唐家山堰塞体渗流稳定及溃决模式分析

SEEPAGE STABILITY ANALYSIS AND DAM-BREAKING MODE OF TANGJIASHAN BARRIER DAM

在准确获取唐家山堰塞体地质结构(从上到下依次为①层碎石土、②层块碎石和③层似层状碎裂岩3层结构)及相关渗透参数基础上,采用Visual Modflow可视化三维软件,模拟4种堰塞湖水位(710,720,730和740m)条件下不同土层的渗流速度和渗透坡降,表明由于②,③两层颗粒粗大、渗透性好,总体表现出稳定流的渗水特点,整体坡降变化稳定,中间不会出现如低渗透黏性土的紊流状态、渗透坡降出现拐点以及管涌渗透特点。而下游侧①层碎石土由于沿第③层形成的贯通性渗流在下游侧穿越该层渗出形成的最大坡降会大于允许坡降,将导致堰塞体下游发生零散或局部渗流破坏,且临界堰塞湖水位为726m。随堰塞湖水位抬升,整个堰塞坝体出现的溃决模式为:下游侧表层碎石土层因渗透破坏和溯源侵蚀,同时因进口段地表水流漫顶淘刷,最终导致上部第①层碎石土被侵蚀、淘刷带走。随着第①层被淘刷、水流速度加大又进而会带动第②层块碎石被逐渐冲刷下切,但不会发生整体溃决,而第③层似层状碎裂岩将保持稳定,侵蚀和淘刷的下限深度就是第③层似层状碎裂岩顶部。

Based on accurately obtained data of Tangjiashan barrier dam on geological structure（three-layer structures from top to bottom：gravel soil,blocks and gravels,stratoid cataclastic rocks） and the relevant parameters,using the Visual Modflow,which is a three-dimensional visualization software,seepage field of the dam under four conditions of water levels（710,720,730 and 740 m） of the dammed lake are simulated.According to the results of simulated calculation,each soil layer′s seepage velocity and seepage gradient are calculated,and the analytical results show that the first and the second layers have the characteristics of coarse particles and high permeability,so the overall performance is of a stable flow,with the characteristics of seepage and stable change of overall gradient,and it will not have turbulent conditions of low-permeability clay,inflexion of seepage gradient and the characteristics of piping.The maximum seepage gradient in gravel soil of the first layer is more than allowed gradient in the transition between the first layer and the third layer,so it will cause sporadic or partial seepage destruction on downstream of barrier dam.And simulated results show that gravel soil of the first layer will experience seepage failure when the water level of dammed lake is more than 726 m.With the uplift of water level,the dam-breaking mode of overall barrier dam is that gravel soil of the first layer will be eroded and washed away by the seepage failure and head erosion,also by the down-cutting caused by overflow.The blocks and gravels of the second layer are gradually washed away and down-cut because the first layer is washed and water velocity increased,but it will not happen overall breaking.The stratoid cataclastic rocks of the third layer will remain stable,and the depth of erosion and down-cutting is the top of the third layer.