Study On The Cover Excavation Half-reverse Method And Water Intake Program Of The Commercial Underground Space Construction For Urban Air Defense

With the development of urbanization,some inevitable problems arise,such as insufficient urban land,traffic congestion,environmental pollution,earthquake disaster,and space saturation are getting worse and worse.Therefore,the development and utilization of underground space have become more important.Now,open cut method is usually to excavat commercial underground space construction for urban air defense.However,if the construction site is located in the main road of urban central area,the excavation makes a great impact on the surroundings and seriously interfere with the traffic.Meanwhile,the emergency water intake of the commercial underground space construction for urban air defense relies more on external water sources.Water demand can't be satisfied during the wartime.Therefore,it is of great practical significance and practical value to study the cover excavation half-reverse method and emergency water intake program of the commercial underground space construction for urban air defense.Based on a commercial underground space construction site for urban air defense project in Zhenjiang City,Jiangsu Province,three different construction methods are compared,and the cover excavation half-reverse method is determined as the optimal construction method.The construction process of the cover excavation half-reverse method is further summarized.The surrounding environmental effects caused by the excavation of the foundation pit are studied.The variation regularity of the surrounding buildings vertical displacement caused by the excavation process is revealed.A wartime emergency water intake program suitable for the commercial underground space construction for urban air defense is proposed.The main research contents and results as followed:(1)Based on the analysis of the hydrology geology condition of the construction site of the commercial underground space construction for urban air defense in Zhenjiang,three excavation construction methods of commercial underground space construction for urban air defense are proposed,i.e.cover excavation half-reverse method,pipe jacking method as well as cover excavation reverse method.The excavation conditions of the three methods are compared by numerical simulation method.The deformation behaviour of foundation soil under different working conditions is calculated.According to the influence of excavation on the surrounding environment and traffic,Three excavation construction methods' deformation law is determined.Then,through the combination of AHP and value engineering theory,six factors including construction complexity,construction safety,construction cost,construction progress,impact on traffic and impact on the surrounding environment are considered.The function coefficients,cost coefficients and the ratio value coefficients of the three methods are calculated.Finally,it is stated that the cover excavation half-reverse method is the most suitable choice for this project.(2)According to the analysis of factors,such as geological conditions,the hydrogeological conditions,the surrounding structures,the excavation depth of the foundation pit and the coordination of construction organization of the construction site,the foundation pit is divided into 12 sections for design.Based on the design and calculation of the foundation supporting structure,the supporting structure combining the bored pile,the three-axis mixing pile,the steel sheet pile,the H-beam,the roof and the pipe pile is summarized.In order to minimize the impact of construction on traffic,the construction process of the foundation excavation is divided into two parts including north and south sides.The analysis shows that the cover excavation half-reverse method is applicable to the commercial underground space construction for urban air defense,which is the excavation is done first and then the reverse is used to cover.Using the three-dimensional finite element analysis method,the dynamic simulation of the foundation excavation construction is carried out.The results demonstrate that the maximum overall displacement of the foundation soil(127mm)is distributed at the bottom of the foundation pit.The maximum vertical displacement of the surface soil on the north side of the road is 9.28 mm,and the maximum horizontal displacement is 15.39 mm.The maximum deformation of the supporting structure is 15.4mm.The maximum vertical displacement of building foundation on the north side is 8.977 mm,and the maximum vertical displacement building foundation on the south side is 8.242 mm.Overall,the effect of excavation on the surrounding environment is small therefore the design requirements can be met.(3)According to the underground water conditions,the emergency water intake program of commercial underground space construction for urban air defense is proposed,which is using tube well to intake deep underground water.The program can both meet the feasibility and cost control.Using the three-dimensional finite element analysis method to predict the environmental effects of emergency water intake during wartime.The results show that the impact of short-term emergency water intake on the surroundings during wartime is within control.