Numerical Simulation Study Of Water-related Landslide Movement And Surge Hazard

Landslides are the most hazardous geological hazards in China,and the separately impacted water bodies after the collapse of water-related landslides will produce secondary disasters of surge waves,causing serious threats to people as well as building safety.In order to achieve accurate simulation of landslide waves,worldwide academicians have made a series of achievements in numerical simulation methods.However,most of them focus on wave theory,ignoring the process of landslide movement,while detailed description of landslide movement characteristics is necessary to ensure the accuracy of subsequent wave simulation results.In addition,at present,domestic related research mostly focuses on the analysis of the wave generation and propagation process of landslide surges in the reservoir area,and the analysis of the propagation law of tsunami waves induced by large-scale landslides is less.In view of the above research status,this paper based on the actual problem,according to the different generalization methods to establish rigid body slip landslide dynamics model and mobility slip landslide dynamics model.The COMCOT program,which was originally used for large-scale tsunami simulations,is extended for the simulation of landslides and surges on banks with narrow boundaries,and a numerical method is proposed that is computationally efficient,accurate and applicable to the simulation of wading landslides and surges at different scales.The main research elements are as follows:(1)According to the different generalization methods of landslide dynamics models,the calculation methods of landslide motion velocity for rigid body slip models and fluidity slip models are proposed.For the rigid body landslide model,the FORTRAN computer language is used to program the simulation method for the motion velocity of submarine landslide and reservoir bank landslide,and the difference in geotechnical capacity and friction is considered for the different water-related conditions of the geotechnical body.For the fluidity landslide model,the liquefaction of the soil in the slip zone due to pore water pressure under the action of earthquake and rainfall is considered,and the characterized friction angle is introduced to describe the slope slip damage caused by liquefaction,and the difference in friction is considered.The two models are analyzed with regard to the assumptions on the force conditions of the landslide bars,the establishment of the equilibrium equations of the force system,the composition of the water resistance of the wading landslide during underwater movement,the parameters taken into account in the analysis method,and the secondary development and data processing of the mobility slip model based on VBA and FORTRAN computer language,laying the foundation for the subsequent simulation of surges in combination with the COMCOT program.(2)Taking the Aleutian tsunami that occurred in 1946 as an example,both rigid body slip and fluidity slip landslide dynamics models are used to simulate and restore the motion process of submarine landslide.Combined with the submarine landslide module in COMCOT Tsunami model developed by Cornell University as the trigger mechanism of tsunami,the generation and propagation of tsunami and the climbing process along the coast are comprehensively discussed and analyzed.The simulation results of tsunami wave under different landslide motion calculation methods and tsunami climbing at the Scotch Cap lighthouse on Unimak Island are compared and analyzed.The results show that in the numerical calculation,the difference of the landslide movement mode will affect the simulation study of the subsequent surge.Because the submarine landslide is immersed in water for a long time,the cohesion and shear strength of the rock and soil are low,and the dynamic model of the mobile landslide can well reflect its motion characteristics.The swell simulation prediction results of the sexual slip model are more accurate and more conservative at the same time.(3)Using the Gongjiafang landslide surge in Three Gorges reservoir area as an example,the movement velocity calculation method of landslide rigid body slip as well as fluidity slip is used to simulate the whole process of Gongjiafang landslide movement considering the parameter difference between above and below water geotechnical body.The COMCOT tsunami model is extended from surface tsunami simulation to the application of surge simulation in the reservoir bank channel.According to the simulation results,the propagation pattern of surge waves in the river cross-section,the propagation pattern at different moments and the height of climbing waves along the final canyon are analyzed,and different evaluation indexes are selected to compare the tsunami simulation effects of two landslide dynamics models.The results show that the leading edge of the Gongjiafang landslide is affected by the hollowing effect of the fluctuating reservoir water level and is less stable,and the landslide presents graded and segmented progressive damage,and the coupled numerical simulation method of fluidity landslide surge is practically feasible for the reservoir bank landslide surge,which is more efficient and accurate than the rigid body slip model for the simulation of surge.(4)The derived surge model of the fluidity slip dynamics model is introduced to simulate the motion velocity of the Aleutian submarine landslide as well as the Gongjiafang landslide.Specifically,this model is used as the premise of surge triggering and input to the fluidity motion model to visualize the tsunami triggered by the submarine landslide as well as the surge induced by the reservoir bank landslide for three-dimensional simulation and to compare the calculation results with the COMCOT model horizontally.The results show that this derived surge model has a high degree of connectivity and convenience,but the simulation effect is generally small as it simplifies the movement of the water body.The COMCOT model-based coupled mobility landslide surge simulation method has shown higher accuracy and applicability for both submarine landslide tsunami and reservoir bank landslide surge simulation studies.