Chemical injection application at tunnel service shaft to prevent ground settlement induced by groundwater drainage: A case study

Chemical injections are used in a variety of applications in civil and mining engineering, including ground stabilization, support anchoring, strata sealing, reduction and diversion of groundwater flow and water ingress, and creation of a load-bearing ring during tunneling. Historically, injection application without pressure was first employed by the Romans. Polyurethane injections have been used in coal mines to stabilize roofs and to reduce problems regarding water ingress in shafts and tunnels. This paper focuses on chemical injection, which was employed to prevent ground settlement induced by groundwater drainage from the shaft. As a result of the drainage of 4.5 l/s groundwater from the Shaft 4, which was sunk for service at Guzelyali station of Izmir Metro Project, the groundwater level dropped 4 m from the original level, and ground settlement reached 98 mm, while the inner tunnel vertical convergence was 23 mm. This can be explained with the closure of pore volumes in the overburden. Ground settlement was stopped and groundwater level approached its original level after chemical injection.