The Mechanism Analysis And Control Of Ground Movements Induced By Subway Shield Tunneling Construction

Based on current progress of research and existent problems of study on ground movements caused by shield tunneling construction in metro tunnels in the world, the influence factors of ground movements induced by subway shield tunneling construction and the disadvantages of existing numerical simulation method of subway shield tunneling construction have been analyzed in detail. The scientific problem on the mechanism analysis, the law of deformation and the control technology of ground movements induced by subway shield tunneling construction is studied systematically. And it provides the scientific theory basis for the design and construction of tunneling engineering and solution the corresponding engineering damage environment problem.1. The mechanism of ground movements induced by subway shield tunneling construction is composed of the change of ground initial stress state and the consolidation and secondary consolidation deformation of soil around the tunnel caused by the construction disturbance. The root is the ground loss induced by construction, thus in the process of shield machine advancing, the ground movements show three-dimensional proliferation distribution by the shield machine as the central.2. According to establishing a numerical simulation model, a three-dimensional numerical simulation method which can reflect all of influence factors comprehensively is proposed to simulate the material and load of shield tunneling construction , and to carry out non-tensile stress analysis processing .The mechanism of ground movements and ground surface settlement induced by subway shield tunneling construction , the ground movements of small space and bi-orifice tunnel and the separation technology have been analyzed and researched deeply. The characteristics and laws of ground movements induced by subway shield tunneling construction are developed.3. Due to the influence factors of ground movements induced by subway shield tunneling construction, systematic research on the quantification degree of each influence of ground movements induced by subway shield tunneling construction on the condition of unequal ground loss ratio is canied out. Outer diameter of the shield, strata characterization (especially the internal friction angle of soil isφ,the lateral pressure coefficient of soil is k₀) and pressure of grouting and so on are the most sensitive and the most main influence factors of ground movements and ground surface settlement. The thickness of over-buried layer, the cohesion of soil c and the charge ratio of grouting at the end of shield machine are the major influence factors to ground movements and ground surface settlement. And other factors are secondary influence factors.Finally, a calculation model is established that makes the ground loss caused by metro tunnel excavating concentrated on a horizontal line that crosses the center of the tunnel. This model can reflect the effect of different relative bury and shape of cross-section tunneling to the ground surface settlement by citing a non-dimensional coefficientβ. On the basis of this model, the 2-D and 3-D corrected Peck formulas which are used to calculate and predict the ground movements caused by the tunnel excavation are reasoned out.