Abstract: After the separation of the highway and railway in an underwater tunnel, varying spacing underpass disturbance and detachment between soilstructure occurred during a metro tunnel parallelly crossing an existing opencut tunnel. In this study, a case study is conducted on the metro tunnel on the north bank section of the Yellow rivercrossing tunnel in Jinan, China, and a refined threedimensional simulation model considering the detachable stratastructure interface and structural deformation joint is established to investigate the influence of shield tunneling on 〖HJ2.7mm〗stratumstructure detachment and the existing structure under various reinforcement schemes. The results reveal the following: (1) The maximum ground settlement is reduced by 52% and the peak superposition effect of the settlement curve is effectively controlled after the column pile reinforcement is adopted. (2) The maximum lateral differential settlement and the maximum settlement of the existing structure floor are reduced by 43.4% and 47.0%, respectively, during shield tunneling after using reinforcement of column pile and threeaxis mixing pile. (3) The maximum detachment between the tunnel floor and the soil due to shield tunneling is 1.44 mm without reinforcement. Compared with the reinforcement of threeaxis mixing pile, the reinforcement of column pile is more effective in reducing the detachment between the tunnel floor and the soil. (4) The maximum tensile stress increment of the existing structure without reinforcement measures exceeds the control limit, and the reinforcement of threeaxis mixing pile tends to increase the tensile stress increment within the grouting range of the existing structure, while the use of column pile combined with threeaxis mixing pile reinforcement can effectively reduce the tensile stress increment of the existing structure by 50%. When shield tunneling parallelly under existing structure, it is safer and more effective to take the ground displacement control (antidetachment) and structural stress control into consideration than to strengthen the single reinforcement measure.

Key words: metro shield tunnel, existing opencut highway tunnel, column pile, threeaxis mixing pile, stratumstructure detachment, structural deformation, stress increment