Monitoring Method and System of Pre-Convergence Deformation of Soft Surrounding Rock Tunnel

The prediction and early warning of tunnel collapse in weak surrounding rock is very important for tunnel construction safety, but the current monitoring methods are insufficient. In view of the shortcomings of existing monitoring methods for deformation of advanced core soil, a monitoring method of pre-convergence deformation of advanced core soil in front of the tunnel face was proposed; this involves placing an array displacement meter (ADME) in a leading small conduit and monitoring the deformation of the leading small conduit. The coupling accuracy test data of the ADME and steel pipe were combined to prove the feasibility of the device and test method. Finally, it is proposed to place the ADME in the lead duct, calculate the displacement of the measuring unit through the change of gravity and angle, and obtain the pre-convergence deformation of the lead core soil in front of the palm face. The results show that the floating error of the measuring unit of the ADME is 0.2 mm by calibrating the precision measuring device designed by itself. The absolute error is 0.2 mm @ 1 m. When the ADME is used for deformation measurement with displacement greater than 2 mm @ 1 m, the relative error can be controlled within 10%. Through the above deformation monitoring system, it is expected to realize a real-time monitoring method which can ensure monitoring accuracy and frequency, reduce interference to tunnel construction, and improve the safety and accuracy of tunnel construction in weak surrounding rock.