Deep Level Soil And Water Hammer Wall Construction Method And Engineering Practice In Deep Foundation Pit

The Foundation Pit project is a very strong comprehensive system engineering which mainly includes the design,the construction,the dewatering,the monitoring and the earthwork excavation.The earth pressure that the support system bears has space-time effect.At present,the most commonly used types of foundation pit support system are row piles,diaphragm walls,gravity-type cement wall,soil nailing wall,inverted arch wall and so on.For the deep Foundation pit,it generally takes the traditional pile + support + water-stop curtain support system.The main content of this paper is based on the practice of the Foundation Pit Engineering in Changzhou Wujin Xintiandi,and discusses and summarizes the application of the construction method of multistage dewatering soil nailing in deep foundation pit under the geologic conditions of confined water area and cohesive soil layer as the pressurized water roof and floor slab.The application of this support method breaks through the rules of the Technical specification of building Foundation pit support,which limits the application scope of the soil nailing wall to the digging depth within 12 meters.It also breaks through the traditional underground water treatment mode of the deep foundation pit and adopts the open precipitation model boldly.This project is the first time to use piles and steel pipe casting to solve the problem of supporting the important high-rise structure in the middle of deep foundation pit.This research is expected to provide reference for similar foundation pit engineering design and construction in the future.The main research contents of this paper are as follows:1.This study expounds the source of this method: it is applicable to the confined water area,with cohesive soil as the top and bottom roofs of pressurized water,and more than 12 m deep foundation pit.This soil nailing wall construction method with multistage dewatering in deep Foundation pit is a open deep multistage precipitation and soil nailing wall supporting system,the former is to achieve the purpose of "stop water" through the open precipitation through forming dynamic stop water curtain,the latter is to support the structure.2.Three similar engineering practices can be visually demonstrated deep open precipitation in different support forms of the application in the pressurized water with hard plastic-plastic clay,commonly known as "crust layer",as roof.Through the analysis of the final monitoring data,the deep open multistage precipitation can be popularized in the future.3.The engineering application of deep multistage precipitation is expounded through the foundation pit support project in Changzhou Wujin Xintiandi,and the analysis of the general idea of the design process concretely elaborates the design idea and the step of the work method.The construction project is the first time to use piles and steel pipe support form to support deep foundation pit with a high-rise structure,228 meters high height TV tower,in the middle of the foundation pit.It is necessary and difficulty to pay attention to the protection of the TV tower during the construction process,its overall stability and deformation control is very important.After the foundation pit excavation,only 1/3 of the tower foundation pile is located below the excavation surface of the pit bottom,and the concrete construction procedure and control methods are analyzed and summarized in the paper.4.This paper uses the finite element analysis to compare the tower base deformation data and the actual monitoring data,and the result shows that the actual settlement data is about 1.3 times of the calculation data of finite element analysis,but the overall settlement is uniform which satisfies the normal use of the TV tower.The finite element analysis result is a good reflection of the influence of the excavation on the TV tower.It provides a favorable reference for the related design,and further verifies the rationality of the design scheme of the foundation pit support.During the earthwork excavation,the tower subsidence value is large,but the uneven value is very small,all can satisfy its normal use request.Anyway,finite element analysis is to simulate the perfect construction condition by controlling its inclination rate to ensure the uniform settlement of the TV tower,it is suggested that the tower should be the center of the Earth excavation and the erection should be symmetrical construction.