上软下硬地层盾构隧道掌子面稳定支护压力分析

STABILITY ANALYSIS OF SHIELD TUNNEL HEADING FACES IN UPPER-SOFT AND LOWER-HARD STRATUM

准确控制掌子面压力是保证盾构隧道安全施工的重要因素之一,通过建立砂层占比分别为100%、87.5%、75%、62.5%、50%、37.5%、25%、12.5%的掌子面稳定性分析的三维数值模型,得到了砂层–泥质粉砂岩复合式上软下硬地层掌子面失稳破坏规律,并在此基础上推导出在上软下硬地层情况下掌子面极限支护力理论计算方法。计算结果表明:掌子面破坏模式主要受上部砂层控制,破坏面一般发生在砂土地层中;随着砂层占比的增大,掌子面极限支护力呈非线性增大趋势且当砂层占比低于75%时,掌子面极限支护力增长较快;所提出的掌子面支护力理论计算公式能较好地预测掌子面下限支护力,其结果与数值模拟计算值误差在5%以内,该计算方法可为上软下硬地层中盾构掌子面支护压力的确定提供参考。

Accurate controlling of heading face pressure is one of the important factors to ensure the safety construction of shield tunnels.Based on a series of three-dimensional numerical model for stability analysis of the tunnel face,in which the area proportions of sand layer in the tunnel excavation surface are 100%,87.5%,75%,62.5%,50%,37.5%,25%,12.5%respectively,the destabilization damage law of the tunnel face in the argillaceous siltstone composite stratum,i.e.upper-soft and lower-hard stratum,is obtained.On the basis of this,a theoretical calculation method for the ultimate support force of the tunnel heading face in the upper-soft and lower-hard stratum is deduced.The calculation results show that:the failure mode of the tunnel face is mainly controlled by the upper sand layer,with the damage surface generally occurring in sandy soil stratum;with the increasing of area proportions of sand layer,the ultimate support force of tunnel face is increased non-linearly,and when the area proportion of sand layer is smaller than 75%,the ultimate support force of tunnel face is increased faster.The proposed theoretical formula can well predict the lower limit support force of tunnel heading face,and the error between the result and the numerical simulation is within 5%,which can provide well reference for determining the support pressure of shield tunnel heading face in the upper-soft and lower-hard stratum.