花岗岩风化物的湿胀干缩过程与崩岗发生机理研究

Slope collapse is widely distributed in the hilly region of South China. The slope collapse affected area is very large. Its activities and morphological characters are very special and different with the other soil erosion types. Its damages are very serious,which are listed as follow: (1)destroy land resources, (2) damage bridges and roads,(3)deposit river and lake, (4) affect the sustainable development. Thus, slope collapse has become a hotspot in soil erosion field in China. Swell and shrinkage of weathering granite would result in the increase of crack and reduction of shear strength and thus, cause the formation and development of slope collapse. Swell and shrinkage refers to three types of physical and chemical process as follows: (1) thermal expansion or contraction by the difference of temperature between day and night, (2) weathering swell by increase of crack and volume in the weathering process of granite, (3) swell or shrinkage by the physical and chemical reaction between water and hydrophilic minerals. The slope collapse is being controlled in the whole area. The mechanism of slope collapse is needed for revising the measures. Currently more quantilitive studies point out that the infiltration of rainfall and soil water content is the more important factors to affect crack and shear strength of weathering granite while little on the relationships between crack, shear strength and mineral type, soil water content, and the effects of swell-shrinkage on the process of slope collapse. The study site is located in Yudu county, Jiangxi province. In the small catchment deep weathering granite exists and more than 10 slope collapses happen. Here it is the representative slope collapse area. The crust of weathering granite is regared as the objects of the study. The undistributed and distrited soil samples are taken back to the lab. After the treatment, the distributed soil samples is used to analyze the content of hydrophilic minerals and the undistributed soil samples was used for the experiments of the swell or shrinage. The swell/shrinkage ratio,crack and shear strength was measured during the wet and dry process. According the the measurement, the following studies are conducted: (1) the change of swell-shrink, shear strength,crack by water content and hydrophilic minerals is analyzed, (2) the effects of swell-shrinkage by water absorption on crack, shear strength of weathering granite are explored, (3)the mechanism of slope collapse according to the swell-shrink of weathering granite. These provide the technical supports for forecasting and treating slope collapse.

崩岗是南方红壤丘陵区一种特有的侵蚀现象,会对当地的土地资源、生态环境和经济发展构成极大威胁。目前开展的大量研究集中探讨了降雨入渗和土壤含水量对花岗岩风化物裂隙和抗剪强度的影响，但以定性为主，对土壤矿物类型、含水量与土体裂隙、抗剪强度等指标间的定量关系研究不足，也缺乏对湿胀干缩过程引起崩岗发生机理的深入解释。为此，本项目以发育崩岗的花岗岩风化壳为研究对象，通过采集不同层次的原状和非原状土壤样品，测试其矿物组成和进行土体膨胀和收缩控制实验，分析干湿过程中花岗岩风化物胀缩率、裂隙、抗剪强度的变化规律，建立花岗岩风化物的胀缩率、裂隙、抗剪强度与土壤含水量、矿物含量之间的定量关系，探明风化物裂隙和抗剪强度的主要影响因素及其影响程度，以期从花岗岩风化物的物质、结构和力学特性方面揭示崩岗发生的内在机理，为崩岗发生的定量评价提供理论依据。

本项目以江西省于都县左马小流域典型崩岗为研究对象，通过在小流域内典型崩岗剖面上采集原状土和非原状土样品，分析测试了各土层样品中的矿物组成及含量，利用3D构建技术、CT技术等研究了不同土层在吸水和失水过程中的塑性指数、抗剪强度、胀缩率以及裂隙的变化情况，并对4个崩岗在2009-2016年连续开展7次监测，获得了7期DEM数据。主要研究结果如下：崩岗沟头后退的最大速度2.82m/a,崩岗沟的最大年产沙量2389.22t/a；随土壤深度的增加，花岗岩风化土体粘粒、胶粒、石英含量增加，粘土矿物含量减少，塑性指数减小，抗剪强度、粘聚力、裂隙和最大胀缩率增大；在吸水过程中，塑性指数增大，抗剪强度、粘聚力明显减小，裂隙越来越多；而在失水过程中，塑性指数减小，抗剪强度、粘聚力增大，裂隙减小，但当粘聚力不能有效阻滞裂隙的扩展时，裂隙会越来越大，直到土体破裂；抗剪强度与含水量、裂隙与高岭土、胀缩率与蒙脱石相关性最好，其关系表达式分别为Y=-6.62X+403.27，Y=-0.05X+3.26，Y=0.14X-0.92。这些研究结果充分证明了湿胀干缩对花岗岩风化物特性的影响比较大，从而揭示崩岗发生的内在机理，为崩岗预报和制定防治对策提供理论依据。