Abstract：Taking Dahuofang Water Transfer Project in Liaoning Province as background，the monitoring technique of tunnel clearance displacements in the tunnel boring machine(TBM) bid segments is introduced under condition of TBM construction. Based on the tests，a monitoring method of TBM tunnel clearance displacements with laser collimation is proposed. It comes true by utilizing the longitudinal intervisible space between the boring machine and tunnel profile and using the laser collimation method to the three measuring points on the crown and two sidewalls. Thereby，the problem that the tunnel clearance displacement under condition of TBM construction is difficult to be obtained with existing monitoring methods can be resolved. Also，the SWL–I tunnel laser displacement monitoring system with satisfying measuring precision，simple and easy-to-operate characteristics is developed. The system has been applied and verified in the construction of Dahuofang Water Transfer Project by use of Robbins and Wirth¢s open TBMs. The displacement characteristic curves of surrounding rock in the tunnel crown and both sidewalls at the end of the machine cutterhead are obtained firstly；and the monitoring of tunnel clearance displacements under condition of TBM construction has been realized.
