蓄水期库岸古滑坡的水动力学响应监测——以三峡库区泄滩滑坡为例

水库岸坡失稳是伴随水电工程建设而产生的一种地质灾害，一般认为主要是由于水库蓄水或运营导致岸坡水动力条件的不利演化造成的。国内外水库岸坡失稳的实例很多，但是岸坡的水动力条件演化过程主要以渗流计算所获得的渗流场作为依据，缺乏系统完整的现场监测资料。以三峡水库蓄水为契机，在湖北秭归县泄滩古滑坡体上建立了一套自动水文监测系统，监测内容包括水库水位、滑坡体水位、渗压与降雨量等。从监测成果来看，岸坡的水位(或渗压)上升速度明显滞后于库水位上升速度，滞后时间与岸坡的渗透性有关，滑带、滑坡影响带和基岩的渗透性相对较弱，滞后时间较长，但是滑坡体的渗透性良好，滞后时间较短；水位观测井的观测成果存在误导，需要结合观测井结构进行分析，建议尽可能使用标准管结构；降雨引起的滑坡体水位上升量和滞后时间与降雨强度关系密切，降雨强度越大水位上升量越大，水位开始上涨的时间越短。因此，对降雨的影响分析有必要考虑雨型，确定合适的基准时间单位。就泄滩滑坡而言，以小时为基本时间单位较为合适。

HYDRODYNAMIC MONITORING OF A PREEXISTING LANDSLIDE DURING RESERVOIR FILLING--A CASE HISTORY OF XIETAN LANDSLIDE,THE THREE GORGES RESERVOIR

Reservoir slope instability is a geological hazard induced by construction of hydroelectric project and is generally believed to be caused mainly by the unfavorable change of hydrodynamic condition in the slope due to reservoir filling and/or operation. Many cases of reservoir slope instability can be found both in China and abroad, the evolution of the hydrodynamic conditions,however,is mainly obtained by seepage analysis,while the systematic and complete field instrumentation data can rarely be found. Taking the opportunity of filling the Three Gorges Reservoir,an automatic hydrologic monitoring system is implemented to monitor the hydrodynamic evolution of a preexisting landslide,Xietan landslide in Zigui County,Hubei Province,China. The system includes the monitoring of reservoir water level,water level in boreholes,seepage pressure and precipitation,etc. The comprehensive analysis of the monitored data shows that the rising speed of water level (or seepage pressure) on the reservoir bank lags behind that of the reservoir filling and the lagging time is closely related to the permeability of materials of the bank. The weaker the permeability of the slip band,sliding-disturbed zone and bed rock are,the longer their lagging time is. If the permeability of the main body is quite good,then only a short lagging time can be observed. Water level data from observation wells are misleading and should be analyzed with the well structure,and standpipe should be used whenever possible. Rainfall-induced water level rising in the main body and its lagging time are greatly influenced by rainfall intensity. Heavy rainfall takes less time to infiltrate into the slope and induces higher water level rising. Therefore,for the analysis of rainfall influence,a basic time unit should be determined according to the rain type. Basic time unit of hour is feasible for Xietan landslide.