Stability Study On Shield Tunnel Excavation Face In Water-rich And Complex Geological Condition Of Xuzhou

The instability of shield tunneling face means that when the shield machine cutter head support stress is lower than a certain value, the excavation face will cause horizontal catastrophe damage. The value is defined as the limit stress of the excavation face. This paper is relied on Pengcheng Square station to the Cultural Palace Station section of Xuzhou City Rail Transit Line 1, focusing on the shield tunnel excavation face stability by numerical calculation and theoretical calculation method.The main results are:(1)The limit support stress ratio can be more clearly defined by the.relationship between horizontal displacement of the excavation face and support stress ratio. The theoretical calculation results of the limit supporting stress ratio, applying 3D silo model and Terzaghi earth pressure theory, have a better fitting degree to the numerical calculation results.(2)The greater the friction angle is, the less the limit stress ratio will be, and the excavation face will be later to enter the state of instability.When the depth of the shield tunnel reaches a certain thickness(at least twice the diameter of the tunnel), the stress ratio of different buried depth is similar. The influence of the depth on the limit support stress ratio can be neglected.(3)The key parameters of ABAQUS based on total pore pressure analysis and variable pore pressure analysis method are discussed respectively. The theoretical calculation method is presented by using the 3D silo model and numerical water head distribution. The results are well fitted with the numerical results.(4)The existence of ground water has a negative effect on the stability of the excavation face. When the depth of the water level increases, the limit support stress will significantly reduce and the tolerance horizontal displacement of excavation face will be larger.A greater permeability coefficient is beneficial to the stability control of excavation face. The greater the permeability coefficient is, the less the limit support stress ratio will be.(5)Combined with Xuzhou city engineering geological conditions, the limit support stress in water rich silty sand layers is determined by ABAQUS variable orifice pressure analysis.The influence of excavation face stability on the ground surface settlement is analyzed, and the characteristics of stratum settlement curve with the change of depth are summarized, which provides a reasonable reference for theurban rail construction in Xuzhou.