Mechanical Mechanism of Slopes Stabilized with Anti-Slide Piles and Prestressed Anchor Cable Frame Beams under Seismic Loading
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摘要:
为了解抗滑桩—预应力锚索框架组合结构在地震作用下的受力机制，基于四川省东北部某滑坡治理工程，采用MIDAS/GTS有限元程序建立抗滑桩—预应力锚索框架数值模型，利用位移时程曲线法对加固边坡进行稳定安全系数计算，而后输入不同峰值地震加速度（peak ground accelerations，PGA）的Wolong地震波，分析了加固边坡的加速度响应、桩锚结构内力变化以及荷载分担规律.研究结果表明，加固边坡的稳定安全系数满足规范要求，在地震作用下其上部存在潜在浅层滑面，中部和下部存在潜在深层滑面，与静力条件下加固边坡的潜在滑面分布不同，这是加速度高程放大效应所致；随着输入地震波PGA增大，加速度高程放大效应明显加强，且抗滑桩桩身弯矩和剪力增大，但其最大值出现位置不变，桩身正、负弯矩最大值分别位于距桩顶约0.7L和0.4L处，最大正、负剪力分别位于距桩顶约0.9L和0.7L处，实际工程中需注意防范抗滑桩在滑面附近发生破坏；同时随着输入地震波PGA增大，桩锚承担的荷载逐渐增大，但抗滑桩分担的下滑力比例增大，而锚索分担的下滑力比例减小，故实际工程设计中不应固定桩锚荷载分担比例.
Abstract:A numerical model of a landslide stabilized with anti-slide piles and anchor cable frame beams was developed using a three-dimensional finite element program MIDAS/GTS. The factor of safety of the reinforced slope was calculated using the displacement time curve method. The acceleration responses, structural internal forces, and load-sharing rules were analyzed by inputting Wolong seismic waves with different peak ground accelerations(PGA). The results show that the factor of safety of the reinforced slope satisfies the code requirements. A potential shallow slip surface exists in the upper part of the slope, and a potential deep slip surface exists in the middle and lower parts of the slope under the earthquake action. The acceleration of the reinforced slope under seismic loading shows an elevation amplification effect. As the PGA of the input seismic wave increases, the amplification effect is enhanced. The bending moments and shear forces of the anti-slip pile increase when the PGA of the input seismic wave increases. The maximum positive and negative bending moments of the anti-slip pile are located at about 0.7 L(pile length) and 0.4 L from the top of the pile, respectively. The maximum positive and negative shear forces are located at about 0.9 L and 0.7 L from the top of the pile, respectively. When the PGA increases, the load sheared by piles and anchor cables increases gradually. However, the proportion of thrust shared by anti-slip piles increases while the proportion of thrust shared by anchor cables decreases. Thus, the variation of the proportion of thrust shared by anti-slip piles and anchor cables is recommended to be considered in engineering projects.
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Key words:
- anti-slide pile /
- prestressed anchor cable /
- slope /
- earthquake /
- mechanical mechanism /
- engineering geology
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图 6 监测点位移时程曲线图
a.折减系数k = 1.17时各监测点位移时程曲线；b.折减系数k = 1.18时各监测点位移时程曲线
Fig. 6. Monitoring point displacement versus time
图 7 地震作用下边坡等效塑性应变云图
k = 1.18，t = 50 s，PGA = 0.10 g
Fig. 7. Equivalent plastic strain contour of the slope
图 10 抗滑桩弯矩时程曲线(深度25 m处)
Fig. 10. Bending moment of anti⁃slip pile versus time(at 25 m depth)
图 11 不同PGA下抗滑桩的内力变化
a.弯矩图；b.剪力图；t=50 s
Fig. 11. Internal forces of anti-slip piles for different PGAs(t = 50 s)
图 12 不同PGA下锚索最大轴力变化(t = 50 s)
Fig. 12. Maximum axial forces of anchor cables for different PGAs(t = 50 s)
图 13 地震作用后加固边坡的等效塑性应变云图
PGA = 0.20 g，t = 50 s，k = 1
Fig. 13. Equivalent plastic strain contour of the reinforced slope
图 14 抗滑桩和锚索框架荷载分担示意图
Fig. 14. Schematic diagram of load sharing between anti⁃slip piles and anchor cables
图 15 不同PGA下桩锚荷载的分担比(t = 50 s)
Fig. 15. Proportion of load shared by anti⁃slip piles and anchor cables for different PGAs(t = 50 s) $ {F}_{c}=\frac{1}{S}\sum \left[{T}_{{i}_{2}}+{T}_{{i}_{1}}\mathrm{t}\mathrm{a}\mathrm{n}\phi \right] $, (6)
表 1 边坡岩土体计算参数
Table 1. Parameters of the slope materials
材料 重度$ \gamma $(kN•m-3) 弹性模量E(MPa) 泊松比υ 内摩擦角φ(º) 粘聚力c(kPa) 含碎石粉质粘土 19 24 0.35 15.5 23 强风化泥质页岩 21 65 0.3 19 46 中风化泥质页岩 23.5 450 0.25 29 120 中风化粉砂质页岩 23.5 1 800 0.25 35 298 
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表 2 抗滑桩单元计算参数
Table 2. Parameters of the anti⁃slide piles
材料 重度$ \gamma $(kN•m3) 弹性模量E(MPa) 泊松比υ 法向接触刚度En(MPa) 切向接触刚度Et(MPa) 抗滑桩 24 30 000 0.2 1 800 200
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表 3 锚索单元计算参数
Table 3. Parameters of the anchor cables
材料 重度$ \gamma $(kN•m3) 弹性模量E(MPa) 泊松比υ 灌浆长度(m) 未灌浆长度(m) 预应力值(kN) 锚索 78 195 000 0.2 8 27~52 400
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表 4 Rayleigh阻尼参数
Table 4. Parameters of Rayleigh damping
阻尼类型 质量参与系数α 刚度阻尼系数β 第一主振型周期T1(s) 第二主振型周期T2(s) 瑞利阻尼 1.47 0.04 1.28 0.85
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