Study On Design Of Beijing Subway Station Deep Excavation Based On Deformation Controlling

ABSTRACT:With the continuous development of China’s economy, Modern city construction, more and more deep foundation pit engineering sprung up, these deep excavations are usually very large scale, super deep excavation, geometric size irregular, site narrow and surrounded by buildings and utilities. The contradiction between deep foundation pit construction scale and technology is becoming increasingly conspicuous. Current strength control design theory has far cannot satisfy the deformation requirements of the surrounding complex sensitive environment. The displacement controlling design is demanded urgently with the development of excavation engineering technology. However, the confusion exists in deep foundation pit design has seriously constrained the scientification, precision and standardization in deep foundation pit construction. Therefore this paper carried out researches on deformation characteristics, mechanism, influences, the influence of deep excavation on environment, control standards, the basic principle and intension of displacement controlling design of Beijing subway station excavation engineering. The main contributions of this thesis are described in the following:(1) Combined with the Beijing city formation and environmental characteristics, Reveals the damage rule of Beijing subway deep foundation pit. In a foundation pit accident, localized shear band was first formed in a certain depth below the surface, then crack development, lead to local ground instability, eventually led to the accident. Groundwater is one of the main reasons that induced pit accident. Use indoor model test get the damage mechanisem and progressive failure characteristics of unsupported excavation, and validation the critical stable depth.(2) A database of67case histories of deep excavations in Beijing is presented. Reveals the deformation characteristics of Beijing subway station deep foundation pit. The general profiles of lateral deformation of bored pile wall are " convex shape". The maximum lateral deformations of all excavations, which range from0.04%H to0.218%H, with a mean value of about0.103%H. The final pattern of ground surface deformation is "groove shape", The maximum values of settlement, which range from0.034%H to0.442%H with a mean value of about0.1%H.(3) According to the time and space law in Beijing subway station, an empirical ground movement estimation expression for any point outside excavation was established. And a zone chart of environmental impact partitions was put forward. These works make design of Beijing subway station deep foundation pit based on deformation control possible.(4) A deep beam model was established to investigate stress and deflection of building wall subjected to differential ground surface settlement. Proposed the triangular loads cantilever calculation model and computational model of simply supported uniformly distributed loads. This model can better simulate the stress and deformation conditions of built. it can provide evidence for deformation control standards.(5) Proposed a design and construction system of Beijing subway station excavation based on deformation control. The deformation control theory is the design of bolting system whith must make sure itself and the environment safety and normal use. Draw a series design reference about the supporting system stiffness and deformation of different position outside the pit.