黏土与粉土复合地层及其中地铁隧道的车致长期沉降

为了探明列车荷载对黏土与粉土复合地层及其中地铁隧道的长期影响，以无锡某地铁区段为研究对象，建立了轨道-隧道-地层系统的耦合2.5维数值模型，分析了运行列车诱发地铁隧道下覆黏土及粉土复合地层的动应力响应规律，进而结合循环荷载作用下黏土及粉土的不排水累积变形特征及孔压累积特征，采用分层总和法研究了列车振动荷载长期作用诱发该复合地层及其中地铁隧道的长期沉降量值及发展规律. 研究结果表明:1） 隧道下覆地基土的动偏应力沿深度方向呈先增大后减小的变化趋势，其最大值出现在隧道下覆约1.3 m深度处，可达2.80 kPa；2） 地铁列车运行导致复合地层中隧道结构的沉降主要发生在地铁列车前20万次运行期内，且隧道结构的沉降在此期间发展得较为迅速；3） 复合地层中隧道结构稳定后的车致沉降量值可达13.44 mm，其中由土体不排水累积塑性应变引起的沉降为11.40 mm，占比85%，由累积孔压消散引起的固结沉降为2.04 mm，占比15%；4） 隧道下覆黏土与粉土复合地层长期变形主要发生在隧道下方15 m范围内，该范围内的土体沉降对隧道结构长期沉降量值的贡献占比达90%. 

Long-Term Settlements of Composite Stratum of Clay and Silt and Metro Tunnel in It Due to Train Operation

In order to find out the long-term effects of train load on the composite stratum of clay and silt and the metro tunnel in it, the dynamic response characteristics of this kind of composite stratum under a metro tunnel in a typical section of Wuxi Metro lines due to the moving train were firstly studied through a 2.5-dimensional (2.5D) track-tunnel-ground coupling model. Based on this, combined with the undrained deformation accumulated characteristics and the pore water pressure accumulated characteristics of corresponding soils under the cyclic loading, the developments of the long-term settlements of the concerned composite stratum and the tunnel structure due to the train vibration loads were finally obtained and analyzed through the layered summation method. The analysis results show that: 1) the dynamic deviatoric stress of the foundation soil under the tunnel increases first and then decreases with the increase of the depth, and its maximum value can reach 2.8 kPa, which appears at the position with a distance of 1.3 m to the tunnel invert; 2) the train-induced settlement of tunnel structure in the composite stratum mainly occurs within the first 200000 operation periods of metro trains, and it develops rapidly during these periods; 3) the stable train-induced settlement of tunnel structure in the composite stratum has a magnitude of 13.44 mm, in which the part caused by the accumulated undrained plastic strain of soil is 11.40 mm, accounting for 85% of the total value, while the part caused by the dissipation of accumulated pore water pressure and the corresponding consolidation of soil is 2.04 mm, accounting for 15% of the total value; 4) the long-term deformation of the composite stratum of clay and silt mainly occurs within 15 m below the tunnel, and the contribution of soil settlement within this range to the magnitude of the long-term settlement of the tunnel structure can account for 90%.