Research Of The Construction Mechanics Effect During Large Excavation To The Subway Station Built By Pipe-Roof Pre-Construction Method

Pipe-roof Pre-construction Method (PPM) is a new type excavation technology of constructing underground space in domestic use for the first time. With the support of large diameter steel tube, which is relative big stiffness, in the early days, one tube goes through another to form tube gallery space. The permanent structure of underground is pre-built in it, and then the big span underground space was excavated by the support of permanent structure. PPM has the characteristics of safety construction, no need down groundwater, small surface subsidence, short construction period, available large space, less effect to the ground transportation, surrounding commerce and the residential life etc., which has good social and environmental benefit. PPM are suitable to the projects of soil or soft and no cemented pebble and sand of the Pleistocene strata, which are not suitable for open excavation underground construction, and the dense ground building, the busy transportation, densely covered underground pipeline and the strict request for the surface subsidence of the city, especially to the urban underground hub project and the underground project construction under the traffic artery.PPM is a new type excavation technology of constructing underground project worthy of study and summary. The study of it can provide guidance for the first application in China and improve the design theory and construction techniques, which can form the underground project constructive and normative technical documents fit for our stratum condition and national condition, and it has the vital significance to promote the development and innovation in our country’s underground engineering construction. By collecting the previous material, theoretical analysis, numerical simulation technology and field tests, some innovative research conclusions are as follows.(1) It is the first time to carry on the system research of PPM, especially for an important process-the large excavation inside the underground structure by PPM. And it is also combined with the engineering practice to analyze and summarize which provide a scientific guidance for the engineering practice and provide the theory basis for PPM to design, construction, monitor, and provide reference and guidance to form the underground project constructive and normative technical documents.(2) By the study of PPM including the supporting theory, method of building construction technology, the simulation test and engineering practice, the interaction law of the lining structure and surrounding rock has been obtained. The computation model of PPM and calculation method of the load on the wall lining structure has been set up, and the optimization design method of the pipe lining structure built has been discussed, which have been provided guidance for PPM to improve the building technology of underground space.(3) Through the study of the stratum deformation characteristics, stratum loss and the law of surface subsidence caused by PPM and the analysis on the engineering practice, the deformation law of PPM to the ground settlement and the lining structure had been got. Besides, the calculation model and the control measures of the ground settlement of PPM have been put forward.(4) The numerical model of large excavation of PPM in underground has been built first by Fast Lagrange Analysis of Continue (FLAC), and the stress and the strain characteristics and the variation of the underground structure and the formation has been got, which have been provided reliable guarantee for the completion.(5) The field test of the large excavation construction stage of PPM has been done on the Xinle Subway Station of the metro line2in Shenyang, and the informatization construction of building underground space by PPM has been realized. In addition, the surface subsidence and mechanical response parameters of the lining structure has been gained by PPM, and the field construction test data has been accumulated which verified the theoretical analysis and numerical simulation results and ensured the first successful application of PPM in China.