Mechanical Mechanism Of Piperoofs Revealed By The Pasternak Model Based On Variable Coefficient Of Subgrade Reaction

With the rapid development of urban infrastructure construction, construction oftunnels such as metros, underground streets is more and more common in the city. Withtunneling, it needs to effectively limit the sink of surface and vault, to maintain thestability of the excavation face. As a result, doing pre-support consolidation beforeexcavation is necessary. Pipe roof pre-support technology, as an important auxiliarymethod of tunnel excavation, due to its distinguished features such as long pre-supportdistance, short construction period, high reliability, it was widely applied to the tunnelconstruction. However its mechanical behavior and design details still have not beenresearched systematically. Until now, the application of this method is yet based on theexperience analogy of engineers, which is already unable to meet the need ofunderground project development. Consequently, it is very important to analyze thebehaviors of pipe shed supporting under different construction condition and geologicalcondition.According to the domestic and foreign knowledge on pipe roof pre-support design,the research was based from the following aspects: the design of the pipe roof, themechanical mechanism of pipe roof pre-support, and the numerical simulation of theactual project:(1)Based on the characteristic of pipe roof advanced support, the mechanicalmechanism, scope and design parameters of pipe roof were detailedly summarized.(2)The lode scope and calculation formula of pipe roof in the shallow tunnel wasdrawn according to the surrounding rock pressure theories of shallow tunnel. Based onPasternak elastic foundation beam theory and the mechanical model of pipe roofpre-support, the differential equations of corresponding deformations, turn angles,bending moments and shear were deduced. The mechanism action of the pipe roof wasbased on a detailed analysis, and put forward relevant parameter design method.(3) The tunnel face stability is assumed to be the three-dimensional slope stabilityproblem under cover loads, and derive the determination method for the stability oftunnel face. The reasonable proposals then put forward to ensure the tunnel safety.(4) Taking a shallow tunnel project for example, numerical simulation was carriedout by using program MIDAS/GTS. The compare between the on-support results andpipe-roof support results proved that the function of pipe roof in controlling thesettlement of surface and vault, maintain the stability of the excavation face wasobvious.