Causes for and Treatment of Ground Surface Collapse in Construction of an Urban Traffic Tunnel

The causes for the ground surface collapse in the construction of an urban traffic tunnel are analyzed and the influence of the utility pipelines on the ground surface grouting is expounded.The following measures are taken to ensure the safe and successful tunneling through the collapse area: 1) Grouting and water sealing technologies,including water-stopping curtain with triple-fluid jet grouting columns,triple-fluid jet grouting within the curtain and horizontal jet grouting from inside the tunnel,are adopted.2) Due to the fact that the sandy cobble ground is subject to collapse in case of water,dewatering by means of ground surface dewatering wells and horizontal dewatering boreholes inside the tunnel are made so as to ensure that the tunnel excavation can be executed in dry condition.3) 4-step CRD method is adopted so as to control the tunnel deformation.In the end,safe tunneling is ensured.