[M-IS16] Geophysical particulate gravity current

[MIS16-05] Comparison of numerical simulation results for landslide-triggered debris flows considering the liquefaction state of fine sediment

*Norifumi Hotta¹, Junichiro Tobe¹, Yuichi Sakai², Yuki Nishiguchi³, Taro Uchida⁴ (1.Graduate School of Agricultural and Life Sciences, the University of Tokyo, 2.Faculty of Agriculture, Utsunomiya University, 3.CTI Engineering Co., Ltd, 4.Faculty of Life and Environmental Sciences, University of Tsukuba)

Keywords:debris flow, numerical simulation, fine sediment

Evaluation of finer sediment behavior within debris flows leads to a higher reproducibility in the numerical simulations of debris flow propagation (Nishiguchi et al. 2011). We carried out numerical simulations for six landslide-triggered debris flows considering the liquefaction state of finer sediment and compared the results with the in-situ debris flows. The numerical simulations were performed based on shallow water equations with the leap-flog scheme introducing the constitutive equations for a debris flow (Miyamoto and Itoh, 2002), and two entrainment rate equations (Takahashi and Kuang, 1986; Egashira et al, 1988) were tested. The liquefaction state was evaluated using the model proposed by Sakai et al. (2019). First, the final results of one-dimensional calculation were compared with detailed records such as deposition depth and bed width obtained immediately after the debris flow occurrences. Then, the inundation area was compared after two-dimensional calculations for four cases terrain model was available before the debris-flow event. The results showed better reproducibility when considering the liquefaction state in all the tested cases. The best performances were classified into two types: obtained with the fixed parameter for the liquefaction state or the variable parameter reflecting the kinematic condition of debris flow. The results of the two-dimensional calculation were consistent with the one-dimensional calculation. The two settings of liquefaction for optimization infer that landslide-triggered debris flows can descend as a debris flow with well-mixed materials with the characteristics affected by kinematic conditions or as a mass movement closing to landslide in which the excess pore pressure is maintained.