Assessment Of Construction Methods The Top-Down And Excavation Under Cover Board Used In Harbin Subway HLJ Univ. Station

There are many kinds of underground projects and they have engineering varied characteristics, so the corresponding excavation technology are different. Take cities'subway as an example, the subway stations'construction can choose open method, mining method , top-down construction method, cover and cut method according to different geological conditions, the working environment, time limit for project and safety factors.The type of some sections of Harbin subway Line 1 is loess areas, the groundwater level of these areas is very low, so they have little impact on the No. 1 line subway construction; character of soil is good and excavation is convenient. For this section of loess area without groundwater and good soil character, either top-down construction method or cover and cut method for digging can be chosen to construct underground railway building. In this paper, the subway station of Hei longjiang university of Harbin No. 1 subway line will be taken as an example. Through comparing every aspect of the reverse method and covered method and optimum compared analysis, this paper not only provides a basis for the design and construction but also gives theories of methods of evaluation for subway construction.This paper compares the force and deformation of structure which constructed with top-down construction method and cover and cut method. Of course, economic, social and environmental benefits, the prevention and application efficiency and so on are evaluated and analyzed also.The construction process of the two methods are divided into several working conditions when compared the force and displacement, and they are also simulated by Large-scale and generic finite element software—Ansys. The process of top-down construction method is divided several working conditions according to excavation of soil and order of components'casting on the ground of Discrete Principle. Force and mechanics characters of structure of different working condition are exhibited by analyze each working condition's inner force and displacement of structure.The simulant effect of the construction process is achieved by using alive- dead element of Ansys, so only one finite element mesh partition is adopted when calculated entire excavation process. This simulant analysis reflects the actual construction of the dynamic process;In cover and cut method structure calculation, using ANSYS freedom coupling, freedom of the main structure and retaining piles are coupled so as to retaining piles and same side wall have the same deformation;Using ANSYS simulation, in working stage, the force and displacement of structures that constructed by reverse method and top-law method are nearly the same, in contracture stage, the force and displacement of structure in some working condition are rather Considerable, especially using top-down construction method , so temporary braces are needed.During evaluation analysis of the two methods'economic, social and environmental benefits, effectiveness of prevention and application, Fuzzy comprehensive evaluation method is used to make optimization analysis. In many conditions of the Hei longjiang university's subway station of Harbin No. 1 subway line, top-down construction method is the Optimal Methods.