干湿循环效应下胀缩裂隙发育机理及其对崩岗岩土力学特性的影响

Weathering mantle is derived from granite in slope collapse areas, and its mechanical characteristics are influenced significantly under wetting-drying cycles. Swell-shrink crack evolution due to wetting-drying cycle effect results in slope spalling. It is the crux of slope spalling problem to clarify swell-shrink crack evolution under wetting-drying cycles and its effects on mechanical characteristics of slope collapse rock soil. The project aims to examine relationships between water content change, matric suction, swell-shrink crack, swell-shrink deformation and mechanical characteristics of rock soil based on characteristics of weathering mantle derived from granite using in-situ and laboratory tests. With application of image processing technique, the geometric or morphological characteristics of crack patterns are extracted. Swell-shrink crack initiation and propagation are quantitatively described and forecasted for its response mechanism to wetting-drying cycle effects with fractal theory. Artificial neural network model of swell and shrink deformation is established to study and forecast disintegration and shear strength behavior and to clarity evolution mechanism of swell-shrink crack under wetting-drying cycles and its effects on mechanical characteristics of slope collapse rock and soil. Mechanism of slope spalling due to swell-shrink crack under wetting-drying cycle effects is explained not only for contribution to development of slope collapse erosive mechanism, but also for its control and prevention practice.

发育于花岗岩的崩岗风化壳岩土力学特性受水分变化影响显著，而干湿循环效应产生的胀缩裂隙的发生发展往往导致崩岗剥落破坏。因此，阐明胀缩裂隙在干湿循环效应下的发育规律及其对崩岗岩土损伤机理及力学特性，这是揭示崩岗剥落破坏力学机制的关键所在。本项目采用野外原位测试与室内试验相结合的方法，在分析崩岗花岗岩风化壳岩土特性基础上，研究水分变化与基质吸力、胀缩裂隙、胀缩变形、岩土力学特性等关系。采取图像处理技术提取胀缩裂隙几何特征要素，运用分形理论定量描述和预测胀缩裂隙演化规律，从而阐明胀缩裂隙发育对干湿循环效应响应机理；藉此构建胀缩变形的人工神经网络预测模型。预测并研究胀缩裂隙对崩岗岩土抗剪强度和崩解性的影响，揭示胀缩裂隙发育对干湿循环效应响应机理及其对崩岗岩土损伤机理和力学特性影响。阐明干湿循环效应下胀缩裂隙导致崩岗剥落的力学机制，不仅对崩岗侵蚀机理的发展有学术价值，也是科学防治崩岗侵蚀的实践需要。

崩岗发育于花岗岩的风化壳，其岩土力学特性受水分变化影响显著，而干湿循环效应产生的胀缩裂隙的发生发展往往导致崩岗剥落破坏。因此，阐明胀缩裂隙在干湿循环效应下的发育规律及其对崩岗岩土损伤机理及力学特性，这是揭示崩岗剥落破坏力学机制的关键所在。本项目采用野外原位测试与室内试验相结合的方法，从以下三个方面开展研究：（1）崩岗类土质边坡岩土结构特性及其水敏、土力学性能，即分析风化壳剖面岩土结构特性差异：与花岗岩残积土大孔隙比、高压缩性和胀缩性有关的孔隙特征、固结性能和亲水性粘土矿物成分以及下层风化土粒度成分、矿物成分、化学成分、界限含水率、微结构形态以及孔隙特征；基于结构性，对影响花岗岩风化壳岩土崩解、渗透、压缩、胀缩和抗剪性能的诸因素开展野外原位和室内试验的研究和分析；（2）干湿循环效应下胀缩裂隙发育机制，即勘查崩岗流域花岗岩原生节理，调查崩岗边坡地形地貌因子（坡度、坡向、坡型、坡高等），观测由于边坡开挖或坡脚冲淘导致的卸荷裂隙几何特征（走向和倾角、宽度、深度、长度和间距）；研究剖面层次不同干湿阶段、反复干湿循环下土壤水分、基质吸力、体积变化与胀缩特征；确定胀缩裂隙发生的土壤含水率关键阈值；定量描述和预测胀缩裂隙几何特征发展规律；（3）胀缩裂隙演化过程对崩岗岩土力学特性影响，即基于以上研究，分析反复干湿循环下崩岗剖面岩土强度及变形特征；探索土体崩解性和抗剪强度随胀缩裂隙发生发展过程的衰减机制；重要成果如下：（1）明确了崩岗岩土结构特性、水敏、力学等性质；（2）分析了干湿效应下胀缩裂隙发生、发展的影响因素；（3）探索了崩岗岩土随裂隙发展而衰减的规律。研究干湿循环效应下胀缩裂隙导致崩岗剥落的力学机制，不仅对崩岗侵蚀机理的发展有学术价值，也是科学防治崩岗侵蚀的实践需要。