Research On Several Techniques Of Big & Deep Foundation Pit By Top-down Construction Method

In 1935 Japanp proposed a top-down construction for the first time,by studied and applied through more than 70 years,top-down construction has been applied on many basement of high building and super high building at present. Superiority of propping effect, economic benefits and shorten time limit for a project of top-down construction make it popularize and apply in the whole country. Issue of law of construction technique of top-down construction in Shanghai and Guangzhou city play guidance function to canonical construction, which indicate that development and project going against the craft of way of doing things use and enter a new stage. Thereare still many problems need solving because of difficulty in complexity of construction techniques.This dissertation is carried out research and investigation on base of the largest deep foundation project of shanghai-the foundation pit of Zhongsheng commercial Center, These papers aim at offer supervise function for design and implementation of top-down construction of a certain degree, in order to play a role of casting a brick to attract jadein there, the main contents are as follows:First, starting with the concept of top-down construction,this paper introduce briefly development of top-down construction in home and abroad, technique and procedure of construction,also advantage and limitation of this method.Secondly, The author has done some research on the whole plan of top-down construction method, the layout of the holes of the slabs for excavation and brought out the basic technique requirements which include the security and economics of the project and shortening the total project time.Thirdly,several theories of designing and calculating in top-down construction are discussed. which include the earth stress value model during soil excavation, the designing of the continuum-wall, the load-value choosing and the carrying capacity calculationg of the middle supporting column,the designing of inner supporting beam and differents kinds of nodes in the basement. Fourthly,Using ansys to simulate and analysis several nodes in top-down constration with 3-D nonlinear model.Fifthly,some techniques of top-down construction method are discussed. They are the plumb technology of the column piles ,It is a way of controlling the quality of piles in sites, the structure of joints and quality control were extensively analyzed. also contian the quality control of connect of concrete between new and old.At last, informational method of the top-down construction,which include supervisal of deep foundation, controlling method of differentia settlement and distortion, enhance the incorporate of design and construction in deep foundation pit. and ect.