Experimental investigation on the impact force of the dry granular flow against a flexible barrier
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Xiao Siyou I Su Lijun I Jiang Yuanjun I Qu Xin I Xu Min I Hu Xiaobo I Liu Zhenyu
Experimental investigation on the impact force of the dry granular flow against a flexible barrier
Abstract To reveal the composition and distribution of the impact force of the dry granular flow against a flexible barrier, five groups of physical experiments in different slope angles have been carried out. The flow velocities, flow heights and tensile forces of the cables were measured using the high camera and the load cells. Then we developed a model to calculate the total impact force of the dry granular flow against the barrier based on the tensile force of each cable. The results show that the main components the distribution of the maximum impact force vary with the pileup characteristics of the dead zone. The distributions of the maximum impact force change from linearity to nonlinear with the increase in the proportion of the impact force of flowing layer in the maximum impact force. The hydro-static model, the hydrodynamic model and the limit equilibrium method were using for the estimation of the maximum impact force, respectively. Compared with the estimated results, the hydro-static model is more suitable for estimating the maximum impact force of the dry granular flow when the pileup height is five times greater than the flow height. The empirical static coefficients have close relationship with the ratio of the pileup length to the pileup height. Keywords Dry granular flow . Impact force . Flexible barrier . Pileup heightXiao Siyou and Su Lijun contributed equally to this work. Introduction Flexible barriers have been widely used for the mitigation of mountain hazards such as rockfall (Gottardi and Govoni 2010; Kwan et al. 2014), debris flow (Wendeler and Volkwein 2015; Kwan et al. 2019) and snow avalanche (Margreth and Roth 2008) because of their efficient protection capability and installation. However, many flexible barriers failed because of the impact of debris flows. To reveal the reasons of the failure of these barriers, the structure of the flexible debris flow barrier should be clarified firstly. Figure 1 shows that a flexible barrier failed under the impact of a debris flow with the volume of 30 m3. This flexible barrier was installed in a gully located in the Zhangjiakou, Hebei, China. The vertical joints and cracks of the mountain body in this gully are very abundant. Many loose materials are accumulated. The gradation of the loose materials is distributed within the range from 5 to 50 cm. The width of the gully is about 9 m. The slope angle of this gully is about 40° and its outlet is near by the railway tunnel entrance. The impact force of the debris flow results in the upper cable being greatly deformed, as shown in Fig. 2. Then, the steel post was titled and the brake device was failure substantially, as shown in Fig. 3. The structure of this barrier is the same as a flexible rockfall barrier. However, unlike the flexible rockfall barrier, the dissipation of the kinetic energy of the debris flow by the f
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