泥炭质土层盾构施工扰动引起隧道长期沉降的研究

Long-term settlement of tunnel caused by shield tunneling in peaty soil

为了研究泥炭质土层盾构施工扰动引起隧道的长期沉降问题,将隧道周围土体视为连续、均质、各向同性的饱和黏弹性介质,采用五元件模型描述泥炭质土的流变特性,耦合Terzaghi-Rendulic二维固结理论,建立了隧道衬砌在完全不透水的情况下,盾构施工扰动引起周围土体超孔隙水压力消散的控制方程。采用分离变量法、保角映射、Laplace变换及逆变换等数学方法对该控制方程进行求解,得到了隧道周围土体超孔隙水压力消散的解析解,最后对土体的竖向应变进行积分获得了隧道长期沉降的计算公式。结合一工程算例分析了昆明泥炭质土层超孔隙水压力消散及隧道长期沉降的变化规律,研究结果表明:与上海软黏土相比,在初始阶段泥炭质土层中超孔隙水压力的消散速度较快,然后迅速变缓并趋于稳定。泥炭质土层中隧道的长期沉降持续时间更长且沉降量更大,在900 d的时间内隧道沉降趋于稳定,其累积沉降量约高达150 mm。此外,昆明泥炭质土的流变特性显著,如将土体中超孔隙水压力消散90%作为主固结沉降的完成时刻,则土体次固结沉降约占隧道总沉降量的36%,是隧道长期沉降中不可忽视的一个重要组成部分。

In order to study the long-term settlement of tunnel caused by shield tunneling in peaty soil, the surrounding soil of tunnel is regarded as continuum, homogeneous and isotropic saturated viscoelastic medium. The theological properties of peaty soil are described a five-component model. Based on the Terzaghi-Rendulic theory of two-dimensional consolidation, the governing equation for dissipation of the excess pore water pressure are established when the lining is impermeable. The equations are solved using the mathematical methods of separating variables, conformal mapping, Laplace transform and inverse transform, and the analytical solution of the dissipation of excess pore water pressure is obtained. Finally, the vertical strain of soil is integrated to get the formula for long-term settlement of tunnel. The variation laws of the disspation of excess pore water pressure and long-term settlement of tunnel in peaty soil are analyzed through an example. The results show that in the initial stage, the dissipating speed of the excess pore water pressure is faster than that in soft clay in Shanghai, and then it becomes slow and steady. The lasting time of long-term settlement is longer and the settlement amount is larger in the peaty soil. The tunnel settlement tends to be stable in 900 days, and the cumulative settlement is almost up to 150 mm. In addition, the rheological properties of peaty soil in Kunming are significant; if the excess pore water pressure is dissipated by 90% as the completion time of the primary consolidation settlement, the secondary consolidation settlement accounting for about 36% of the total settlement of tunnel is an important part of the long-term settlement of tunnel.