Research On Model Test Of Global Mechanical Properties Of Pipe-Poof Structure

As a safe and high efficient pre-supporting technology in the construction of underground engineering,pipe-roof method has significant advantages in the urban shallow buried tunnel engineering with large section.The pipe-roof pre-supporting structure is consisted of longitudinal pipes and transverse connections,and the interaction of longitudinal and transverse properties forms a whole.By taking pipe-roof method in shallow-buried underground excavated tunnels as the research object,research on model test of global mechanical properties of pipe-roof structure was carried out,and a series of results were obtained.1.Based on the Winkler elastic foundation beam theory,force analysis model of pipe-roof structure was established,and similar model test was made.The comparison and analysis of the results of force model and test indicate that the theoretical calculation model of combining simply supported beam and Winkler elastic foundation beam can better reflect deformation and stress characteristics of pipe-roof structure.2.According to the similitude theory,model similarity of pipe-roof test was obtained.And PMMA was chose as model material,the mixed soil,which uses undisturbed soil as aggregate,assisted by barite,fine sand,calcium carbonate and bentonite,was chose as model soil,a better test effect had achieved.3.Considering transverse connection of pipe-roof tunnel model,a new tunnel model,which has the same structure as the prototype tunnel,was designed,and the integrity problem of stress and deformation of test model can be successfully solved.4.The similarity model test of pipe-roof was carried out and the results indicate that the longitudinal influence range of the formation in front of working face is about2 times of excavation height.Moreover,under the support function of pipe-roof,optimum value of the excavation footage exists in the construction of underground excavated tunnels.In addition,the settlement of suppressing pipe-roof and ground-surface is not obvious by changing the spacing of the pipe-roof.While the bottom pipe-roof have a significant effect on the integral settlement of formation andpipe-roof transverse connection can better restrain pipe-roof global deformation in a certain extent.