考虑地层损失的隔离桩对基坑旁侧盾构隧道变形保护研究

Deformation protection of shield tunnels next to foundation pits by isolation piles considering formation loss

基坑的开挖卸载会导致旁侧既有盾构隧道出现变形破坏,工程中常在基坑与隧道之间设置隔离桩来保护既有隧道。为研究基坑开挖影响下隔离桩外既有隧道的水平位移规律,建立基坑、隔离桩、既有隧道的三维力学计算模型,考虑基坑开挖引起的地层损失,推导了基坑卸荷引起的附加应力计算公式,基于Kerr地基模型并对地基系数做出调整,得到隔离桩挠曲变形计算公式,建立隔离桩挠曲变形影响区,根据影响区的地层损失推导了既有隧道水平位移计算公式,同时进行了案例验证与影响因素分析,对隔离桩的“牵引作用”与“保护作用”在理论上做出了解释。研究结果表明:计算结果与工程实测数据及数值模拟结果相互吻合;设置隔离桩能够有效降低隧道水平位移,起到很好的保护作用;保护作用随着隔离桩桩长的增加而逐渐增加;桩长达到临界点后,隔离桩“牵引作用”产生,保护作用随桩长增加而减小;桩间距较小时保护效果较好;隔离桩设置靠近基坑一侧时保护效果明显优于设置在靠近隧道一侧。

The excavation and unloading of a foundation pit will lead to the deformation and destruction of the adjacent tunnels.In engineering,the isolation piles are often set between the foundation pit and the tunnel to protect the tunnel.In order to study the horizontal displacement laws of the existing tunnels outside the isolation piles under the influences of excavation of foundation pits,a three-dimensional mechanical model is established.Considering the stratum loss caused by excavation of foundation pits,the formula for the additional stress caused by unloading of the foundation pits is derived.Based on the Kerr foundation model and the adjustment of the foundation coefficient,the formula for the deflection deformation of the isolation piles is obtained.Based on the formation loss in the affected area,the formula for calculating the horizontal displacement of the existing tunnels is deduced.At the same time,the case is verified and the influencing factors are analyzed.The"traction effects"and"protection effects"of the isolation piles are explained theoretically.The results show that the calculated results are consistent with the measured data and numerical results.Setting isolation piles can effectively reduce the horizontal displacement of the tunnels and play a good protective role.The protective effects of the short piles gradually increase with the increase of the length of the isolated piles.After the pile length reaches the critical point,the"traction effects"of the isolation piles occur,and the protective effects decrease with the increase of the pile length.The protection effects are better when the pile spacing is small.When the isolation piles are placed close to the side of the foundation pit,the protection effects are significantly better than those of the side close to the tunnels.