Study Of Some Key Problems Of Civil Engineering In Tianjin NO.1 Subway

Tianjin Subway No.1 Line is the most important line in the plan of Tianjin express rail transit system, the construction of which will not only perfect the municipal infrastructure of Tianjin, but also play an important role both economically and politically in promotion of reasonable urban layout, improvement of communications structure and maintaining sound biological environment. This dissertation covers analysis and research on several key technical problems involved in the civil engineering of Tianjin Subway No.1 Line, including influences of shield tunneling on ground surface upheaval and subsidence, applications of SMW construction method in construction of foundation pits, earthquake resistance and mutual influences of double-deck subway station crossed underground tunnels, etc. The analysis results are verified by measured data and several valuable conclusions have been obtained, allowing an accumulation of experience for design and construction of Tianjin Subway No.1 Line, and at the same time, a reference available for other subway projects. The dissertation mainly focuses on the following aspects:(1) Based on the on-site measurements on the shield tunneling section from Xiaobailou to Xiawafang, ground surface and stratum upheaval and subsidence curves, lateral displacement curves of stratums at different depth are presented; deformation rules of surrounding soils during shield tunneling with pressure on soils are analyzed and summarized; this dissertation also includes 3D finite element modeling established by finite element software to make dynamic simulation of shielding tunneling. Comparisons with data from on-site measurements and analysis show that results from finite element calculations are in good agreement with data from the actual measurement, and it shows that the modeling can fairly reflect practices in construction, which provides a theoretical basis for future subway construction in Tianjin.(2) Several problems in the special geological conditions in Tianjin are studied based on various tests in construction of foundation pit supports at No. 3 gateway of the Honghuli station. Such problems studied include ratio between water and cement in the SMW construction method that uses secondhand steel rails to replace large specification H profiles, roles of steel rails in cement-soil retaining walls, influences of foundation pit excavation on horizontal displacement of the steel rail-cement soil combination walls and ground surface subsidence and recovery of steel rails; and the tests made in the construction include construction of rail-cement soil combination walls, bending-resistance of the combination walls, horizontal displacement of the combination walls, ground surface subsidence and steel rail pull-out, etc. All the tests and studies have provided references to the future engineering designs and constructions. The dissertation also includes finite element simulation of the foundation pit supports, and it is compared with the test data. The comparison and analysis prove correctness of the calculation program and parameters selected.(3) As underground structure earthquake-resistant analysis is much less mature than that of the ground structures, it is absolutely necessary to make earthquake-resistant analysis for the subway structure, especially crossings of subway tunnels. In this dissertation finite element method is used in analysis on seismic reactions of crossed subway tunnels in the Tianjin geological conditions, in studies on changing rules of displacement, inter-layer displacement and inter-layer stresses of the upper and lower deck of subway stations under earthquakes. Besides, this dissertation also includes earthquake-resistant analysis on subways under stratified geological conditions at different depth underground and different weak stratums, which reveals seismic response rules of crossed subway tunnels in different geological conditions, providing instructive opinions for designers of subway stations.