Determination of ultimate uplift capacity of tunnel-type anchorage based on upper bound theorem
As a new type of suspension bridge anchorage structure,tunnel anchorage has been widely used in southwest mountainous areas due to its advantages of local conditions,economic and environmental protection.Existing studies have shown that the tunnel anchorage with poor surrounding rock properties,shallow burial depth,and good contact interface between the anchor plug body and the surrounding rock is prone to inverted wedge punching failure.The failure body was regarded as a rotating wedge-shaped body with the center line of the anchor plug as the axis,and the failure surface was assumed to be the minimum surface of revolution.Then,the classical Euler equation of the variational method was used to solve the problem of the minimum surface of revolution of the failure body,and the generatrix equation of the surface of revolution was determined.Besides,based on the improved Mohr-Coulomb strength criterion,the virtual work equation was established under the condition that the external power generated by the main cable pulling load and the self-weight of the wedge body is equal to the internal power consumed by the wedge body along the slip plane.The upper bound solution of the ultimate uplift bearing capacity of the tunnel anchorage was derived.The indoor model test of tunnel anchorage was carried out,and the variation law of slope displacement and the failure mode of tunnel anchorage in the process of drawing and bearing were studied.The test results show that the load-displacement curve of the pull-out point can be divided into four stages:the overcoming gravity stage,the elastic stage,the elastic-plastic stage and the failure stage.The failure mode of tunnel anchorage is inverted wedge-shaped punching failure of surrounding rock,and the failure body can be approximated as a rotating wedge-shaped body with the centerline of the anchor plug as the axis.Furthermore,the calculated value of the ultimate pull-out bearing capacity of the tunnel-type anchorage obtained by the derived formula is in good agreement with the measured value,and has certain reliability,which can provide a reference for the design of the tunnel-type anchorage.
tunnel-type anchoragemodified Mohr-Coulomb strength criterionlimit analysis methodlaboratory model test
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