Experimental and numerical study of dynamic soil debris impact load on reinforced concrete debris-resisting barriers

Abstract

In Hong Kong, design practice adopts the hydrodynamic load model to estimate the dynamic soil debris impact load on reinforced concrete debris-resisting barriers. A dynamic coefficient of 2.5 is empirically adopted, which takes into account the effect of the impact of boulders up to 0.5 m in diameter. With a view to rationalising the design of reinforced concrete debris-resisting barriers, the Geotechnical Engineering Office (GEO), in collaboration with the Hong Kong University of Science and Technology (HKUST), initiated a study to investigate the dynamic impact of soil debris. In particular, a series of large-scale impact tests using 4 m3 realistic debris mix and a 1.8-m-high reinforced concrete model barrier were conducted in the flume facility in the Kadoorie Centre in Hong Kong. The tests were well controlled, and the flow kinematics, including flow depth and flow speed, and the time history of the impact load at the wall stem subject to the debris impact were measured, which provided critical test data on assessment of the hydrodynamic load of soil debris hitting reinforced concrete structures. The scale of these physical impact tests under such a controlled environment was unique as compared with other studies in the literature. To further examine the dynamic impact force, a calibrated numerical model using a three-dimensional finite-element computer package, namely LS-DYNA, was adopted to simulate the impact scenario for a real-scale debris flow event of 400 m3, where an arbitrary Lagrangian-Eulerian technique was adopted to simulate debris materials. Based on both the experiments and numerical analyses, debris run-up along the wall stem was observed when the debris hit the model barriers. Under the experimental setting, the hydrodynamic soil debris pressure coefficients were consistently found close to unity, which are generally in line with that used in overseas technical guidelines or design practice. This study enhances fundamental understanding of the soil debris impact mechanism on reinforced concrete barriers and provides scientific evidence to rationalise the design guidelines used in Hong Kong.