Joint bearing mechanism of structure and foundation for gravity anchor block of suspension bridge
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摘要: 基于普宣高速公路宣威岸重力式锚碇工程, 设计了不回填无预应力、不回填有预应力和回填有预应力3种计算工况, 利用数值仿真试验分析了重力式锚碇和地基的力学机制和破坏模式。承载机制表明: 8倍设计荷载之前没有塑性变形, 为弹性工作状态, 最大变形在锚岩界面, 摩擦效应居主导, 基底拉应力区可控, 锚碇结构抗滑移和抗倾覆性均处于稳定可控状态; 12倍设计荷载之后塑性区逐步扩展, 达到20倍设计荷载时全部贯通, 基底塑性变形明显, 锚碇结构变形显著, 基底夹持岩体剪切破坏, 夹持效应居主导, 基底拉应力区不可控, 锚碇结构抗滑移和抗倾覆性均处于不可控状态; 锚碇施加的预应力只在结构-岩基协调变形之前起作用, 之后影响不大; 回填可以极大地改善基底应力状态与结构扭转变形、抗滑移和抗倾覆稳定性, 可在容许变形范围内适当考虑增强效应。可见, 重力式锚碇结构-地基协调变形与联合承载机制, 表现为摩擦效应、夹持效应和回填效应的综合作用。监测结果显示: 通过基底拉应力和压应力监控结构与地基接触面安全性, 监测值小于地基容许承载力3MPa; 通过基底变位和地基深部水平位移监控结构抗滑移稳定性, 实际工程监测值小于1mm; 通过角点不均匀沉降监控锚碇抗倾覆稳定性, 倾斜值小于0.006;通过大体积混凝土温控监测可知, 内部最高温度小于60℃, 进出水温差小于15℃, 内表温差小于20℃, 峰后降温速率小于3℃·d-1; 锚束锁固荷载监测变化幅值不超过设计值的5%。Abstract: Based on the gravity anchor block engineering in Xuanwei Bank of Puxuan Highway, three kinds of computing schemes such as no backfilling & no pretension, no backfilling & pretension and backfilling & pretension were designed, and the mechanical mechanisms and fail modes of gravity anchor block and foundation were analyzed on basis of numerical test.Bearing mechanism presents that when the loads are less than 8 times of design load, plastic deformationcan't occur, the working situation is elastic, the maximum of deformation locates on the interface of structure and foundation, the friction effect is dominant, the tensile stress zone under foundation is controllable, and the anti-slipping and anti-overturning stability of anchor block is stable or controllable.When the loads are larger than 12 times of design load, the plastic zone expands step by step, and until to 20 times of design load, the plastic zone is cut-through.The plastic strain under the structure and the structure deformation of anchor block aspect are observable.The rock mass clamped by structure is broken.The clamping effect is dominant.The tensile stress zone under foundation is uncontrollable.The anti-slipping and anti-overturning stability of anchor block is unstable or uncontrollable.The prestress of anchor block acts only before the compatible deformation of structure and foundation, and the action fades away after the compatible deformation.Backfilling can greatly improves foundation's stress state and structure's torsional deflection, anti-slipping and anti-overturning stability, so the enhancement effect can be considered within the scope of allowable deformation.The joint deformation and bearing mechanisms of gravity anchor block and foundation are comprehensively performed by friction effect, clamping effect and backfilling effect.Monitoring result denotes that the interface safety of anchor block and foundation can be controlled by monitoring the tensile and compressive stress of base bottom, and the monitoring data are less than 3 MPa that is allowable bearing capacity of foundation.The anti-slipping stability of the structure is monitored by using the deflection and the deeply horizontal displacement of foundation, and the practical monitoring values are less than 1 mm.The anti-overturning stability of structure is monitored by using the uneven sedimentation of structure corners, and the inclined value is less than 0.006.The inner maximum monitored temperature of mass concrete is less than 60℃, the temperature difference of input and output water is less than 15 ℃, the temperature difference of anchor block's inner and surface is less than 20℃, and the post-peak cooling rate is less than 3 ℃·d-1.The changing amplitudes of stresses of anchor cables are less than 5% of design stress.
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Key words:
- suspension bridge /
- gravity anchor block /
- deformation mechanism /
- fail mode /
- joint bearing mechanism
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图 14 轴线剖面塑性区扩展与加载关系曲线
Figure 14. Relation curve of plastic zone expansion and load for axis section
图 15 重力式锚碇极限状态塑性区
Figure 15. Plastic zones of gravity anchor block under ultimate bearing condition
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