悬索桥隧道式锚碇夹持效应的试验研究

Experimental study of the clamping effect of the suspension bridge tunnel-type anchorage

隧道式锚碇的夹持效应机制及其破坏形态的研究尚不充分,不利于隧道式锚碇设计理论的优化。通过开展锚碇的二维室内模型试验,分析了锚碇和岩体联合承载的过程、机制及锚碇自岩体内拔出时的破坏形态,并针对锚碇的楔形角和埋深等几何要素对锚碇的承载力和破坏特征的影响做了简单分析,在一定程度上揭示了隧道式锚碇夹持效应的本质。所得结论主要有:(1)锚碇加速非线性移动挤压土体产生附加应力,激发夹持效应发挥抗力作用,调动周围岩土体联合承载。(2)隧道式锚碇的承载力由自重效应和夹持效应组成,自重效应不足以平衡主缆荷载时,夹持效应才发挥作用。从经济和安全角度,应对锚碇的体型进行合理设计,使得夹持效应得到有效发挥。(3)锚碇的楔形角影响锚碇的极限承载力,设计时应通过优化分析确定优势角。(4)锚碇的埋深越大,承载力越大,两者基本成线性关系。在实际工程中应把握施工难易性、经济性及承载力之间的关系综合确定埋深。(5)锚碇裂纹的产生和发展与锚碇及岩体的应力位移响应具有相关性。锚碇与土体相对静止时无裂纹产生,破坏形态基本形成的时间与锚碇加速非线性位移阶段相对应。

Studies on the clamping effect and failure mode of the tunnel-type anchorage are still insufficient,leading to many difficulties in the optimization of design philosophy of the tunnel-type anchorage.In this work,the bearing characteristics,bearing mechanics and the failure mode of the tunnel-type anchorage were analyzed through 2 D laboratory model tests.Besides,the influences of wedged angle and burial depth on the bearing capacity and failure mode were studied as well.This work reveals the essence of the clamping effect of the suspension bridge tunnel-type anchorage to some extent.Main conclusions are given as follow:First,additional stress is generated when the anchorage moves with a crescent accelerated velocity and squeezes the surrounding rock.The clamping effect results in resistance and the surrounding rock and soil start to bear the main cable load jointly.Second,the bearing capacity of the tunnel-type anchorage is contributed by gravity and the clamping effect.The clamping effect will play a role only when the gravity effect fails to balance the main cable load.From the view of economy and security,it is necessary to rationally design the size of the anchorage to ensure the role of the clamping effect.Third,the bearing capacity of the tunnel-type anchorage is also influenced by the wedged angle and it is necessary to optimize the wedged angle to obtain the maximum bearing capacity.Fourth,the bearing capacity of the tunnel-type anchorage increases linearly with the burial depth.Thus,in the actual project,the burial depth should be determined according to the bearing capacity,the construction difficulty,as well as economy.Finally,the initiation and propagation of the cracks is associated with the response of the stress and displacement.There is no crack initiation when the anchorage and surrounding rock are relatively static.The formation time of the failure mode corresponds to the nonlinear displacement stage of anchorage acceleration.