基于上限定理确定隧道式锚碇极限抗拔承载力

Determination of ultimate uplift capacity of tunnel-type anchorage based on upper bound theorem

隧道式锚碇作为一种新型的悬索桥锚碇结构,因具有因地制宜、经济环保的优点在多山的西南地区得到了广泛应用。已有研究表明,锚塞体围岩性质较差、埋深较浅,锚塞体与围岩接触界面结合程度较好的隧道式锚碇极易发生倒楔形冲切破坏。将破坏体视为以锚塞体中心线为轴线的旋转楔形体,假定破坏面为最小旋转曲面,利用变分法经典欧拉方程求解破坏体最小旋转曲面问题,确定旋转曲面母线方程;基于改进的Mohr-Coulomb强度准则,由主缆拉拔荷载和楔形体自重所做的外功率与楔形体沿滑移面所消耗的内功率相等的条件建立虚功方程,推导隧道式锚碇极限抗拔承载力上限解。开展隧道式锚碇室内模型试验,研究了拉拔承载过程中的坡面位移的变化规律及隧道式锚碇的破坏模式。研究结果表明,拉拔作用点的荷载-位移曲线可分为4个阶段:克服重力阶段、弹性阶段、弹塑性阶段以及破坏阶段;隧道式锚碇破坏模式为围岩倒楔形冲切破坏,破坏体可近似视为以锚塞体中心线为轴线的旋转楔形体;由推导公式得到的隧道式锚碇极限抗拔承载力计算值与实测值一致性较好,具有一定的可靠性,可为隧道式锚碇的设计提供参考。

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.