大断面深埋高水压地铁盾构隧道周边土压力作用模式评价

Evaluation of earth pressure around a deeply buried metro shield tunnel with a large cross-section under high water pressure conditions

以南京某大直径地铁盾构隧道为背景,对盾构管片衬砌所受荷载及结构内力进行现场测试,分析了深埋高水压粉细砂地层中盾构隧道管片土压力大小及分布特征。采用3种不同竖向荷载组合(即有效上覆土压力+水压力,太沙基松动土压力+水压力,只有水压力)计算管片内力并与实测内力进行比较,评价了作用在盾构隧道管片上的土压力模式。结果表明:(1)作用在盾构隧道衬砌上的水压力大小基本等于静止水压力;(2)盾构隧道隧顶实测土压力约为太沙基松动土压力的80%,实测隧顶土压力更接近于太沙基松动土压力,隧道上方存在土拱;(3)现场实测管片弯矩较3种荷载作用下计算弯矩小,而实测管片轴力约为理论计算轴力的2倍。此外,分析了水平地基抗力系数对隧道管片内力的影响。研究成果可为大直径深埋盾构隧道设计提供参考。

A field monitoring program is performed to measure the earth pressures acting on the linings and the intemal forces in segments of a slurry shield tunnel of Yangtze River tunnel project in Nanjing. The magnitude and distribution oft_he earth pressure are analyzed around the tunnel deeply buried in a silty sand stratum with high pore water pressure. The internal forces in the segments of concern are calculated under three different vertical loading combinations（i.e, effective overlying soil pressure plus water pressure, Terzaghi＇s soil pressure plus water pressure, and water pressure only ）, and the results are compared to the ones measured in the field. The results show that： 1） the water pressure acting on the shield tunnel lining is almost equal to the theoretical hydrostatic pressure; 2） the observed vertical earth pressure on the crown of shield tunnel accounts for about 80% of that yield by the Terzaghi＇s soil pressure plus water pressure formulation, showing soil arching effect exists above the tunnel; 3） the observed bending moments are smaller than theoretical results of the three combination methods, and the measured axial forces are approximately twice as much as the theoretical results. In addition, the influence of the ground reaction on the internal force in the segments is also discussed. The insights provided from this study can contribute to the improvement of large-section shield lining design.