A case study of urban road subsidence induced by the underground connection of the shield tunnelling method

A case study of the road subsidence hazard that occurred during the construction of a cable tunnel was conducted. The cable tunnel was built 30 m below the ground surface by using the shield tunnelling method, parallel to a sewage pipe with a diameter of 2000 mm. During shield docking, the bolt of the seal plate in the shield segment ruptured. This rupture led to water flooding into tunnel and the settlement of the ground surface. The causes of the subsidence hazard were analysed and discussed. The results of this case study indicate that risk assessment and hazard analysis of shield tunnels should be conducted separately in the planning, design, and construction phases for ensuring disaster mitigation. To avoid the occurrence of a subsidence hazard, sensors should be embedded 30 m below the ground surface and near the shield machine. Using monitoring sensors and increasing the number of observed frequency are effective in enhancing the settlement sensitivity so as to provide early warning information. Ground improvement is suggested even while using the concentric interlace docking method.