Controlling the risk of sinkholes over EPB driven tunnels - a client perspective

The occurrence of occasional sinkholes or very large settlements over EPB driven tunnels has been documented on a number of projects. Primary responsibility for avoiding sinkholes must lie with the tunnelling contractor, and the shield manufacturer. Almost all of the documented cases can be ascribed directly to failures in the planning, procedures, operation and maintenance of the machine, or to the design of the machine. However, the client has a major stake in controlling this risk. Sinkholes in urban areas are likely to lead to damage to roads and utilities, may damage buildings, and pose a risk to the public. It is current experience that simply appointing an experienced tunnelling contractor and requiring experienced operators are inadequate to control the risk of sinkholes occurring. A client can help to control the risk by providing sufficient site investigation, developing specifications that set minimum standards, and appointing experienced site supervision teams.