Study Onadvanced Support Technique Withpipe-roof Intunnel

Pipe roof pre-support technology, as an auxiliary technique in tunnel excavation, has important function on preventing tunnel collapse, restraining ground movement and controlling ground surface settlement. It can solve the tunnel excavating problem effectively when the tunnel is constructed in soft or weak strata, such as shallow buried, crashed soft surrounding rock and abundant underground water. Furthermore, Pipe Roof Method has been widely applied because it has long pre-reinforce distance, high reliability, short construction period and other relative advantages. Taking pipe roof pre-support technology as the object to be investigated, using theory analysis and numerical simulation, a series of results were obtained.(1) Pre-supports and protections mechanism of shed-pipe technology is explored. Considering with the effects of the tunnel cover depth, the geological conditions and manners of excavation on the surrounding rock pressure, the equations for pipe roof reinforcement loading were proposed according to Terzaghi theory. Considering the delay effect of initial lining, an analytical approach based on Winkler elastic foundation beam theory for pipe roof reinforcement was put forward. The analytical solution obtained the deflection of pipe roof supporting structure, corner and bending moment equation.(2) The design parameters of Pipe roof supporting structure are systematically summarized. Application of soil arching effect principle obtains the maximum allowed to pipe roof ring spacing of calculation formula.(3) Taking a tunnel engineering for example, 3-d finite difference numerical simulation software was used to simulate advanced pipe roof supporting structure. Scope of pipe roof length, support arrangement for the change, grouting thickness of tunnel excavation were investigated. The calculation results show that: when using fan-shaped symmetrical arrangement type, when central angle equal to 120 degrees, it is the best arrangement type. Shed-pipe grouting for tunnel displacement control also have more significant effect of the tunnel, up to 45%, the horizontal displacement control also reached to 30%. Don't shed-pipe grouting for tunnel vertical displacement control also have more significant effect of the tunnel, up to 30%, the horizontal displacement control also reached to 20%. The selection of the length of pipe roof supporting structure need combining geology condition of the strata and the precision of displacement control, then we can achieve economic and security purposes . When grouting thickness changes between 0.3 m to 0.6 m, the change of the tunnel grouting thickness is not significant for the control of the displacement. It shows that there is a value which causes the accuracy of the control of displacement and security and economic to obtain some balance , namely the best grouting thickness.Above research results for pipe roof supporting design theory and construction practice are of great significance.