饱和层状参数变异地基地下铁道车致动力响应可靠度模型

Sedimentary facies have layered and water-saturated characteristics. Due to the sedimentary history, the spatial variability of the soil parameters is considerable. Rail transit tunnels constructed in such ground often have large differential settlements and abnormal vibrations under the moving train loads. Existing vehicle-track-tunnel-soil models for calculating train-induced dynamic response fail to consider both the layered and spatial variability characteristics of saturated soils. However, a large number of rail transit tunnels are located in the saturated soils with these two characteristics. It is urgent to develop a dynamic model to describe the layered and spatial variability characteristics of the soils in the underground railway system. In this study, a reliability model for calculating the train-induced dynamic response of the underground railway in multi-layered saturated soils with spatial variability will be proposed. The dynamic system matrix for a multi-layered poroelastic half-space will be obtained by using transfer matrix method. The tunnel will be coupled with the multi-layered half-space soil by using the transformation between the cylindrical waves and the plane waves. The vehicle, rail, track slab and tunnel will be coupled by the compatibility of force and displacement conditions at the contact surface. As result a vehicle-track-tunnel-saturated soil model for calculating the train-induced dynamic response can be obtained. The accuracy of the proposed model will be verified by the field data. Considering the spatial variability of the soils, the random field of the soil parameters can be simulated by the Cholesky decomposition. After that the proposed reliability model can be established and the effect of the layered and spatial variability characteristics of the soils on the dynamic response of the system can be investigated. The research results obtained in this project will provide theoretical basis for the line selection and the determination of design parameters in underground railway engineering.

滨相沉积地基常呈层状且富水饱和，由于受沉积历史的影响，土体参数的空间变异性大。修建于此类地基中的轨道交通隧道，在行车荷载作用下常发生超常的差异沉降和振动异常。现有的车辆-轨道-隧道-饱和地基动力学模型无法考虑土体的分层及参数空间变异性，而大量轨道交通隧道处于兼具上述二重特性的饱和地基中，为此，亟需发展相应的饱和分层地基地下铁道车致动力响应可靠度模型。本项目拟首先采用传递矩阵法与面波转换法，获得隧道-饱和分层土体系统动力响应封闭解；进一步耦合轨道和车辆荷载，建立车辆-轨道-隧道-饱和分层土体系统动力响应确定性计算模型，并采用现场实测数据进行验证；在此基础上，考虑土体参数的空间变异性，基于Cholesky分解构建参数随机场，最终建立饱和分层地基地下铁道车致动力响应可靠度模型，研究土体分层及参数空间变异性对系统动力响应的影响。项目研究成果可为地下铁道的技术选线和其它设计参数的确定提供理论基础。

目前，地铁隧道车致振动预测模型中，对于弹性波传播主要媒介-土体的模拟仍存在诸多简化，如未考虑真实地基土的多类型介质（干土、饱和土、非饱和土）共存、参数空间变异性、土体及结构沿线路纵向变化等复杂特性。为此，本项目从解析和数值方法的角度，考虑地基土的上述复杂特性对系统动力响应的影响，开展了多相层状地基地铁隧道车致动力响应计算模型的研究，包括：.（1）基于非饱和土实用波动方程，推导了半空间地基-隧道系统动力响应基本解。采用非饱和参数退化的方式，建立了多相介质共存地基地铁隧道车致动力响应解析模型。.（2）建立了非饱和介质动力响应分析的有限元-完美匹配层模型。结合自由波传播理论，提出了非饱和土-结构动力响应的多耦合周期性有限元方法。.（3）提出了多相层状地基-隧道动力响应的欧拉梁计算模型，采用Cholesky分解的中点法生成参数随机场，考虑地基土体变异性对系统动力响应的影响。.重要结论包括：.（1）土体饱和度的改变会引起地基土体动剪切模量、有效应力系数、弹性波的波长等发生改变，因此土体饱和度对系统动力响应分布规律与幅值有明显影响，其中超孔隙水压力受饱和度的影响尤为显著。此外土体的临界速度随着土体饱和度的减小而增大。.（2）地基土体大尺度空间变异性即多类型介质共存特性以及纵向变化特性，会使得地基土体中产生新的散（折）射面，其会改变弹性波的传播特性，如反射和折射，以及地基的渗流条件。因此，地基土体的大尺度空间变异性对地基-隧道系统的动力响应有较大影响。.（4）地基土体的小尺度空间参数随机场变异性对系统动力响应分布影响较小，其主要影响动力响应幅值。随机场构造参数对系统动力响应均值影响较小，其主要影响动力响应预测结果的变异系数。