华南花岗岩红壤区崩壁裂隙发育对崩壁稳定性的影响

The collapsing hill is a specific form of soil erosion in the granite red soil region of Southern China，especially in Guangdong province．It is one of the most important indications of serious soil erosion. The area of collapsing hill is 8,3500 ha.in Guangdong province,accounting for 67.83% of total collapsing hill area in China.It is proved that serious collapsing hill has been destroying the physical environment and threatening the socio-economic development in Guangdong province.As the material source of collapsing hill, the collapse of collapsed walls is the most active part of collapsing erosion. The development of soil cracks in collapsed walls increases the permeability and demages the strength of cemental soil,providing channels for rainfall infiltration and water evaporation,which triggers collapsing wall erosion and accelerates the collapse of collapsed walls. In the past，research method on collapsing hill is relatively simple and limited，with a narrow perspective，and research topics are too broad and lack details．Because of these limitations,we plans to use a combination of plot-based detailed representation and laboratory experiment based on broad fiel investigation to study the soil permeability and its change with water content,the strength of cemental soil and it change with soil moisture and the water infiltration time,the stress of soil in collapsed walls under different extent of soil cracks development in collapsed walls with given rainfall infiltration conditions. Furtherly, we tries to describe quantitatively the impact of soil cracks development on the stability of collapsed walls and the unsteady sediment. This study aims to improve the understanding of physical mechanisms of collapsing hill erosion and policy enlightenments for comprehensive control of collapsing hill erosion.

崩岗是华南花岗岩红壤区特殊的水土流失形式，而广东崩岗隐患最为突出，广东省崩岗面积8.35万公顷，占全国崩岗总面积的67.83%。崩岗的大面积发育，对广东自然环境和社会经济发展造成了极大破坏。崩壁的崩塌是整个崩岗演变过程中最活跃的部分,也是崩岗运动的物质来源，而目前关于崩岗崩壁侵蚀的研究不深入和系统。崩壁裂隙发育增强了土体的渗透性并导致其强度降低，为降雨入渗和水分蒸发提供了通道，是崩壁侵蚀启动和加速崩壁坍塌的一个重要过程。 本项目拟通过面上调查，野外试验研究和室内试验，从崩壁裂隙发育入手，研究裂隙不同发育程度土体在一定降雨入渗条件下土体渗透特性及其随含水量变化的规律，土体的强度特性及随土壤水分变化和入渗时间变化的规律，分析崩壁土体的受力情况,定量评价裂隙发育对崩壁稳定性、崩塌堆积量的影响。为深入阐明崩岗侵蚀的成因机理，进一步丰富崩岗侵蚀理论和采取有效的防治措施提供科学依据

本项目针对崩岗地貌发育过程中崩壁裂隙发育对崩壁的稳定性来探究崩岗侵蚀机理，本项目以广东德庆马圩镇深涌水土保持监测站为研究基地，四年中不断调查研究区域的崩岗地貌发育情况，进行了研究区的植被状况、土壤类型、裂隙发育等面上调查，选择一个活动型崩岗进行了原位定点崩壁裂隙发育观测、崩壁土体理化性质测试、室内裂隙发育过程模拟、崩壁土体渗透性、崩解特性、土体强度特性等的综合试验研究，结合定位点的气象数据和无人机监测崩岗地貌发育过程，获得了第一手的野外调查数据和资料。主要研究结果如下：（1）崩岗与裂隙息息相关，裂隙成为了边坡崩塌和直接产生重力侵蚀的重要因子，崩岗发育完全受裂隙所控制，华南花岗岩风化壳裂隙是崩岗侵蚀所特有的成因之一；（2）崩壁不同部位土体裂隙发育程度达到相对稳定时的土壤含水量和时间不同，其中崩壁顶部（B1）土体最先产生裂隙和达到稳定状态，其次是中部（B2），最后是下部（B3）；由于崩壁土体裂隙的发育程度不一，在到达稳定的时间和含水量的不同，从而导致崩壁土体各部位受力不均，土体强度产生差异，从而最终导致在雨季崩壁失稳而发生崩岗。（3）崩壁土壤水分对土体强度的影响显著，当土壤含水率在15%时，对应的黏聚力c和内摩擦角φ指标均出现峰值；黏聚力c指标变化幅度较大，随着土壤水分的增加呈现先增大后减少的趋势，而内摩擦角φ处于一直衰减状态。（4）在崩壁土体垂直剖面上，碎石角砾残积层的崩解速度最快，红土层最慢，崩解速度快慢表现为：红土层<砂土层<碎屑层<碎石角砾残积层；初始含水量对红土层、砂土层的崩解速度影响较大，对碎屑层、碎石角砾残积层的影响较少。影响崩壁土体崩解特性的理化因子众多;(5)初步建立了崩壁失稳的数学模型，但有待进一步的监测数据验证。