Numerical Simulation Of Landslide Surge In Fracturable Rock Mass Based On Coupled FDEM-CEL Method

In southwest China,there are many alpine canyons,and the terrain and geological conditions are complex.At the same time,many hydraulic structures such as dams and hydropower stations are distributed on the main roads of major rivers,making the reservoir area have a huge potential risk of landslide surge disaster.Once a landslide event occurs in the reservoir area,the resulting surge will damage the hydraulic structures in the reservoir area and destroy the ecological environment around the reservoir area.More seriously,once the dam breaks or overflows,it not only brings huge economic losses,but also threatens the life safety of the staff in the reservoir area and the residents in the surrounding villages and towns.Therefore,it is of great practical significance to carry out research on landslide surge in reservoir area,which can provide theoretical support and scientific basis for disaster prevention and mitigation.Based on the ABAQUS simulation platform,a two-dimensional numerical model of landslide surge is established.The numerical method of coupled finite-discrete element method(FDEM)and Euler-Lagrange method(CEL)is used to simulate the landslide surge process of fractured rock mass.The effects of tensile strength and friction coefficient of rock mass on the velocity and kinetic energy of landslide mass,surge height and surge climbing height are studied.Secondly,a three-dimensional landslide surge model is established on the basis of the two-dimensional model.The process of landslide surge in fractured rock mass under different water depth conditions is discussed.The evolution characteristics of landslide morphology and kinetic energy,the evolution characteristics of surge morphology in cross section and longitudinal section of river channel,the evolution characteristics of surge height,the evolution characteristics of surge height on the opposite bank and the evolution characteristics of surge height in front of dam are analyzed.The main research results are as follows:(1)In general,when the friction coefficient is the same,the greater the tensile strength,the smaller the degree of fragmentation of the landslide during the movement,the greater the water entry speed and kinetic energy,the greater the maximum wave height and climbing height of the surge;when the tensile strength of rock mass is the same,the greater the friction coefficient,the greater the degree of fragmentation when the landslide slides,the smaller the water entry speed and kinetic energy,and the smaller the maximum wave height and climbing height of the surge.(2)In the case of different combinations of tensile strength and friction coefficient of rock mass,there may be a special case of landslide body entering water in stages.It should be noted that if the primary surge is impacted and squeezed again by the sliding rock mass when it flows backward,it will lead to a larger maximum climbing height of the surge on the opposite bank.(3)In the early stage of the three-dimensional landslide,the front rock mass detects the inclined slope surface,the middle landslide body begins to produce cracks,and the trailing edge settles and the depression area appears.After the landslide slides down,it continues to break and disintegrate.The side rock mass diffuses to both sides without lateral constraints,forming a flat-long loose accumulation body.The front rock mass is protruding in the middle,and the two sides are slightly backward.The tongue begins to wedge into the reservoir channel.(4)The propagation characteristics of landslide surge under different water depth conditions are different.The smaller the water depth is,the longer the acceleration time of the landslide is,the larger the water entry velocity and peak velocity are,and the larger the maximum surge height is.In general,the higher the height of the surge,the higher the surge will lead to higher surge climbing.There are also special cases,such as the backflow of water near the landslide impact pit,which may lead to smaller surge height but larger surge climbing height.(5)Based on the evolution process of surge in the cross section and longitudinal section of the reservoir area,it is found that the smaller the water depth,the more violent the change of surge,especially in the area directly in front of the landslide center.The landslide body squeezes and replaces the water body to produce extremely steep surge.(6)The surge propagates to the downstream in an arc shape.The surge climbs first at the center of the dam,followed by the left abutment,and finally the right abutment,but the surge climbs at the right abutment.In addition,when the water depth of the reservoir area is small,the evolution process of surge climbing at different positions of the dam shows obvious similarity.With the increase of water depth,the period of swell run-up at different positions in front of the dam is deviated,and the peak of swell runup is also different.