下穿黄河盾构隧道管片衬砌结构受力特征模型试验

Model Test Study on the Mechanical Characteristics of Segment Linings for the Shield Tunnel Undercrossing the Yellow River

针对兰州地铁穿河段盾构隧道穿越强透水砂卵石地层和承受较高外水压的特点,首先研制了外水压加载装置,该装置在衬砌模型内部创造了一个封闭的负压环境,通过控制模型内外气压差来实现外水压的等效加载,同时结合隧道-地层复合模拟试验系统开展了几何相似比为1∶10的室内模型加载试验,实现了土压和水压的分别控制加载.研究了水压、土压、土体侧压力系数及拼装方式对管片受力特征的影响.研究结果表明,随着水压的增大,管片轴力明显提高,弯矩略有减小,偏心距则明显降低;随着隧道上覆土压的增大,管片衬砌结构的轴力、弯矩、偏心距均呈增大趋势,但总体上量值变化较小;在水压一定时,覆土厚度的增加对管片弯矩的影响越来越大,而轴力变化速率均比较稳定;正常水压条件下,随着土体侧压力系数的增大,管片衬砌结构的轴力增大,弯矩减小,偏心距减小,随着水压的增大,侧压力系数对于管片结构受力特征的影响越来越小;错缝拼装情况下,管片内力在部分环向及纵向接头处会产生较大突变,且管片内力较通缝拼装情况大.

The shield tunnel of Lanzhou metro undercrossing the Yellow River was driven under through high permeability sandy cobble stratum and under high water pressure. A device for external load- ing test was therefore developed, which introduced a controllable air pressure between the linings and grouting layer, and by regulating the pressure difference, the equivalent water pressure can be then simu-lated. Using this device together with a tunnel-ground simulation facility, a model test with a geometric similarity ratio of 1 ： 10 was conducted. The device can reach the point that the water pressure and earth pressure were controlled separately. The mechanical characteristics of segment lining with different exter- nal water pressures, soil pressure, coefficient of side earth pressure and segment assembling methods was analyzed. The results suggest that, as external water pressure increased, a significant increasing trend of axial force and a gentle decrease trend of bending moment were observed while eccentricity decreased obvi- ously; as soil pressure increased, a gentle increase of axial force, bending moment and eccentricity was ob- served; Given a fixed water pressure, increasing effects on the bending moment and decreasing effects on axial force were shown with the increase of soil pressure; Given a normal pressure level, axial force of seg- ment linings increased while bending moment decreased when the coefficient of side earth pressure in- creased, which made the eccentricity decrease. In addition, the coefficient of side earth pressure shows de- creasing effects on the mechanical characteristics of segment linings with the increasing of water pressure; Under staggered assembling, internal force of the segment will produce a mutation at some parts of cir- cumferential and longitudinal joints, besides, internal force of the segment under staggered assembling is lar^er than that under straight joint assembling.