| Based on the present situation of top down construction for underground engineerings, the author illustrated the advantages, disadvantages and technology of top down construction and analyzed some key problems for top down construction.The diaphragm wall of top down construction not only supports the horizontal loads at stage of the temporary construction, but also bears vertical loads, as a part of the main structure, the outer wail of the basement. The author gave a detailed study on means to caculating method of loads, internal stress, and sedimentation with the main structure. Appropriate measures had been taken to deal with the joints of construction and structure.The center brace, also named guide pillar, serves a dual purpose, not only surpporting all the loads at stage of construction, but also transmitting upper loads down to the foundation, as a part of the column after the top down construction, Its designing and construction are more strict. The author analysed the methods of designing and construction for center brace, and proposed several key techniques that can improve the quality of the center brace.Bing top down construction is carried out, the underground structure construction, including soil engineering, concrete casting and formwork, becomes more complicated and more strict. The paper gives a detailed research on the problems, and brings forward corresponding solutions.The monitor of the deep pit is also the important problem to the top down construction. The paper also analyzes the monitor method for top down construction.At last, according to the practice projects, the thesis gives a particular introduction for the application of construction process and the application effect of the top down construction. And the author also put forward several proposals about top down construction in the paper, as well as summarized and advanced the developing trend of top down construction and the problems which should be made gret efflorts to solve.
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