Retention behavior of a flexible barrier in mitigating a granular flow is still an open problem not fully understood, especially due to the complexity of the granular material and the flexible barrier. Understanding the retention mechanism and quantifying the influencing factors of retention efficiency are desirable for optimizing the design and minimizing the maintenance cost of a debris-resisting flexible barrier. In this paper, a numerical model, based on the discrete element method, is presented, calibrated, and validated to analyze the interaction between a granular flow and a flexible net. A fullscale numerical simulation is first performed to compare with a large-scale physical modeling test in the literature and validate the applied parameters in the simulation. The interaction and deposition characteristics of the granular flow interacting with a flexible net are revealed. Afterwards, parametric study is performed to investigate the effects of the internal friction angle (φ) of debris material and the relative mesh size of flexible net on the retention efficiency and clogging mechanism of a flexible barrier. The simulation results illustrate that the particle passing ratio (P) increases with increment of the friction angle of particles and enlargement of the mesh size of a flexible net. Both parameters have critical effects on the retention efficiency of a flexible barrier in intercepting a granular flow. Therefore, the friction angle and the particle size distribution (PSD) characteristics of the debris material are suggested being used for optimization of the mesh size and more efficient design of debris-resisting flexible barriers.
Flexible barriers have been proven to be effective measures for mitigating natural hazards, such as rockfalls, gravel flows and debris flows. This paper presents a new numerical ring model based on the discrete element method (DEM) to simulate a flexible ring net. The Edinburgh Bonded Particle Model is applied to create internal forces within a ring element. The mechanical behavior of a ring element was analyzed from measurements collected during quasi-static tensile tests. The systematic calibration approach of this ring model is described in detail. Two reduction factors related to the bond Young's modulus and the bond radius are proposed to effectively adjust the bending and axial stiffnesses of the ring element. With calibrated DEM parameters from the tensile tests, the ring model is validated by reproducing these tensile tests under different boundary conditions. Finally, a three-dimensional DEM model is established for modeling the rockfall impact on a flexible ring net. A comparison between the existing test data and simulation results reveals that the new ring model can accurately reproduce the response of a flexible ring net under both static and dynamic conditions.
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