The Study Of Transfer Subway Key Construction Technology And Semi-inversed Cover Excavation Method In Confined Water Layer

The Hongqi Road Station of Tianjin Metro Line6is a T-shape transferring station with three levels of underground structures. The technical difficulties during the construction include:(1) the control of disturbance due to pit excavation to the operational station of Metro Line3and shield section.(2) The water leakage of retaining structure, dewatering, excavation and building protection during the construction of super deep pit by using the semi-inversed cover excavation method under high groundwater level and complex hydraulic geology. The groundwater level is-2.58m and the depth of the pit at shield well is24.5m. There are residential buildings with6levels built in1980s only11m far away from the north end well of the pit. The unclear aquifer layering resulted in difficulties of dewatering and water bursts. Therefore, the construction of the station is very difficult technically. Based on the study, such difficulties were overcome. The major research work and achievements obtained from the study are as follows.(1) A set of technology detecting leakage of underground continuous wall of deep pits. By using an integrated method of analyzing the construction of underground continuous walls, injecting paint to the joint of enclosure structure plus water pumping in the pit, dynamic monitoring of water leakage and pumping tests, the water leakage location of the pit enclosure structure was estimated, which provided a basis to the leakage treatment of the enclosure structure.(2) An integrated technology of leakage treatment of underground continuous walls was established. By using twin high pressure jet grouting piles, injecting double grout to the joints of underground continuous walls, and sealing the steel plate of the inner joints, the leakage risk of underground continuous walls was reduced.(3) Through dewatering calculation and construction verification, an integrated dewatering technology for deep pits with a water pressure layer was proposed. By setting dry well, depression well and water collection pit to pump water, the water level was lowered beneath the pit and a safe bottom sealing was achieved.(4) A key construction technology including excavation using semi-inversed cover excavation method, medium plate, separating underground continuous walls at transfer joints, grouting side walls was established. Adopting detecting before excavation, excavating50cm deep at corresponding side location when constructing medium plates, the water proof plate and vertical reinforcement of upper side walls was inserted into lower excavation part and filling medium coarse sand was back filled to the bottom. Oblique grouting was applied to the transfer joints before the demolishing of the underground continuous walls to seal the pressured water. The grouting holes at side walls were preserved in the construction of medium plate construction in order to ensure the safety of excavation, save reinforcement joints and ensure side wall construction quality.(5) The protection technology and deformation patterns of shield segments at transfer stations was summarized. By rigidly jointing shield segments at transfer stations, sleeve-valve-pipe grouting to the ground, and strengthening monitoring using static leveling, the differential settlement of the structure was controlled.