迎坡条件下盾构隧道开挖面极限支护力计算与分析

Calculation and analysis of limit support force of shield tunnel excavation face under facing-slope conditions

开挖面的稳定性是盾构隧道施工技术的关键。针对目前考虑坡度因素的盾构隧道开挖面极限支护力计算尚未见到报道的现状,基于筒仓理论,采用极限平衡分析法,引入线路坡度角,建立了迎坡施工条件下,盾构隧道开挖面极限支护力的计算模型,推导了相应的计算公式,并进行了实例分析,结果表明:该方法具有很好的可靠性,可用于同类工程的设计与施工。在此基础上,进一步计算得到了不同坡度时的盾构隧道开挖面极限支护力的大小,探讨了线路坡度对开挖面极限支护力大小的影响,主要得出了以下结论:开挖面极限支护力随线路坡度增大而呈线性显著增大;而开挖面前方土体破裂角随线路坡度增大反而线性减小,且两者之和可视为一常数。可见,线路坡度的存在对开挖面支护力的影响较大,不能简单地等同为平坡条件,设计、施工过程中应予以充分考虑。

Stability of excavation face is a key problem to shield tunnel construction technology.According to the present situation that the calculation of the limit support force of shield tunnel excavation face is rarely reported,based on the silo theory,a calculation model of the limit support force due to facing-slope construction is put forward by use of the limit equilibrium analysis method,and the track gradient is introduced.The corresponding formulas are obtained by theoretical derivation,and an engineering project is analyzed as an example.The results indicate that this method is reliable and can be applied to the design and construction in similar projects.Furthermore,the limit support forces to different track gradients are calculated for discussing their influences.Conclusions are drawn as follows： the limit support force of excavation face increases largely and linearly with the increase of the track gradient;but the rupture angle of soil before the excavation face decreases linearly with it,and the sum of them is approximately a constant.It can be seen that the existence of the track gradient has significant effect on the limit support force,and it should be fully taken into account during the design and construction process.