| With the rapid development of water conservancy construction,the project construction area to the geological conditions more complex areas advance,Especially in the construction of water conservancy projects in the western mountainous areas,often encountered in the karst area reservoir construction,to develop these areas rich in water conservancy and hydropower resources,we must first solve the many problems caused by karst development,such as the reservoir area,dam area karst leakage problem,due to the existence of this poor geological phenomenon of karst,it has a great influence on the success of the main project and the operation period,and even affect the success of the entire project.Therefore,it is important to check the feasibility of decision-making in the construction of water conservancy project to find out the karst development in the project construction area.The Changlangba Reservoir is located in the upper reaches of the Liweidi River in the western mountainous area of Shidian County,which belongs to the tributary of the Shidian River.the right bank of the dam site area is mainly distributed the clastic sandwiched rock in the carbonate rocks of Silurian,developed with dissolved holes,dissolved dissolution and small cave;the left bank of the dam site is mainly distributed in the Upper Carboniferous Woniusi Formation volcanic rock,the contact method of the rock is fault contact,and the fault near the vertical through the dam area.After the reservoir impoundment,the reservoir may leak along the karst channel and the fault in the rock mass,which affects the reservoir efficiencyand even threaten the dam safety.Based on the field geological survey and the preliminary exploration data,From the dam site geological conditions to start,this paper systematically analyzes the karst geologic conditions,karst development characteristics and karst hydrological characteristics of the dam area;Based on the experiment of water pressure,the spatial distribution characteristics of rock mass permeability and the correlation between the karst development characteristics and the permeability of the rock mass are analyzed.This paper describes the possible leakage patterns and leakage channels,and use the hydrogeological method to estimate the leakage amount for the channels that may leak;thenuse Modflow software to simulate the three-dimensional numerical simulation of groundwater seepage field,to obtain the leakage risk and the leakage amount of the possible leakage site,proposed anti-seepage recommendations.The main conclusions are as follows:1)Analysis of hydrogeological conditions of dam area: groundwater type of dam area is divided into phreatic water and confined water,confined water in the study area exists in the right bank of the ridge in the carbonate,phreatic water exists in the whole study area;the dam area of water rock interaction time with the difference of the carbonate rocks mainly calcite saturation the index is less than zero,the groundwater mainly to erosion;showed the calcite saturation index greater than zero in the volcano rock,there is precipitation trend.The analysis of water chemistry in dam site area shows that the main type of water chemistry in dam site area is HCO3-Ca type water.2)The results of geophysical prospecting,borehole data and surface survey results show that: the surface of most carbonate rocks is covered with red clay,and are only concentrated in the ridge of the left bank of the dam site,where the surface dissolved trench,dissolved gaps and dissolved pores are developed,and the joint fissure develops,forming a strong dissolution zone,which becomes the main seepage channel of groundwater.In the vicinity of the dam site is mainly affected by the fault of the river,the fractures and small faults are more developed,and there are dissolved holes,dissolution,small caves and crushing erosive zones,the structure of the cutting combination is easy to form water channel.3)through the analysis of the water pressure experiment data,the permeability of the right bank rock mass is less than 3Lu,the integrity of rock mass is relatively good and the permeability is relatively weak,but the permeability is not obvious in the vertical area,the dam foundation and left bank rock limestone permeability is better,permeability of 4-5Lu;basalt body permeability of 2Lu.4)Through the karst hydrodynamic condition and channel condition analysis,the fissure leakage is the main leakage mode in the reservoir area,and the possibility of porosity leakage and pipeline leakage is small.Dam foundation and the left bank of thin ridge may become the main channel of seepage in the reservoir area downstream and the right bank of the adjacent valley cannot leak.Using the theoretical calculation formula of hydrogeology,the leaking amount of each leaking channel is calculated: When the reservoir water level is 1845 m,the leakage of the dam foundation and the left bank ridge is 1328.52m~3/d.The reservoir leakage is 1037.24m~3/d at 1840 m and the reservoir leakage is 764.87m~3/d at 1835 m,the reservoir leakage is549.23m~3/d at 1830 m.5)Numerical simulation analysis of groundwater seepage field can be seen in the absence of any anti-seepage measures of natural water storage conditions,the water level reached 1845 m,the entire reservoir area leakage of 1406.71m~3/d;themain leakage site to set the corresponding anti-seepage curtain,in the case of seepage curtain leakage of 260.45m~3/d,it is necessary to take the anti-seepage measures to the reservoir,which can effectively reduce the amount of leakage.In the case of full-section seepage control of the reservoir,the lateral movement of the reservoir around the anti-seepage curtain was cut off and the infiltration in the vertical direction was weakened,and the leakage amount was further reduced.Under different water storage levels,the leakage simulation was carried out,the leakage amount is 138.29m~3/d at 1445 m,the leakage amount is 99.83m~3/d at 1840 m,the leakage amount is 36.04m~3/d at 1435 m,the leakage amount is 25.34m~3/d at 1830 m.6)Through the research results in this paper,it can be concluded that the groundwater level in the dam area is higher,the karst of the soluble rock is more developed,and the permeability is larger in the vicinity of the structural belt,and the catchment area and the amount of water in the reservoir area are smaller.It is considered that the reservoir conditions of Changlangba reservoir are poor under natural conditions,and the possibility of reservoir formation is small.After the measures of anti-seepage measures are taken,the water level is 1835 m when the higher reservoir conditions and better economic benefits. |
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