Calculation method and application of internal force of anchor pile based on "three-stage method"
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摘要: 针对抗滑桩常因地质条件、地形地貌等原因导致受荷段底面与嵌固段顶面不在同一水平面的情况，将此段划为次受荷段，并推导了次受荷段桩后设计荷载大小计算公式和荷载分布公式，以及在弹性地基梁和悬臂梁模型下的适用于悬臂桩和锚索桩内力与挠度计算通用公式。以巴东县焦家湾移民安置点库岸防护工程预应力锚索桩为例，研究次受荷段对抗滑桩内力和挠度影响。结果表明：忽略次受荷段后土压力作用的传统计算方法会使桩身弯矩计算结果偏小，导致桩身配筋量不足，存在设计安全隐患。再以锚索排数、位置为控制变量，研究其对预应力锚索桩内力和挠度的影响，提出预应力锚索可有效地降低抗滑桩工程造价；增加预应力锚索的排数有利于调节抗滑桩内力分布，设计时应优先考虑将锚索设置为多排锚索。Abstract: In view of the fact that the bottom surface of the loaded section and the top surface of the embedded section are not in the same horizontal plane due to geological conditions, topography and other reasons, this paper classifies this section as a secondary load section and derives the formula of designed load calculation and distribution about this secondary load section. As well as general formulas for the calculation of internal force, deflection of cantilever piles, anchor cable piles under elastic foundation beam and cantilever beam models. Taking the prestressed anchor piles of the reservoir bank protection project at Jiaojiawan resettlement site in Badong County as an example, the influence of the internal force and deflection of the anti-slide piles in the secondary load section is studied. The results show that the traditional calculation method that ignoring the effect of the earth pressure after the secondary load will make the calculation result of the pile bending moment smaller and leads to insufficient reinforcement of the pile, which really has a safety risk. Taking the number and position of the anchor cables as the control variables, the influence on the internal force and deflection of the prestressed anchor cables is studied, and it is proposed that the prestressed anchor cables can effectively reduce the construction cost of anti-slide piles; increasing the number of prestressed anchor cables which is beneficial to adjust the internal force distribution of anti-slide piles, and multi-row anchor cables should be given priority in the design.
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Key words:
- residual sliding force /
- secondary load section /
- design load /
- deflection /
- anchor pile design
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图 1 秭归县某家属楼区域剖面图
Qml.人工堆积；Qdel.滑坡堆积；J3p.上侏罗统蓬莱镇组
Figure 1. A sectional view of a family building in Zigui County
图 2 “三段法”划分示意图(据文献[15]修改，2018)
h1, h2, h3分别为主受荷段、次受荷段和嵌固段高度(m)；F1(θ1)，F2(θ2)，F3(θ3)分别为集中力1, 2, 3(kN)，其中θ1，θ2，θ3分别为集中力F1，F2，F3的倾角(°)；L1，L2，L3分别为集中力1, 2, 3到桩顶的距离(m)
Figure 2. Three-segment division diagram
图 3 次受荷段设计荷载计算示意图
h1, h2分别为主、次受荷段长度(m)；β1，β2分别为地面、滑面与水平面夹角；φ2为次受荷段岩土体内摩擦角；P为抗滑桩次受荷段支档力，大小等同于次受荷段桩后设计荷载(kN/m)
Figure 3. Schematic diagram of design load calculation for secondary load section
图 4 抗滑桩设计荷载分布示意图
A.荷载分布为三角形；B.荷载分布为矩形；C.荷载分布为梯形
Figure 4. Schematic diagram of design load distribution of anti-slide piles
图 7 不同计算方法的剪力图(a)和弯矩图(b)比较
Figure 7. Comparison of shearing force diagram (a) and torque diagram (b) of different calculation method
图 8 单排锚索不同位置的剪力图(a)和弯矩图(b)对比
Figure 8. Comparison of shearing force diagram (a) and torque diagram (b) of different position of single-row anchor cable
图 9 双排锚索不同位置的剪力图(a)和弯矩图(b)对比
Figure 9. Comparison of shear diagram (a) and torque diagram (b) of different position of double-row anchors cable
图 10 不同锚索排数的剪力图(a)和弯矩图(b)对比
Figure 10. Comparison of shear diagram (a) and torque diagram (b) different row number of anchor cable
表 1 岩土物理力学参数
Table 1. Geotechnical physical and mechanical parameters
岩土名称 重度γ/(kN·m-3) 黏聚力c/kPa 内摩擦角φ/(°) 天然 饱和 天然 饱和 天然 饱和 碎石夹土 22.0 22.5 13.0 11.0 22.0 20.0 强风化粉砂质泥岩 26.0 26.5 250.0 200.0 35.0 33.0 弱风化粉砂质泥岩 26.6 27.0 450.0 350.0 38.0 36.0 
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表 2 设计荷载取值
Table 2. Design load value
计算方法 剩余下滑力/(kN·m-1) 主动土压力/(kN·m-1) 设计荷载/(kN·m-1) “三段法” 1 664.72 1 491.05 1 664.72 “二段法1” 1 664.72 — 1 664.72 “二段法2” — 1 917.31 1 917.31
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表 3 锚索拉力值
Table 3. Anchor pull value
锚索排数 位置/m 锚索拉力/kN 单排 0.5 4 355.81 3.5 4 495.10 6.5 4 573.71 双排 0.5，3.5 1 557.68，2 197.29 0.5，6.5 1 100.41，3 061.97 3.5，6.5 1 430.37，2 836.38 三排 0.5，3.5，6.5 855.46，1 139.05，1 978.99
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