青岛地铁大断面隧道围岩变形特性及施工方案优化

Deformation Characteristics of Large Section Tunnel Surrounding Rock and Optimization of Tunnel Construction Scheme for Qingdao Metro Line

[目的]大断面隧道由于其形状扁平且跨度较大,一般采用多台阶多分步开挖,在施工过程中反复扰动围岩和临时支撑,影响围岩及支护结构稳定性,故须对其围岩变形特性进行研究,并优化施工方案。[方法]以青岛地铁4号线折返区间暗挖隧道为例,结合现场监测数据,通过有限元模拟分析现行施工方案中大断面地铁隧道三台阶九步开挖过程中的围岩变形特性,并与优化后的三台阶五步法做模拟对比。[结果及结论]模拟比较结果表明,现行施工方案横向距离隧道中心线26 m范围内的地面沉降较大,占总沉降量的89.77%;拱顶和拱肩在开挖后变形大,沉降量最大达到10.2 mm,拱顶围岩应力随开挖迅速增加,随着开挖工序推进,拱腰上部和墙角出现局部主应力集中。优化后的三台阶五步开挖法可实现快速开挖和支护,施工工序简化40%,同时减少了围岩扰动,其变形可控制在10 mm的合理范围内,改善了拱顶的应力重分布和墙角的应力集中现象。

[Objective]The large section tunnel,due to flat shape and large span,usually adopts multiple steps and staged excavation.In the process of construction,the surrounding rock and the temporary support are repeatedly disturbed,affecting the stability of surrounding rock and supporting structure.Therefore,the deformation characteristics of the surrounding rock should be studied and the construction scheme should be optimized.[Method]Taking the mined tunnel of Qingdao Metro Line 4 in turn-back section as the example,based on the on-site monitoring data and using finite element simulation,the deformation characteristics of the surrounding rock in the excavation process of the large-section metro tunnel with three-step and nine-stage method are analyzed,and then compared with the optimized three-step and five-stage method.[Result&Conclusion]The simulation results show that the ground settlement is relatively large caused by the current construction scheme within the horizontal distance of 26 m from the tunnel center line,accounting for 89.77%of the total settlement.The arch and the spandrel deform are large after excavation,and the maximum settlement reaches 10.2 mm.The stress of the surrounding rock of the arch increases rapidly with excavation.As the excavation advances,the local principal stress concentration appears in the upper part of the haunch and the corner.The optimized three-step and five-stage excavation method can realize rapid excavation and support,and simplify the construction process by 40%,while reducing disturbance to the surrounding rock and controlling its deformation within a reasonable range of 10 mm.Thus,the stress redistribution of the arch and the stress concentration in the corner are improved.