Improved calculation of the rigidity of double-row piles and double-beam composite support and displacement analysis under different soil properties
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摘要:
双排桩支护组合体系作为一种新型悬臂类支护结构，其整体刚度的提升有利于保持基坑边侧的安全稳定。本文依托于张家口万全区某双排桩基坑支护工程案例，以现有双排桩冠梁刚度系数计算方法为基础，引入冠梁与连梁作用效应系数优化改进考虑连梁和冠梁作用的基坑矩形双排桩支护结构横向支撑刚度的计算方法，并对双梁组合支护体系下不同土性对双排桩前后排桩桩身最大横向位移的影响进行探讨。结果显示：（1）在双排桩结构计算中需考虑冠梁与连梁对双排支护桩的共同横向约束作用，并将冠梁与连梁的刚性连接作为一个整体以提高矩形双排桩双梁横向支撑刚度系数。（2）双梁组合支护体系组合刚度对桩顶位移有较大影响，组合刚度为40～50 MN/m下的位移与观测值较为贴近；冠梁计算长度与引入的冠梁与连梁作用效应系数对双梁组合支护体系组合刚度影响较大，计算长度对组合刚度呈负相关，效应系数对组合刚度呈正相关。（3）双梁组合支护体系下双排桩横向支撑刚度受前后排桩竖向与横向位移差影响，前后排桩桩身最大横向位移受土层内摩擦角、黏聚力和土体水平抗力比例系数影响；改变抗拉强度不会影响双排桩桩体位移。在基坑埋深以下及桩底范围内桩身存在位移拐点，拐点处各不同内摩擦角、不同黏聚力条件下位移相等。
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关键词:
- 双排支护桩 /
- 双梁横向支撑刚度 /
- 双梁组合作用效应 /
- 土体水平抗力比例系数
Abstract:As a new type of cantilever-type supporting structure, the double-row pile supporting combination system can improve the overall rigidity to maintain the safety and stability of the side of the foundation pit. The case of a double-row pile foundation pit support project in the Wanquan District of Zhangjiakou is taken as an example. Based on the existing double-row pile crown beam stiffness coefficient calculation method, the effect coefficient of the crown beam and the coupling beam is introduced to optimize and improve the effect of the coupling beam and the crown beam. The results show that (1) in the calculation of the double-row pile structure, the common lateral restraint effect of the crown beam and the connecting beam on the double-row supporting piles should be considered, and the rigid connection of the crown beam and the connecting beam should be taken as a whole to improve the rigidity coefficient of the double beam lateral support of a rectangular double-row pile. (2) The combined stiffness of the double-beam combined support system has a greater impact on the displacement of the pile top, and the displacement under a combined stiffness of 40～50 MN/m are close to the observed value. The calculated length of the crown beam and the introduced crown beam and connecting beam effect coefficient have a great influence on the combined stiffness of the double-beam composite support system. The combined stiffness decreases with the increase of the calculated length, and increases with the decrease of the effect coefficient. (3) The lateral support stiffness of the double-row piles under the double-beam composite support system is affected by the difference between the vertical and lateral displacements of the front and rear piles. The maximum lateral displacement of the front and rear piles is affected by the friction angle of the soil, the cohesion and the proportional coefficient of the horizontal resistance of the soil. Changing the tensile strength will not affect the displacement and deformation of the double-row piles. There is a displacement inflection point below the buried depth of the foundation pit and within the scope of the pile bottom. The displacement at the inflection point is equal under different friction angles and different cohesive forces.
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表 1 双排桩结构设计及计算参数
Table 1. Design and calculation parameters of the double-row pile structure
基坑深度H/m 15.200 前排桩冠梁 —— 嵌固深度/m 15.000 ├宽/m 0.800 桩截面类型 圆形 ├高/m 0.500 └桩直径/m 0.800 └刚度/(MN·m−1) 28.672 桩布置形式 矩形 后排桩冠梁 —— ├桩排距/m 1.600 ├宽/m 0.800 └桩间距/m 1.400 ├高/m 0.500 混凝土强度等级 C25 └刚度/(MN·m−1) 28.672 计算长度/m 85 双梁效应系数 0.85 连梁宽度/m 0.800 连梁高度/m 0.800 
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表 2 土层信息表
Table 2. Information of the soil layer
层号 土层
名称层厚/m 重度/
(kN·m−3)黏聚力/
kPa内摩擦
角/(°)压缩模量/
MPam法地基土
弹性抗力系数
/(MN·m−4)1 杂填土 1.19 16.0 0.00 0.00 10.000 0.00 2 粉土 3.70 15.5 15.50 22.00 22.000 9.03 3 细砂 1.70 18.0 0.00 32.00 6.300 17.28 4 黏性土 6.00 16.5 25.30 15.00 15.000 5.53 5 圆砾 0.80 20.0 0.00 38.00 35.000 25.08 6 黏性土 3.20 16.7 25.60 15.40 15.000 5.76 7 圆砾 20.00 20.0 0.00 38.00 35.000 25.08
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表 3 不同双梁组合刚度系数下双排桩桩顶横向位移
Table 3. Horizontal displacement of pile tops of double-row piles under different double-beam combination stiffness coefficients
双梁组合刚度系数/（MN·m−1） 20 30 40 50 60 桩顶横向位移/mm 13.8 10.3 8.5 7.1 4.6
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表 4 双梁组合支护体系下不同土性对排桩最大横向位移计算结果
Table 4. Calculation results of force and deformation of row piles with different soil properties under the double beam composite support system
计算参数 参数取值 前排桩身最大
横向位移/mm后排桩身最大
横向位移/mm土层内摩擦角φ/(°) φ-10° 8.43 9.18 φ 8.00 8.81 φ+10° 7.84 8.49 φ+20° 7.63 8.28 土层黏聚力c/kN 0.5c 8.38 9.24 c 8.00 8.81 5c 7.71 8.53 10c 7.68 8.49 土层抗拉强度σt/（104N） 0.5σt 8.12 8.91 σt 8.00 8.81 5σt 7.96 8.80 10σt 7.96 8.79 土层水平抗力
比例系数m/(MN·m−4)m-20 8.19 9.02 m 8.00 8.81 m+20 7.88 8.70 m+50 7.43 8.46
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