基底侵蚀对高速流动性滑坡运动性影响的模拟分析

NUMERICAL INVESTIGATION ON IMPACT OF BED ENTRAINMENT TO THE MOBILITY OF RAPID FLOW-LIKE LANDSLIDES

高速流动性滑坡运动距离远,破坏性强。这类滑坡在运动过程中常裹挟大量的松散物质,导致滑坡的体积和致灾范围增大,该现象被称为基底侵蚀效应。以往的研究指出基底侵蚀效应对这类滑坡的运动性有显著的影响,但却很少有研究考虑其对滑体性质的影响,以及如何对其进行量化。因此,本文基于动量守恒原理建立了考虑基底侵蚀效应的滑坡运动模型,利用有限差分法求解,并依据滑坡的侵蚀深度来计算侵蚀导致的滑坡性质变化。利用改进的模型对陕西泾河南岸的西庙店滑坡进行模拟分析。结果表明,滑坡运动可分为启动加速阶段(0~5 s)和运动减速阶段(5~14 s)。在启动加速阶段,基底侵蚀程度低,对滑体运动的影响较弱。而在运动减速阶段,基底侵蚀效应降低了滑带土强度,对该滑坡的运动产生了明显的促进作用,致使其发生远程运动。此外,对比考虑和不考虑基底侵蚀两种工况的模拟结果还发现,考虑这种影响时,模拟所得的运动范围及地形与实测吻合良好,而未考虑时模拟所得运动范围明显偏小。因此,本文的模型可对这类滑坡的运动过程进行更为有效的模拟。

Rapid flow-like landslides are characterized by their high mobility and catastrophic consequences. These landslides tend to entrain a great amount of loose materials along their travelling paths,resulting in the enlargement of landslide volume and covering area. This phenomenon is called bed entrainment/scouring in literatures. Although previous studies showed that bed entrainment was a significant factor influencing the mobility of rapid flow-like landslides,few of them considered its impact on the rheology of the sliding mass,and needless to say quantifying this impact in numerical modeling. Therefore,this paper proposes an improved finite difference model based on momentum conservations of both the landslide and erodible mass. In this model,the influence of bed entrainment on the rheology of a landslide is quantified by modifying the rheological parameters of the landslide according to the calculated entrainment depth. Then the Ximiaodian landslide,a typical rapid flow-like landslide located at the south bank of the Jinghe River in Shaanxi Province,is simulated by the new model. It shows that the run-out process of this landslide can be divided into the rapid acceleration stage(0 ~ 5 s) and the slow deceleration stage(5 ~ 14 s).During the acceleration stage,the extent of entrainment is small,so its impact on the motion of this landslide is slight. However,the entrainment obviously promotes the mobility of this landslide at the deceleration stage by reducing the basal resistance. In addition,the modeling results of considering and not considering bed entrainment show totally different patterns. The simulated covering area and final deposit agree well with the measured data when adopting the improved model,while those neglecting the impact of bed entrainment-induced rheology change are obviously smaller than that of the fact. It turns out that the new model proposed here is more suitable for simulating those rapid flow-like landslides with similar bed entrainment phenomenon.