考虑坡度角的砂卵石地层盾构隧道开挖面稳定性研究

Study on Excavation Face Stability of Shield Tunnel in Sandy Cobble Stratum Considering Slope Angle

随着盾构隧道在城市中的应用越来越广泛,盾构隧道穿越的地层及障碍物的类型也愈发多样。为满足盾构隧道运营及穿越复杂地层或绕避重要构筑物的要求,盾构隧道线型设计中多采用一定的线型坡度角。现阶段关于坡度角对于盾构隧道开挖面稳定性影响的研究尚不全面,为研究不同坡度角对砂卵石盾构隧道开挖面稳定性的影响,以某砂卵石地层土压盾构项目为依托,基于极限平衡理论模型,采用离散元数值模拟对考虑隧道线路坡度角情况下的砂卵石地层盾构隧道开挖面失稳机理进行了分析。结合线路坡度角对极限分析上限解模型进行改进,并选用现有考虑线路坡度角的极限平衡法、极限分析法理论解与数值模拟结果进行验证。研究结果表明:开挖面极限支护压力受土体摩擦力、隧道直径与土体黏聚力影响,随着隧道直径由3 m增加到15 m,掌子面支护压力逐渐增加,而随着黏聚力逐渐增大,支护压力逐渐减小至0;同样条件下掌子面俯仰角10°时的支护压力大于俯仰角水平、-5°及-10°工况;当考虑坡度角计算开挖面极限支护压力时,仰角工况相对于水平工况及俯角工况更不利于开挖面的稳定。因此,在设计阶段,设计人员需要特别关注盾构穿越地层的地质情况综合确定线型,保障后续施工安全,当盾构遇到砂卵石地层上坡时,施工人员需要严格控制土舱压力及单环出土量。

With the increasing application of shield tunnels in cities,the types of strata and obstacles that shield tunnels cross are becoming more and more diverse.In order to meet the requirements of shield tunnel operation and crossing complex strata or avoiding important structures,a certain linear slope angle is often used in the linear design of shield tunnels.At present,the research theory on the influence of slope angle on the stability of excavation face of shield tunnel is not comprehensive.In order to study the influence of different slope angles on the stability of excavation face of sandy pebble shield tunnel,this paper is based on a sandy pebble stratum earth pressure shield project.Based on the limit equilibrium theory model,the discrete element numerical simulation is used to analyze the instability mechanism of excavation face of shield tunnel in sandy pebble stratum considering the slope angle of tunnel line.The upper bound solution model of limit analysis is improved by combining the line slope angle,and the existing limit equilibrium method,limit analysis method theoretical solution and numerical simulation results considering the line slope angle are selected for verification.The results show that the ultimate the increase of tunnel diameter from 3 m to 15 m,the support pressure of tunnel face increases gradually,with the increase of cohesion,the support pressure decreases gradually to 0.Under the same conditions,the support pressure at the pitch angle of 10°is greater than that at the pitch angle of horizontal,-5°and-10°.When considering the slope angle to calculate the limit support pressure of the excavation face,the elevation condition is more unfavorable to the stability of the excavation face than the horizontal condition and the pitch condition.Therefore,in the design stage,designers need to pay special attention to the geological conditions of the stratum through which the shield passes to comprehensively determine the line type to ensure the safety of subsequent construction;when the shield encounters the sand pebble stratum uphill,the construction personnel need to strictly control the soil chamber pressure and the single ring unearthed amount.