花岗岩风化土体微形态特征及其与崩岗发育的关系

Weathered granite soil is widely distributed in southern China, on which have had a serious collapsing gully erosion. The micromorphological features can reflect the properties of granite weathered soil, providing an important way to understand the development mechanism of the collapsing gully. This project will investigate the micromorphological features of granite weathered soil and discuss its relationship with the development of collapsing gully. The granite weathering soil in the southeast of Hubei Province will be used as the research subject. The overall idea is developed as "soil micromorphological features → relationship with the geotechnical mechanics feature → collapsing gully development mechanism". Combining with microscopic observation and theoretical analysis, the soil profile characteristics, composition and its alteration with the weathering layers are determined by using a regular survey and analysis methods. The micromorphological features of different weathered layers and their alteration with the weathered layers will be revealed by analyzing the soil matrix, skeleton grains, microstructure types and pore characteristics using a combination of soil slice preparation and photomicrography, and the three-dimensional simulation of pore properties will be analyzed. The geotechnical mechanics feature is tested and the slide of collapsing gully wall is observed along with the development process of collapsing gully and then to determine its relationship with soil micromorphology. From the perspective of the soil micromorphological features, this project illustrates the essential cause of the development of collapsing gully, and provides a new theoretical basis and support to reveal the development mechanism of collapsing gully in the granite area.

花岗岩风化土广泛分布于我国南方地区，并在其上产生了严重的崩岗侵蚀，土体微形态特征能够反映出花岗岩风化土的本质属性，因此也是深入认识崩岗发育机理的重要途径。本项目以鄂东南花岗岩风化土为研究对象，按照“土体微形态特征→与土体岩土力学特性关系→崩岗发育机理”的整体思路，采用微观结构观察与理论分析相结合的方法，开展花岗岩风化土微形态特征研究并探讨其与崩岗发育的关系。利用常规调查与分析方法，明确土体的剖面特征、物质组成及其随风化层次的变化规律；结合土壤薄片制备和显微摄影技术，分析土体的基质、粗骨颗粒、微结构类型以及孔隙特征，开展孔隙特征的三维模拟，揭示不同风化层次的微形态特征及其随风化层次的变化规律；分析土体的岩土力学特性并结合崩岗发育过程中的崩壁崩塌等观测结果，揭示其与土体微形态特征的关系，从土体微形态特征的角度阐明崩岗发育的本因。从而，为花岗岩区崩岗发育机理的揭示提供新的理论依据和支撑。

花岗岩风化土广泛分布华南地区，其上产生了严重的崩岗侵蚀。崩壁是崩岗演变中最活跃的部分，崩岗的发展主要是通过崩壁的坍塌来完成。土体微形态特征能够反映出花岗岩风化土的本质属性，同时含水量和坡度是反映崩壁稳定程度的重要指标，因此也是深入认识崩岗发育机理的重要途径。本研究以通城县典型的崩岗崩壁不同风化层次的土体为研究对象，按照表土层（TC1）、红土层（TC2、TC3、TC4）、砂土层（TC5、TC6）划分为不同土层。依托土壤微形态学的理论与研究方法，分析其崩壁土体特性随土层的变化规律，探明崩岗不同土层土体微形态特征空间分异规律。采用ABAQUS软件，从坡度、土壤水分含量及龛的演变的角度定量探讨了崩壁的稳定性。结果表明：（1）各土层观察发现土层颜色随着深度的增加颜色呈现暗红色至浅红色和灰白色，表明含有氧化铁、锰的胶结物质逐渐减少。（2）随着土层加深，土壤中矿物颗粒逐渐增大，粗骨颗粒的含量也明显增加，但粗骨颗粒的数量先增加后减小。（3）除表土层外，土壤孔隙普遍发育不好，孔隙类型总体上以囊孔和裂隙为主，部分孔道中有呈带状的有机颗粒，可能是有机物质顺着水流在孔隙中分布。（4）通过主成分分析筛选出7个指标（土壤基质颜色、土壤基质类型、土壤基质比、土壤团聚体、土壤结构体、总孔隙百分比和有机质含量）作为最小数据集对崩壁土体进行稳定性综合评价，两种评价结果相关性显著，并且综合评价的结果与崩壁各层次崩解特性和抗剪特性相关性显著。（5）龛深与安全系数服从线性负相关函数关系；红土层的含水量是引起崩塌的最重要因子，坡度对崩壁稳定性影响较大，龛高相对砂土层厚度的比例及崩壁高度对崩壁的稳定性影响极小。龛深与红土层的临界饱和度之间的负相关性可用二次多项式表达。开展崩壁的微形态特征研究，弄清土体的微形态特征随土层的变化规律及其与崩岗发育的关系，增加了对崩壁的微观尺度上的认识，为监测崩岗的发育提供较好的方法，对崩岗治理具有重要的现实指导意义。