Experimental Research on the Transverse Effective Bending Rigidity of Shield Tunnels

What is it about?

The uniform rigidity ring model is commonly used to design the segmented structures of shield tunnels. However, model tests havebeenprimarilyusedtostudythetransverseeffectiverigidityratioηwithaconcentratedforce,whichisnotablydifferentfrom realisticloadingpatterns.Toobtainmorereasonableηvalues,inthisstudy,testswereperformedwithaconcentratedloadonan experimental bench and with a realistic loading pattern in sandy soil in a rigid steel tank. Three types of segmental ring models were designed and tested: straight-jointed, stagger-jointed, and uniform rings. The test results indicated that the η values of the stagger-jointedassemblymodewereclearlylargerthanthoseofthestraight-jointedassemblymodeunderbothloadingpatterns.η increased as the load increased under the realistic loading conditions, whereas η decreased as the load increased under the concentratedload.Moreimportantly,theηvaluesderivedfromtherealisticloadtestswereconsiderablylargerthanthosederived fromtheconcentratedloadtestsforbothassemblymodes(i.e.,0.423–0.672and0.587–0.761forthestraight-jointedandstaggerjointed assembly modes, respectively), and the former should be recommended for practical engineering applications. Furthermore, formulas relating η to the ratio of the cover depth to the tunnel diameter were proposed for sandy soil.

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Photo by Guillaume Bolduc on Unsplash

Photo by Guillaume Bolduc on Unsplash

Why is it important?

The uniform rigidity ring model is commonly used to design the segmented structures of shield tunnels. However, model tests havebeenprimarilyusedtostudythetransverseeffectiverigidityratioηwithaconcentratedforce,whichisnotablydifferentfrom realisticloadingpatterns.Toobtainmorereasonableηvalues,inthisstudy,testswereperformedwithaconcentratedloadonan experimental bench and with a realistic loading pattern in sandy soil in a rigid steel tank. Three types of segmental ring models were designed and tested: straight-jointed, stagger-jointed, and uniform rings. The test results indicated that the η values of the stagger-jointedassemblymodewereclearlylargerthanthoseofthestraight-jointedassemblymodeunderbothloadingpatterns.η increased as the load increased under the realistic loading conditions, whereas η decreased as the load increased under the concentratedload.Moreimportantly,theηvaluesderivedfromtherealisticloadtestswereconsiderablylargerthanthosederived fromtheconcentratedloadtestsforbothassemblymodes(i.e.,0.423–0.672and0.587–0.761forthestraight-jointedandstaggerjointed assembly modes, respectively), and the former should be recommended for practical engineering applications. Furthermore, formulas relating η to the ratio of the cover depth to the tunnel diameter were proposed for sandy soil.