Design And Application On Cofferdam Anti-seepage System For Tongzilin Hydropower Station

Foundation treatment plays an important role in water conservancy and hydropower projects.Its main purpose is to take appropriate measures to improve the foundation conditions,improve the physical and mechanical properties of the building base,enhance the integrity,improve the shear characteristics,reduce the settlement of the foundation,and improve the anti-seepage capacity,so as to meet the needs of the project and ensure the safe operation of the building.The dam site of Tongzilin project is located in a region with steep bank slope and poor geological conditions,especially the overburden of the left abutment of the upstream cofferdam,which is a soft foundation with a thickness of 90 m.It is difficult to prevent seepage and the construction period is short(the construction period is 4 months).It is difficult to form a complete anti-seepage system and achieve good results.Based on this,according to the specific characteristics of Tongzilin hydropower station,this paper studies the cofferdam seepage control mode of Tongzilin hydropower station.The main achievements are as follows:(1)According to the geological and water flow conditions at the dam site of Tongzilin hydropower station,this paper studies the anti-seepage axis of the cofferdam and puts forward the comparison and selection scheme,and selects the economical and reasonable anti-seepage axis,that is,starting from the left guide wall along the direction of the right bank,turning to the S214 highway culvert at the river center,turning from the S214 line reconstruction road culvert,and extending vertically to the mountain along the railway culvert,Form an anti-seepage axis.(2)Combined with the geological conditions of left weir shoulder of Tongzilin hydropower station and the objective requirements,the traditional soft foundation treatment methods are studied,and different schemes are compared,so as to determine that grouting method is a reasonable way to treat the weak foundation of left weir abutment of Tongzilin hydropower station.That is to say,three rows of holes are used for curtain grouting of overburden layer,which are discharged into rock 8.0m in the middle.The distance between curtain grouting holes is 2.0m and the row spacing is 1.0m.The holes are arranged in plum blossom shape.(3)The upstream and downstream Cofferdams of Tongzilin Hydropower Station adopt geomembrane core wall,the deep overburden adopts concrete cutoff wall,the curtain grouting seepage prevention method is adopted under the bedrock,the deep overburden layer of left weir shoulder and the broken rock mass adopt the anti-seepage method of curtain grouting,so as to form a complete closed anti-seepage structure with guide wall and slope.