崩岗侵蚀区崩壁土体湿化机理及影响因素分析

Analysis of Soil Wetting Mechanism and Influencing Factors on the Headwall of Collapsing Hill and Erosional Gully

以广东五华县莲塘岗崩岗崩壁土体为研究对象,结合土体物理特性,采用野外湿化试验测定土体浸水后的完全崩解时间,初步阐明其湿化机理,并分析其影响因素。结果表明:(1)崩壁不同层位土体的成份、结构、粒度等存在差异,使其物理性质受水力作用影响显著,抗冲抗蚀能力从强到弱分别为表土层、红土层、砂土层。(2)崩壁不同层位土体浸水后,水呈非均衡态进入土体孔隙,粒间斥力超过吸力,产生应力集中现象,使土体结构受到破坏,导致崩解现象发生;砂土层崩解速度明显高于表土层和红土层,遇水软化性极强。(3)土体结构的粒度成分及孔隙性影响崩壁土体的崩解性。相比红土层和表土层,砂土层粗颗粒含量较高,湿化崩解时间较短。孔隙发育程度较低的红土层,其湿化崩解所需时间比砂土层长;从红土层到砂土层,随着初始含水率增大,崩解速度不断加快,意味着红土层受到水力侵蚀后,下部砂土层受到的侵蚀将更加严重。一旦水分下渗至砂土层,将导致崩岗侵蚀进一步快速发展。

The study selected the soils of headwall in Liantanggang collapsing hill and erosional gully in Wuhua County of Guangdong province as the research object. Based on soil physical properties, the wetting test method was performed to measure the complete disintegrating time after the soils had been soaked in water. The wetting mechanism was preliminarily clarified and the influence factors were analyzed. The main results showed that： （1） The composition, structure, and particle size of soils in different positions of headwall were different, leading to significant hydraulic effect on soil physical properties. The ability to resist erosion decreased in the order of surface soil layer, red soil layer, and sandy soil layer. （2） After the soils in different positions of headwall were soaked in water, the water entered soil porosity by disequilibrium state. The interparticle repulsion was greater than the suction and the soil structure was damaged by the concentration of stress, leading to the disintegrating phenomenon. The disintegrating speed of sandy soil layer was significantly higher than those of the surface soil layer and the red soil layer, and the water softening of sandy soil layer was strong. （3） The particle size and porosity of soil could influence the disintegration of the headwall soil. Compared with the red soil layer and the surface soil layer, the sandy soil layer had more coarse particle content, leading to shorter disintegrating time of wetting. The development degree of porosity of soils in red soil layer was lower, resulting in longer disintegrating time of wetting than the sandy soil layer. The disintegrating speed accelerated with the increasing initial moisture content from red soil layer to the sandy layer, indicating that the erosion of sandy soiI layer would be more serious after the red soil layer had been suffered water erosion. Once the water infiltration reached the sandy soil layer, it could lead to the further rapid development of erosion of collapsing hill and erosional gully.