay of the mechanical properties of granite residual soil. However, the study on slaking properties of granite residual soil is still not systematically researched and the disaster mechanism is also still indeterminacy. Considering that the granite residual soil has strong features of crack effect, water sensitivity and stress path dependence, this study will conduct the mechanical properties test with different stress paths, where the different control conditions are designed. And the selection and evaluation method of excavation unloading strength parameters will be determined. Then, considering the initial water content, cyclic drying-wetting effect, unloading stress level and other factors, the slaking behavior of soil will be studied under the unloading paths combining with synchronous microscopic test results, the macroscopic mechanical behavior and the evolution process of microstructure of soil will be described, and the performance degradation mechanism of soil will be revealed. On this basis, associating microstructure parameters with mechanical parameters before and after slaking in different initial conditions, perturbation function will be built up. In addition, taking into account of the slaking disturbance, the method of disturbed state model of granite residual soil and its parameters will be determined based on disturbed state concept theory. Based on the results of this study, the performance evolution mechanism of granite residual soil will be elucidated caused by unloading slaking effect in foundation pit engineering, and the understanding of the granite residual soil engineering properties will be deepened as well as the theoretical basis and technical support will be provided for effective prevention on the granite residual soil enrichment area of underground engineering disasters.

开挖卸荷及炎热多雨气候作用下花岗岩残积土力学性状劣化所导致的工程灾害频发，而目前对于卸荷条件下花岗岩残积土湿化特性的研究尚未系统开展，灾变机理尚不明确。本项目针对花岗岩残积土具有较强的裂隙性、水敏性及应力路径依赖性等特征，首先，在不同控制条件下开展多种应力路径下的力学特性试验，探讨基坑卸荷强度参数的选取和评价方法；然后，考虑初始含水率、干湿循环作用及卸荷应力水平等影响因素，进行卸荷路径下土的力学特性湿化效应研究，结合同步微观测试结果阐述土的宏观力学行为及微观结构演变规律，揭示土的性能劣化机理；最后，关联土样湿化前后的微观结构与力学表征参数，基于扰动状态理论，建立扰动函数，提出考虑卸荷湿化扰动的土的扰动状态模型及其参数确定方法。研究成果将有助于深化认识花岗岩残积土的工程特性，阐明卸荷及湿化作用下花岗岩残积土性能的演化机理，为残积土地区基坑工程灾害的有效防治提供理论依据和技术支持。

花岗岩残积土受风化不均影响，其土性具有显著的空间变异性，在天然状态下表现为高液限、大孔隙比的较差物理特性和高强度较优力学特性的异常组合。同时具有遇水湿化、易崩解特性，在有临空面的浸水条件下极易因水的作用而软化崩解，引发工程坍塌等工程灾害。对于明挖法施工及建筑基坑工程中，花岗岩残积土的应力路径不同于室内常规三轴压缩试验中试样，应力状态以卸荷为主。土体卸荷后，微裂隙发展，富水环境更易诱发水流路径通畅、胶结弱化等物理状态改变，宏观表现为土的软化崩解、湿化变形等工程问题。项目以花岗岩残积土基坑开挖卸荷造成侧壁及基底变形为研究背景，结合了基坑工程实际开挖路径和炎热多雨气候的影响，采用土质学与土力学有机结合的方法，深入研究和分析了花岗岩残积土的工程特性；利用三轴湿化试验研究了卸荷路径与湿化效应双重因素影响下花岗岩残积土的力学特性演化规律，分析了卸荷路径下花岗岩残积土在不同初始物理力学条件下的湿化变形和强度特性，结合土的微观结构变化，分析了强度及变形演化规律及微观结构影响机理；关联微观结构参数与宏观力学参数，开展了定量描述花岗岩残积土力学性能的微结构贡献率研究；结合微观结构测试参数开展了相关本构模型研究工作。截止目前，已按项目研究计划完成了所有研究内容，并增加了花岗岩残积土的崩解特性、原位与室内剪切力学性状对比分析、小应变动力参数以及黄泛区河南段粉土力学特性的相关研究内容。揭示了炎热多雨地区基坑开挖及湿化效应诱发基坑变形、坍塌等工程问题的灾变机理，能够为残积土富集地区的基坑工程支护设计与灾害防治提供理论依据和技术支持。