基于现场实测数据,详尽分析了某粉砂性地层中近距离双线顶管从上方穿越既有运营地铁隧道过程中的环境影响,包括横向地表沉降分布、沉降随时间发展、地铁隧道上浮等规律.研究发现:单线顶管横向地表沉降曲线呈现为“V”形,双线顶管横向地表沉降曲线为不对称“W”形,且后行顶管轴线上方的地面沉降大于先行顶管;后行顶管施工期间,先行顶管轴线上方地面也产生明显沉降.Peck公式在顶管施工引起的地表沉降曲线预测中适用性较好:案例中对于单线顶管,沉降槽宽度参数为0.79,土体损失率为1.6%;对于双线顶管,先行、后行顶管的沉降槽宽度参数分别为0.74和0.58,前者是后者的1.28倍;先行、后行顶管土体损失率分别为2.41%和3.11%,后者是前者的1.29倍.顶管顶进使下卧地铁隧道的纵向产生“W”形竖向位移分布曲线,顶管穿越完成后隧道的上浮存在滞后性;平行顶管上跨施工对下方地铁盾构隧道的纵向影响范围约为4~6倍顶管管径.后行顶管穿越监测断面时产生的瞬时沉降大于先行顶管;采用全方位高压喷射(MJS)工法预加固隧道上方粉砂土时降低了原状土的渗透性,顶管穿越后地面沉降仍将持续一段时间,可采用指数函数描述瞬时沉降发生后沉降随时间的发展规律.

Based on the field measured data of a double-line parallel power pipe jacking upper span subway shield tunnel, the environmental impact of a short-distance double-line pipe jacking in sandy silt stratum in the process of crossing over the existing subway tunnel was analyzed in detail, including the transverse surface settlement distribution, the development of settlement with time, and the floating of subway tunnels. The results show that the horizontal surface settlement curve of single pipe jacking presents a “V” shape, while the horizontal surface settlement curve of double line pipe jacking is an asymmetric “W” shape. The settlement of ground surface above the axis of the later pipe jacking is larger than that of the first pipe jacking. During the construction of the later pipe jacking, the settlement above the axis of the first pipe jacking is also obvious. The Peck formula has a good applicability in predicting surface settlement curve caused by pipe-jacking construction. For single-line pipe-jacking, the width parameter of settlement trough is 0.79, and the ground loss ratio is 1.6%. For double-line pipe jacking, the width parameter of settlement trough of the first and later pipe jacking are 0.74 and 0.58 respectively, and the former is 1.28 times of the latter. The soil loss ratio of the first and the second pipe jacking are 2.41% and 3.11% respectively, and the latter is 1.29 times of the former. Pipe jacking causes the vertical displacement distribution curve of the “W” shape in the longitudinal direction of the underlying subway tunnel. There is a lag in the up-floating of the tunnel after the completion of pipe jacking crossing. The longitudinal influence range of the parallel pipe jacking construction on the subway shield tunnel is about 4~6 times the pipe jacking diameter. The instantaneous settlement generated by the later pipe jacking across the monitoring section is greater than that generated by the first pipe jacking. The permeability of the undisturbed soil is reduced when the silty soil above the tunnel is pre-reinforced by the metro jet system (MJS). The ground settlement will continue for a period of time after the pipe jacking crossing. The exponential function can be used to describe the development of the settlement with time after the instantaneous settlement occurs.