Research On Groundwater Control In Complex Excavation Depth Foundation Pit

In recent years,the majority of the foundation pits are excavated for building group and complex depth.They have the characteristics of deep excavation,complex plane shape and different excavation depth.When there are different excavation depth in the same foundation pit,dewatering has different effects on the foundation pit,and we need to take different measures.According to the different methods of deep confined water truncation,water-proof curtain can be classified into cutting off all the confined water,only cutting off the deep pit's confined water,cutting off part of foundation pit's confined water and without water-proof curtain of deep confined water.In the design of foundation pit engineering,according to the foundation pits' different excavation depths and areas,how to select and setup the dewatering measure and water-proof curtain,and analysis the effect of confined watet's drawdown on the foundation pit and the surrounding environment is a problem needed to be solved urgently at present.Based on pumping test of the Tianjin metro line 6 hotel west-road station project,using the analytical method and numerical simulation analysis,determine hydrogeological parametes with pumping test data to provide the basis for optimization of curtain setting.Through the comparison and analysis of the dewatering effct with the four kinds of water-proof curtain,find that the water-proof curtain cutting off the confined water together or only cutting off the deep pit's confined water can effectually control peripheral water's drawdown and ground surface settlement;when the water-proof curtain cut off part of foundation pit's confined water or don't cut off confined water,the settlement is far greater than the former two.Compared with no cutting off the confined water,the water-proof curtain cut off part of foundation pit's confined water can reduce the settlement greatly.The shorter the time is,the closer the distance is and the longer the water-proof curtain to cut off part of foundation pit's confined water is,the greater the decreasing degree is.But the dewatering will result in larger settlement in both ends of the deepened curtain.When change the depth D-value between the deep and shallow pit,the settlement with curtain cutting off all the confined water has little change,and the settlement with curtain cutting off the deep pit's confined water don't change approximately.When the deep pit excavation depth is small,the drawdown and ground settlement with curtain cutting off part of foundation pit's confined water or without water-proof curtain of deep confined water are small,but with the increase of the deep pit excavation depth,the drawdown and ground settlement increase significantly.When the curtain cut off all the confined water,because the drawdowns of he deep and shallow pits' water is same,if change the area of deep pit,he design of the foundation pit drainage project can be unchanged,so the surrounding ground settlements are the same.When the area of deep pit is small,the settlements with curtain cutting off all the confined water or only cutting off the deep pit's confined water are similar;But when the area is large,the difference values increased.When the curtain cut off part of foundation pit's confined water or don't cut off the deep confined,if the area of deep pit is small,the dewatering area is small,and the settlement is also small,but it significantly increases with the area increasing.