大跨径悬索桥隧道锚变位分析

四渡河大桥是我国首次采用隧道式锚碇的大跨径悬索桥。基于实测综合确定的岩体参数,用三维弹塑性有限元法对包括下部公路隧道施工、隧道锚开挖、浇注、预应力施加、挂缆等全部工序进行了模拟。围岩和锚体混凝土离散为8节点三维实体单元,隧道和锚碇的喷射混凝土及二次衬砌离散为4节点三维壳单元。围岩采用修正的Mohr-Coulomb破坏模型。围岩开挖应力的释放用场变量相关折减弹性摸量法模拟。研究结果表明,浇注锚体混凝土阶段顶部围岩最大下沉位移2.3 mm,底部围岩竖向位移趋近于0。在正常缆力下,两个锚体围岩的位移场有部分的独立性,缆力增大时两锚体围岩形成共同的位移场。锚碇可能的破坏形式是两锚体向外侧歪斜拔出;锚碇周围岩体的位移均处于毫米的量级,远小于桥塔顶部位移的容许值。数值分析的结果为该大桥的设计与建造提供了可靠依据。

ANALYSIS OF DISPLACEMENTS OF TUNNEL-TYPE ANCHORAGE FOR A LARGE-SPAN SUSPENSION BRIDGE

The tunnel-type anchorage of Siduhe Bridge is used for the first time in large-span suspension bridge in China.Based on the rockmass parameters from tests,the three-dimensional elastoplastic analysis has been performed to simulate the complete sequence of construction including highway tunnel excavation,tunnel-type anchorage excavation,concrete in-situ casting,prestressed concrete anchorage,main cable installation,etc..By using 8-node 3D brick elementst,he surrounding rockmass and concrete anchorage bodies are simulated.Shotcrete and lining are simulated by 4-node shell elements.A modified Mohr-Coulomb model is adopted for the rockmass.Stress relaxation in surrounding rock due to excavation is simulated by field-dependant deduct elastic modulus method.The maximum vertical displacement of the top rock is 2.3 mm and that of the bottom rock approximates zero after anchorage concrete being cast.The displacements of the surrounding rock are independent of each other under designed cable force;and the displacement field approaches to same when the cable being overloaded.The failure pattern is that two anchorage bodies are pulled out which decline outsides.The magnitude of displacements in the surrounding rock is graded in mm,which is far below the allowance value of displacement on tower top.The results of the numerical analysis are used in the design of the tunnel-type anchorage.