地震作用下华丽高速公路金沙江桥华坪岸顺层边坡动力稳定性评价

Dynamic stability evaluation on Huaping bedding bank slope of Jinshajiang River Bridge in Huali Expressway under seismic action

以华丽金沙江桥华坪岸顺层边坡地震稳定问题为研究对象,在slide下利用Janbu-simplified法计算了其最不利滑动面和安全系数,为模型试验确定了宽900 m×高450 m的试验范围。采用拟静力法,在Phase 2D下利用有限元强度折减法模拟模型边坡,计算了0.00g、0.10g、0.15g、0.20g、0.25g、0.30g、0.35g等7个地震工况的安全系数和位移。对比不同工况下的安全系数、位移与水平地震加速度曲线,结果表明,(1)极限平衡法与强度折减法所得安全系数在1.0附近安全系数离散性最小,远离1.0则安全系数的离散性增大,差异是两类方法极限状态定义的不同造成的。基于安全系数确定的临界水平地震加速度为0.20g;(2)剪应变揭示的边坡破坏模式为桥墩位置拉剪破坏、T2凝灰岩主滑和前缘近于水平剪出破坏,坡体内部的变形响应敏感性为水平位移>竖向位移>剪应变。基于变形演化规律确定的临界值为0.15g^0.20g,相应水平位移预警值为10.2 mm,室内模型试验验证了上述分析的合理性;(3)综合确定华坪岸顺层边坡临界水平地震加速度为0.2g,50年超越概率为10%和100年超越概率为2%对应的安全系数分别约为1.2和1.1,华坪岸边坡在现行抗震设防标准下是安全的。当前选择安全系数作为边坡稳定性评价指标,而安全监控实践中一般选择可操作性和预警性强的变形值作为控制指标,所以边坡稳定性评价需要采取安全系数与临界位移相结合的方法。

Seismic stability of Huaping bedding slope of Jinshajiang River bridge in Huali Expressway is studied. Safety factor, slip surface and scope of width 900 m and height 450 m are suggested by Janbu-simplified method based on slide. Safety factors and deformations of seven kinds of seismic working conditions such as horizontal acceleration being 0.00 g, 0.10 g, 0.15 g, 0.20 g, 0.25 g, 0.30 g and 0.35 g are respectively computed by strength reduction method of finite elements on basis of Phase2 D using quasi-static method, simulated object being model test. After curves of safety factor or defromation and horizontal acceleration of different seismic load conditions are compared with each other. The results show that:(1) Safety factor near to 1.0, the deviation is least, otherwise the deviation and discreteness increase, which is caused by disunity of limit condition defined by the two methods. Critical horizontal acceleration done by safety factor is 0.20 g.(2) Fail mode presented by shear strain is bridge pier being tensile-shear fail, sliding in T2 tuff stratum and horizontally sheared out in front. Sensitivity order of deformation response in slope is horizontal displacement more sensitive than vertical displacement than shear strain. Limit value done by deformation evolution is 0.15 g-0.20 g, corresponding horizontal displacement being 10.2 mm. These are all proved by model test.(3) Finally, the critical horizontal acceleration of Huaping bedding slope comprehensively being 0.2 g, safety factors of exceedance probability being 10% for 50 years and that of exceedance probability being 2% for 100 years are respectively 1.2 and 1.1. Huaping slope is safe under current seismic fortification criterion. In practice, safety factor considered material strength reserve is often selected as evaluating indicator of slope stability; but a strong operability and warning displacement considered deformation mechanism is selected for engineering safety monitoring. So, slope stability needed to be estimated by safety factor combined with critical displacement.