Study and Application of Construction Face Stability in Tunnel and Shaft Excavation Safety

According to the failure modes for tunnel construction face, this paper establishes the sliding body models in cylinder and wedge types. The applied forces on the two types are analyzed. Through the sliding body diagrams, the relationship among different factors is fined out, especially the safety factors of cylinder and wedge types are determined. The calculation of the vertical frictional force against the sliding body through the diagram analysis has special meanings. It means that the complex parameters are easy to obtain, and other parameters can be defined through simple calculations or according to the certain knowledge. When the safety factor drops to 1, the yield strength of the tunnel construction face is reached and the technical and practical treatment must be put into effect. Finally, the application of the sliding body diagrams is also discussed. It shows that the results of the diagrams, of the theoretical analysis and of the finite elements have essential identical conclusions. Of course, only through the analysis of the sliding body diagrams, the applied area is limited. For special conditions, the differences are too large to explain the immediate roof collapse. Therefore, the other suitable methods are also necessary.