摘要
盾构开挖易引起上覆地表沉降变形,进一步会引起上覆既有管线的受力变形响应.基于此,提出了一种盾构开挖引起上覆管线变形的简化计算方法.首先采用Loganathan公式获得既有管线在盾构下穿影响下的附加应力,进一步将管线简化成无限长梁放置在Pasternak地基上,引入无限远端侧向土体位移对既有管线的影响,采用力学平衡法获得管线竖向受力变形控制方程,通过有限差分法获得管线变形及其内力数值解析.案例分析表明:与退化解析对比,该方法计算结果更贴近既有文献工程实测数据,验证了其可靠性.进一步参数研究表明:增大隧道与管线的竖向净距会引起既有管线受力变形的非线性减小;管线变形及其内力会随着地层损失率增大而线性增大;管线抗弯刚度的增大会引起管线变形减小,但会大幅增加管线弯矩.
城市地下空间的不断开发带动了城市经济的飞速发展,市政管道的建设极大地便利了城市居民的生活.而在城市地下空间不免会出现邻近开挖对既有管线造成安全威
邻近开挖对既有管线影响的理论文献大部分都是基于两阶段法.第一阶段采用Loganathan
综上所述,Pasternak地基能够考虑到土体剪切变形影响,且较为简单,广泛应用于土与结构相互作用研究中.然而,很少有学者考虑到管线无限远端侧向土体对管-土相互作用的影响.基于此,本文将既有管线简化为无限长梁放置在Pasternak地基上,引入无限远端土体侧向位移对既有管线的影响,采用力学平衡法获得管线竖向受力变形控制方程,再通过有限差分法获得管线变形及其内力数值解析.该方法计算结果与工程实测数据接近,验证了该方法的可靠性.最后系统分析了隧道与管线竖向净距、地层损失率、管线抗弯刚度对既有管线受力变形的影响.
1 分析方法
1.1 自由位移场求解
基于文献[
(1) |
式中:ε为等效地层损失比;R为隧道开挖半径;H为隧道埋深;z为距地表垂直距离;x为管线到隧道中心线的水平距离;为土体泊松比.
根据冯国辉
(2) |
式中:为土体竖向变形曲率;kc为土体弹簧刚度,相当于Winkler地基模型弹簧参数;Gc为土体剪切层刚度.
对于Pasternak地基模型参数取值方面,林存刚
(3) |
(4) |
式中:D和EI分别为既有管线直径和抗弯刚度;Es为土体弹性模量;为土体泊松比;t为土体剪切层厚度,取t=2.5
1.2 管线变形理论分析
管线受到附加荷载产生沉降变形时,不仅受到管线下方土体的地基反力,其侧向土体也同样对管线的变形存在约束作用,如

(a) 管线与土体相互作用力学模型

(b) 侧向土体变形示意图
图1 侧向土体影响下管-土相互作用模型
Fig. 1 Pipeline-soil interaction considering the lateral soil effect
为了分析侧向土体作用对既有管线的影响,做出如下假定:
1) 半无限空间内的土体为均质土体,变形均在弹性范围内;
2) 侧向土体作用力T1与T2通过土体剪切层附加在管线两侧;
3) 假定管线为刚性管线,不考虑管线非线性变形,且管-土协调变形,两者无间隙.
对于任意x=x0的平面,管线侧向土体的变形平衡方程为:
(5) |
式中:为侧向土体剪切层沿y轴方向上的变形,通过解方程可得
(6) |
如
(7) |
进一步,侧向土体对管线的作用力为:
(8) |
考虑到管线受到的土体反力为:
(9) |
结合以上分析,在侧向土体力的约束作用下,管线变形控制方程为:
(10) |
综合式(
(11) |
考虑到

图2 既有管线差分简化图
Fig. 2 Simplified differential diagram of the existing pipeline
此时,
(12) |
那么管线弯矩和剪力可分别简化为:
(13) |
(14) |
由于实际管线两端可简化成自由状
(15) |
那么
(16) |
(17) |
(18) |
(19) |
(20) |
(21) |
至此,得到管线竖向变形w(x)位移的数值解析,将得到的结果代入
2 解析验证
文献[

图3 隧道与管线位置简图
Fig.3 Simplified location diagram between tunnel and pipeline
R/m | H/m | z0/m | ε0 /% | E0 /MPa | ν | D/m | EI/(kN· |
---|---|---|---|---|---|---|---|
3.0 | 14.4 | 8.7 | 0.84 | 8.2 | 0.3 | 3.0 |
5.87×1 |

图4 管线变形计算结果与实际工程数据对比曲线
Fig.4 Comparison of the calculated and actual project results of deformation of tunnel
3 敏感参数分析
考虑到隧道-管线竖向净距、地层损失率及管线抗弯刚度对管-土相互作用的影响,假设隧道轴线和管线轴线垂直相交,其余参数见
R/m | H/m | z/m | ε/% | ES/MPa | ν | D/m | EI/(N· |
---|---|---|---|---|---|---|---|
3.0 | 15 | 8 | 1 | 20 | 0.3 | 3.0 |
3.36×1 |
3.1 隧道-管线竖向净距d
不同隧道-管线竖向净距d下盾构下穿引起既有管线变形及其弯矩变化如

(a) 位移

(b) 弯矩
图5 隧道-管线竖向净距变化对管-土相互作用影响
Fig. 5 The influence of pipeline-soil interaction with the
variation of tunnel-pipeline vertical distance
3.2 地层损失率ε
不同地层损失率ε下既有管线受到盾构下穿影响产生的最大位移和弯矩见

(a) 位移

(b) 弯矩
图6 地层损失率变化对管-土相互作用影响
Fig.6 The influence of pipeline-soil interaction with the
variation of volume loss
3.3 管线抗弯刚度(EI)new
不同管线抗弯刚度(EI)new下管线受到盾构下穿影响引起的最大位移和弯矩见

(a) 位移

(b) 弯矩
图7 管线抗弯刚度变化对管-土相互作用影响
Fig.7 The influence of pipeline-soil interaction with the
variation of pipeline bending stiffness
4 结 论
本文基于理论研究的方法提出了一种盾构下穿对上覆管线变形影响的预测方法.得到的结论如下:
1) 考虑管线侧向土体对既有管线的影响,将管线简化成无限长的欧拉梁搁置在Pasternak地基上,随后采用差分形式获得管线变形简化计算结果.
2) 与该方法可退化的解析对比,本文方法计算结果更贴近既有工程实测数据,进一步证明了该方法的可靠性.
3) 增大隧道与管线的竖向净距会非线性地减小盾构下穿对上覆管线的影响;管线变形及其内力会随着地层损失率增大而线性增大;管线抗弯刚度的增大会引起管线变形减小,但会大幅增加管线弯矩.
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