台风暴雨矿渣型泥石流形成机制与动力特征——以兴宁乌石坑沟泥石流为例

Formation mechanism and dynamic characteristics ofmine-slag debris flow in typhoon rainstorm---Take Wushikeng gully in Xingning as an example

受台风“尤特”登陆影响,台风暴雨直接激发兴宁乌石坑沟特大矿渣型泥石流灾害,物源巨大,潜在危害极大。笔者等通过现场调绘及室内试验,对本次泥石流的形成机制及动力特征进行研究,旨在为此类泥石流致灾机理及危害性评价提供借鉴。研究表明,其独特的流域地形特点为泥石流形成的基本因素,以沟道堆积物为主的丰富矿渣型物源是基础条件,高强度的台风暴雨是直接激发因素,与矿山开采、矿渣随意堆放等人为因素共同作用扩大了灾害规模。泥石流形成过程与动力特征为前期强降雨—崩滑碎屑流—矿渣型泥石流—台风暴雨—沟道堵塞雍高—溃决、规模放大。

Objectives: Typhoon rainstorm is an important rainfall type that induces geological disasters in the coastalareas of South China. Affected by the landfall of typhoon “Utor”, the typhoon rain directly triggered the extralargeslag-type debris flow disaster in Wushikeng Gully in Xingning, which caused huge material sources and greatpotential harm. At present, the research on the slag debris flow in typhoon and rainstorm is still at the initial stage,mainly focusing on its formation mechanism, disaster characteristics and other aspects. There are problems such asnarrow research scope, single method and few achievements. Therefore, it is of great significance to study theformation mechanism and dynamic characteristics of the slag debris flow in typhoon and rainstorm for the disastermechanism and hazard evaluation of such debris flow.Methods: We collected, sorted and analyzed the geological environment background. The Wushikeng Valleyin Xingning is a typical typhoon-rainstorm-landslide-debris flow disaster chain area, which is a high incidencearea of debris flow. The volume and physical and mechanical parameters of the material source were exploredthrough measurement, drilling, density and particle grading in-situ tests and laboratory tests. The channel depositsaccounted for 81. 9% of the total material source. In combination with the material composition and deformation anddamage characteristics of the slag pile, the stability of the slag pile was calculated and evaluated by the slicemethod. We collected and analyzed the rainfall data during the typhoon period. The rainfall and rainfall intensity exceeded the critical rainfall index for triggering debris flow in the region. Calculated the dynamic characteristicparameters of debris flow such as flow velocity, flow rate and fluid impact force and their change rules, furtheranalyzed the characteristics of debris flow movement and accumulation process, and quantitatively analyze andevaluate the debris flow activity trend from the aspects of debris flow activity duration, rainstorm intensity index andrisk assessment.Results: The formation mechanism of slag type debris flow in typhoon rainstorm: its unique watershedtopographic characteristics are the basic factors for the formation of debris flow, the rich slag type material sourcemainly composed of channel deposits is the basic condition, the high intensity typhoon rainstorm is the direct triggerfactor, and the joint action of mine mining, random stacking of slag and other factors has expanded the disasterscale. The formation process and dynamic characteristics are summarized as follows: early heavy rainfall-landslidedebris flow-slag debris flow-typhoon rainstorm-channel blocked and highed-collapse and scale enlargement. Thecomprehensive debris flow has a strong rainstorm index R = 6. 41, occurrence probability of 0. 2~0. 8 and hazarddegree H of 0. 6260. The debris flow is in the youth stage and belongs to highly dangerous debris flow. Typhoonand rainstorm often occur in this basin, and it is very likely that large-scale debris flow will break out again. Itsharm and impact range is larger. Therefore, the prevention and control of debris flow should be studied.Conclusions: This paper takes the debris flow in Wushikeng Gully in Xingning as an example, takes thegeological environment of debris flow as the research background, studies the formation conditions and mechanismof debris flow, and studies the dynamic process characteristics of the slag debris flow in typhoon rainstorm throughtheoretical calculation. Typhoons and rainstorms occur from time to time in the basin, and it is very likely that large-scale debris flows will erupt again, therefore research on the prevention and control of debris flow should becarried out, which provides a reference for the disaster mechanism of such debris flow and the prevention andmitigation work in similar disasters.