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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 the tunnel caused by the construction disturbance in the peat soil layer, the soil surrounding the tunnel is regarded as a continuous, homogeneous and isotropic saturated viscoelastic medium. The five-element model is used to describe the rheological properties of the peat soil , Coupled with the Terzaghi-Rendulic two-dimensional consolidation theory, a governing equation for the dissipation of excess pore water pressure in the surrounding soil caused by shield construction disturbances under completely impervious conditions was established. The governing equations are solved by using the methods of separation of variables, conformal mapping, Laplace transformation and inverse transformation. The analytical solutions of the dissipation of excess pore water pressure around the tunnel are obtained. Finally, the vertical strain of the soil is obtained by integration The long-term settlement of the tunnel formula. A case study was conducted to analyze the variation of excess pore water pressure dissipation and tunnel long-term settlement in Kunming peat soil layer. The results show that compared with Shanghai soft clay, the dissipation velocity of excess pore water pressure in peat soil layer in initial stage Faster, then quickly slows and tends to stabilize. In the peat soil layer, the long-term settlement of the tunnel lasted longer and the settlement was larger. The settlement of the tunnel tended to be stable within 900 days, with a cumulative settlement of about 150 mm. In addition, the rheological properties of Kunming peat soil is significant. If the excess pore water pressure in the soil is dissipated by 90% as the completion time of the main consolidation settlement, the soil sub-consolidation settlement accounts for about 36% of the total settlement of the tunnel. Tunnel long-term settlement can not be ignored in an important part.