明挖卸荷引起桩侧摩阻力作用下的地铁隧道竖向变形计算

为研究基坑明挖卸荷时复合地基中桩侧摩阻力对下卧地铁隧道竖向变形的影响,基于Mindlin应力解,推导得到复合地基中桩的侧摩阻力作用下地铁隧道的总竖向附加应力,利用双面弹性地基梁模型和两阶段分析方法,计算得到地铁隧道总竖向位移,并与前人理论计算结果、实测数据对比验证。最后,分析桩形状、桩截面面积、以及不同区域桩长度、间距的改变对桩侧摩阻力引起地铁隧道竖向位移的影响。结果表明:无论桩参数如何改变,复合地基中桩侧摩阻力对隧道竖向位移的影响范围始终不变,约为1. 1倍基坑纵向长度;材料用量相同的方桩与圆桩相比,方桩可更有效地控制下卧地铁隧道竖向变形;适当地增大隧道斜上方的桩长度,可使其更有效地控制地铁隧道竖向变形;隧道正上方的桩间距存在一个合理的取值范围;适当减少桩纵向间距比减少桩横向间距可更有效地控制下卧地铁隧道竖向变形。

Calculation on Vertical Deformation of Metro Tunnel under Pile Side Resistance due to Open Cutting Unloading

In order to study the effect of pile side resistance in composite foundation on the vertical deformation of underlying metro tunnel in open cutting unloading case of the foundation pit, the total vertical additional stress of metro tunnel under pile side resistance in composite foundation is derived based on Mindlin stress solution. Using foundation beam model of double elastic and two-stage method, the total vertical displacement of the metro tunnel is calculated and verified by comparison with the theoretical calculation results of the predecessors and the measured data. Finally, the effect of the change of pile shape, cross-section area, and length, spacing of piles in different areas on the vertical displacement of metro tunnel caused by pile side resistance is analyzed. The results show that no matter how the pile parameters change, the effect range of pile side resistance on tunnel vertical displacement in composite foundation remains unchanged and about 1.1 times the longitudinal length of foundation pit; square piles with the same amount of material can control the vertical deformation of the underlying metro tunnel more effectively than circular piles; properly increasing the length of the piles aslant above the tunnel can make it more effective to control the vertical deformation of the metro tunnel; there is a reasonable value range for the distance among the piles directly above the metro tunnel; the vertical deformation of the underlying tunnel can be controlled more effectively by appropriately reducing the longitudinal distance of piles than by reducing the lateral distance of ones.