Study On The Dynamic State Of Groundwater In Jinlong Mount Under The Effect Of Rainfall And Reservior Impounding At Ertan Hydropower Plant

The stability of the bank slope is closely related to the safe operation of the hydropower station,while the groundwater dynamics in the slope is an important factor affecting the stability of the slope.Reservoirs,especially the periodic fluctuation of reservoir water and will greatly change the physical and mechanical properties of rock and soil mass in its dynamic change in the saturated-unsaturated state for a long time,adverse to the long-term stability of the slope.In order to find out how large the influence is and whether it will exert a fundamental influence on the slope stability,it is necessary to master the distribution characteristics of the groundwater seepage field under the condition of reservoir water level fluctuation and rainfall.In this paper,the creep characteristics of the II reservoir slope at the first gorge of the two Longtan Hydropower Station are studied,and the groundwater dynamics of the reservoir side slope under the action of rainfall and reservoir water level are studied.Based on the analysis of the engineering geological environment conditions in the study area,and according to the monitoring data,the variation law of the seepage field of the creep groundwater in the II area of the Longshan gorge slope is analyzed and summarized under the condition of the fluctuation of the rainfall and the reservoir water level.Accordingly,modification and generalization of valley slope creep area II geological model,a two-dimensional Visual-Modflow model to study the reservoir before and after impoundment under different conditions of seepage field characteristics,can well reproduce the variation of seepage monitoring of slope,slope stability prediction is provided according to the theories and methods of analysis and the deformation process.Through the analysis and research,the paper mainly draws the following conclusions and results:(1)The monitoring data such as rainfall,reservoir water level,infiltration water level and corresponding groundwater flow and deep deformation of landslide are obtained before and after the storage of Ertan Reservoir,and the example is provided to study the seepage field of bank slope.(2)Before the reservoir impoundment,the rainfall infiltration is the direct factor to change the groundwater level in the landslide,the greater the rainfall,the more the groundwater level rises,but the delayed rainfall is about 1 months.The lifting effect of underground water level slope is mainly affected by the Yalong River water level,although they are affected by rainfall,but the effect is small.When in the flood season river rises fast,osmotic pressure water level rise time lag slightly.Three point method is used to determine the Jinlongshan valley slope water flow direction,before the storage of reservoir the rainy season groundwater flow direction is S22 ° W,dry season is S7 ° W.(3)The early storage period,each measuring hole seepage pressure level and water level changes are basically the same,the underground water level with the rapid fluctuation of reservoir water level synchronous lifting,lifting rate and water level of groundwater in the slope are almost the same,both of them maintain good correlation.In the initial stage of rapid reservoir water storage,the increase of water level in the measured pore water pressure slightly lags behind the increase of reservoir water level,but the lag time is short,which reflects the relatively good permeability of the slope.(4)During normal operation,the groundwater level in the slope rises and falls with the fluctuation of the reservoir water level,and there is almost no lag time.When the reservoir water level rises or falls,the rate of groundwater lift is almost the same as that of reservoir water,and the two maintain good correlation.Due to the prolongation of the infiltration path,the groundwater level and the reservoir water level in the normal operation period reach the new dynamic balance of the groundwater level.In the case of the reservoir water level,the groundwater level is about 1m lower than that of the test run slope.(5)On-site monitoring shows that the osmotic pressure is too small due to the large hydrodynamic pressure in the direction of the osmometer.The numerical simulation results show that the simulated groundwater level is larger than the infiltration water level,which is closer to the actual groundwater level,and the trend of simulated water level is consistent with the actual monitoring of the change of the water pressure level.The simulated water level can be used to calibrate the monitoring data,reflects the actual groundwater level changes better,the accuracy of the model is more accurate.