Dynamic Response Analysis Of Piers Impacted By Debris Flows With Boulders

Debris flows are common geological disasters worldwide,especially in mountainous areas where precipitation is relatively concentrated.Most of the western regions of China meet the basic conditions of topography,material source and water source for the occurrence of debris flows.With the booming economy of the western region and the rapid increasing of traffic demand,more and more bridges have been built in the mountainous areas.Debris flows are serious hazard to bridges and the boulders in debris flows are the main reason for the damage.The current analysis of debris flows impacting piers mostly refers to the impact of pure debris flow slurry or considering the impact of debris flow slurry and boulders separately,which does not reflect the complex interaction among debris flow slurry,boulders and piers.In this thesis,the SPH-FEM coupling method is used to explore the process of the impact of debris flows with boulders on piers and the dynamic response of piers.This thesis first introduces the basic theory of SPH-FEM coupling method for simulating the impact of debris flows with boulders on piers.A numerical simulation model is established based on LS-DYNA.By comparing the results of the numerical simulation and the reference flume test,the applicability of SPH-FEM coupling method to simulate the impact of debris flows on piers is verified.Secondly,based on SPH-FEM coupling method used by the predecessors to simulate debris flows with boulders,different from initializing the debris flow slurry in advance,a new method of generating slurry in the analysis process is used according to the needs.The pier 2# of Liziyida Bridge of Cheng-Kun Railway which was broken during the Liziyida Debris Flow Disaster in 1981 is taken as the background.Based on the post-disaster survey data,the process of the debris flow impacting the pier is analyzed.The influence of the interaction between the debris flow slurry,the boulders and the pier on the dynamic response of debris flows with boulders impacting the pier is explored as well as debris flow velocity,boulders diameter,pier reinforcement and the number of boulders.The results show that the impact of pure debris flow slurry will not cause damage to the pier of Liziyida Bridge and boulders are the main reason to the damage;the process of debris flows with boulders impacting the pier is highly random and the peak impact force on the pier and the peak bending moment at the bottom of the pier have poor correlation with parameters such as debris flow velocity,boulder diameter and pier reinforcement;the peak displacement at the top of the pier increases with the increase of the diameter of the boulder;the duration of the impact of boulders on the pier and the degree of damage of the pier increase with the increase of debris flow velocity and boulders diameter;reinforcement can effectively reduce the damage of debris flows to the pier.