盾构隧道施工对砂性地层的扰动及管片受荷特征

以西安地铁土压平衡式盾构穿越砂性地层为背景,采用颗粒流(PFC^2D)数值方法研究盾构施工对砂性地层的扰动情况,同时通过现场测试获取砂性地层下盾构隧道管片衬砌的荷载分布和内力特征。研究结果表明,相对于黄土等粘性地层而言,砂性地层的颗粒性较为突出,盾构开挖引起的地层移动在空间分布上连续性较差,出现局部松动或欠密实区域。砂性地层透水性较好,孔隙水压力测试值与水头高度有很好的相关性,但土压力测试值要低于实际受力值。受各种施工荷载的影响,管片弯矩和轴力在盾尾脱环阶段波动较大,随着盾构的推进,盾尾注浆等施工荷载对结构受力的影响减小,当脱出盾尾10~15环后,管片内力逐渐稳定。研究成果可为砂性地层土压平衡盾构隧道的设计与施工提供参考。

Disturbance of Shield Tunnel Construction to Sandy Stratum and Load Bearing Characteristics of Segment Lining

On the background of earth pressure balanced shield tunneling passing through sandy stratum for Xi’an Metro, the particle flow code (PFC) method was used to study the disturbance of shield tunnel construction on sandy stratum. A field test was also carried out to obtain the load distribution and internal force characteristics of shield tunnel segment lining. The results show that compared with loess stratum, the sandy stratum has more prominent features of particle. Ground displacement caused by tunnel excavation had poor continuity in spatial distribution, and partial looseness or uncompleted compacted zone occurred. There is a good permeability of sandy stratum, and pore water pressure tested in sandy stratum had good correlation with height of water head. Earth pressure tested was lower than its actual value. Influenced by shield construction loads, bending moment and axial force of segment ring had great fluctuation during the process of decyclization in the tail. With the driving of shield machine, construction loads had more slight influence on tunnel structure. When there were 10~15 rings out of shield tail, the internal force of segment ring was becoming stable. The results can offer references for the design and construction of EPB shield tunnel in sandy stratum.