Is A Full Face Drive Safer and More Effective Than Sequential Excavation in Mixed Ground?
It is necessary of some adequate instruments to stabilize the face and excavated tunnel wall when tunnelling passes through difficult ground. There are many authors who investigate the instruments (e.g., face bolts and canopies) to stabilize the face and excavated tunnel wall. But the horizontal surface was used in their models of the analyses. Cheung Shan Tunnel in Hong Kong passes through mixed ground at South Portal. The slope is cut by inclined angle of 45° and 70°. In this paper, FLAC3D is used to simulate the 3D model of tunnel excavation and investigate the impact of the inclined slope on the safety of two tunnelling methods under same geotechnical parameters, initial stresses, reinforcements and temporary supports. Numerical tests of the reinforcements are also done by FLAC 3D for properties of the reinforcements. Calculations of cycle time are used to compare face advance rate for the two tunnelling methods. Based on the results of the numerical analyses and calculations, the full face drive is safer and more effective than the sequential excavation in the mixed ground.