滇池泥炭土层地铁盾构施工扰动引起长期沉降的机理研究

Soil disturbance is unavoidable during shield tunnelling, especially in Dianchi peat soil with high organic content, high sensitivity and notable creep property, which will induce long duration deformation and too large settlement after construction. For studying the long-term settlement of soil induced by shield tunnelling in peat soil, construction parameters and field test are combined to reveal the soil disturbance mechanism, put forward the quantitative index for evaluating soil disturbance and mathematical model of excess pore water pressure dissipating. Based on uniaxial compression test, microscopic scanning, triaxial creep test, permeability test, et al, the creep and seepage characteristics of Dianchi peat soil are investigated from both microscopic and macroscopic point of view, and the corresponding creep-consolidation coupling model is proposed. Combined with the time-dependent properties of Dianchi peat soil, the mathematical model for predicting long-term settlement caused by shield tunneling in peat soil is established, considering the influence of boundary condition and initial condition. And its validity will be proved by practical engineering. The goal of this project is to provide reliable theoretical basis for reducing the effect on surrounding environment due to shield tunnelling in peat soil. It has not only important academic value, but also considerable significance of application.

盾构在掘进过程中不可避免地会对周围土体产生扰动，而滇池泥炭土有机质含量高、灵敏度高、蠕变特性显著，施工扰动之后土体变形的持续时间较长，在工程建设中容易产生工后沉降过大的问题。为研究地铁盾构在泥炭土层中掘进时因施工扰动引起周围土体的长期沉降问题，拟将盾构施工参数及现场试验实测数据相结合，揭示盾构在泥炭土层掘进对周围土层的扰动机理，建立评价土体扰动的量化指标及超孔隙水压力消散的数学模型；通过单向压缩试验、微观观测试验、三轴蠕变试验、有压渗透试验等综合试验方法，从微观及宏观的角度研究滇池泥炭土的蠕变及渗透特性，提出相应的蠕变-固结耦合模型；结合滇池泥炭土的变形时效特性，考虑边界条件、初始条件的影响，建立预测盾构在泥炭土层中掘进引起周围土体长期沉降的数学模型并结合实际工程验证其有效性。本研究为减小盾构在泥炭土层施工对周边环境的影响提供理论依据，不仅具有学术研究价值，还有重要的工程应用前景。

为研究盾构在滇池泥炭土层中掘进时因施工扰动引起周围土体的长期沉降问题，将试验研究与理论分析相结合，开展了盾构掘进对周围土体的扰动机制、滇池泥炭土的物理力学特性及孔隙结构特征的统计规律、原状及扰动滇池泥炭土的固结蠕变及直剪蠕变特性以及盾构施工扰动所引起的长期沉降问题等方面的研究工作。首先，基于修正剑桥模型，采用应力路径法计算得到了盾构施工引起周围土体的超孔隙水压力峰值；考虑开挖面土仓压力、隧道中心处的静止土压力及土体粘聚力等因素的影响，确定了盾构施工引起周围土体超孔隙水压力的影响范围；根据达西定律推导出隧道周围土体超孔隙水压力分布的数学模型。以大量的滇池泥炭土物理力学指标试验数据为基础，采用统计分析方法研究其物理力学指标的统计分布规律及指标间的相关性。基于CT扫描试验，采用数字图像处理技术建立了表征泥炭土孔隙结构特征的三维空间结构模型，分析了不同方向截面孔隙率的变化特征，并考虑孔隙连通性的影响讨论了土体切片图像中孔隙团的分布规律。针对不同埋深滇池泥炭土进行固结蠕变试验，得到了各级固结压力作用下原状与扰动土样压缩量和固结时间的对应关系，以及压缩指数与次固结系数的变化规律。基于直剪蠕变试验，得到了不同固结压力及剪应力作用下，描述滇池泥炭土流变特性的五元件粘弹性模型。根据滇池泥炭土的粘弹性模型，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及预测隧道长期沉降的数学模型，并结合工程实例验证其有效性。研究成果能够揭示盾构在掘进过程中对周围土体的扰动机理及滇池泥炭土的固结蠕变时效特性，并从理论上对滇池泥炭土层盾构施工扰动引起的长期沉降问题加以解释，具有较好的学术价值和重要的工程应用前景。