Coupled numerical simulation of a flexible barrier impacted by debris flow with boulders in front
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L. Zhao I J. W. He I Z. X. Yu I Y. P. Liu I Z. H. Zhou I S. L. Chan
Coupled numerical simulation of a flexible barrier impacted by debris flow with boulders in front
Abstract Flexible barriers have been widely adopted to mitigate the debris flow disasters. However, the research on the coupled interaction analysis between flexible barriers and debris flows with boulders in front is rarely reported. In this paper, a two-stage coupled modeling technique which can account for the debris mobility, the non-linear behavior of a flexible barrier, and the dynamic interaction between flexible barriers and debris flows is developed firstly based on the Arbitrary Lagrangian-Eulerian (ALE) method using LS-DYNA. The proposed coupling model is verified by a large-scale field test, comparing the flow velocity and flow depth of the debris flow, as well as the internal force and deformation of the flexible barrier. Further, the proposed numerical model is adopted to study the performance of flexible barrier impacted by debris flow with boulders in front. Two practical cases that the debris flow contains a single boulder with a diameter of 2 m and 1 m in front, respectively, are investigated. The impact positions are both the bottom center of the middle functional module of the barrier. The numerical results show that the barrier cannot intercept the debris flow with a boulder of 2 m in diameter. When the flexible barrier is subjected to three 1 m boulders in front of the debris flow, plastic hinges are formed at impact positions of the steel posts. It is recommended that additional protection measurements are required to maintain the structural integrity. Keywords Flexible barrier . Debris flow . Front boulder . Coupled numerical simulation . Design recommendations Introduction Natural hazards such as debris flows and rockfalls usually occur within natural terrain areas. Such incidents become severe threats to railways and highways built in the mountainous areas. Since the development of urbanization in many cities, such as Hong Kong, hilly terrain is always involved in the residential area. The hazards would also create safety risks to residential houses and human lives. Flexible barrier is one type of mitigation structures commonly applied at slopes to resist falling rocks and debris flows. Different from rigid structures like embankments and rock galleries made from reinforced ground and concrete, flexible barrier consists of four major steel components: steel posts, wire nets, cable ropes, and brake elements. This flexible steel fence system is capable to intercept falling rocks and debris flows (Fig. 1) benefitting from its highly nonlinear and large deflection behavior; it would undergo large elasto-plastic deformation and dissipate energies when subjected to impacts. In recent years, three main approaches namely field investigation, large-scale test, and numerical simulation have been adopted to study the performance of flexible barriers under the impacts of debris flows. The actual performance of flexible barriers under the
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