考虑荷载波形效应的高速铁路地基软黏土长期累积变形机理研究

In the deep soft soil area, large post-construction settlement of high speed railway foundation can be produced under vibration loads. The theory and model for its settlement prediction are mostly based on the experimental results by use of simple cyclic loads (e.g., sine, rectangular, and triangular cycle load), however, these kinds of loads are difficult, or even impossible to fully capture the complex features of high speed train (HST) loads such as long-term application, low stress level, principal stress rotation. To solve this problem, we intend to investigate the features of HST loads by dynamic response of track and foundation, and then synthesize a vibration load capturing these features and apply it into the indoor experiments. To this end, a complete nonlinear coupling vibration model involving vehicle-track-subgrade-foundation is established based on the Hertz nonlinear wheel-rail contact theory, which is a classical method to model the interaction between vehicle and track. After complete the numerical solution and verification of the proposed model, characteristics of dynamic response of soft foundation are theoretically studied. Then, with dynamic response analysis, features of HST load directly applied on the foundation soils are studied, and several of key waveform parameters of the loads are determined combining with field vibration test results. And a new vibration load is synthesized by these parameters. Dynamic triaxial tests and hollow cylindrical tests for undisturbed soft clay are conducted under the synthesized vibration loads, and dynamic characteristics of soft clay are comprehensively explored based on test results. Then, with considering waveform effect of load, a new dynamic constitutive model is put forward by use of the elastic-plastic incremental theory in non-isotropic hardening modulus field. After embedding the model into the existing finite element method, the influence of load waveform parameters, stress level and drainage condition on the cumulative deformation are analyzed, and a new computation method for long-term cumulative deformation of soft soil in high speed railway foundation, which will be verified and validated by monitoring test results. The results of this project can provide a reasonable scientific base for the prediction and control of long-term deformation and settlement of soft foundation of high speed railway.

深厚软土地区高速铁路振动荷载作用下地基产生较大的工后沉降，而目前对其计算预测的理论和模型大都是基于简单循环荷载的试验结果而建立，不能完全反映高速铁路振动荷载的复杂特性如长期性、低幅值和主应力旋转等。本项目引入车辆轨道动力学中的Hertz非线性轮轨接触理论，考虑轨道随机不平顺，建立车辆-轨道-路基-地基耦合振动模型，并完成数值求解和验证，分析软土地基动力响应特性，进而确定直接作用于地基土体上的振动荷载的波形特征参数，并合成室内试验所需的振动荷载波形，通过动三轴和空心圆柱试验，研究软黏土的动力变形特性，进而考虑荷载波形效应，依据非等向硬化模量场增量弹塑性理论建立动力本构方程，与有限元结合分析荷载参数、应力水平、排水条件等对累积变形的影响规律，提出高速铁路长期振动荷载作用下地基软黏土累积变形计算方法，并结合实际工程验证。研究成果可为高速铁路软土地基长期变形沉降的预测和控制提供合理科学依据。

深厚软土地区高速铁路振动荷载作用下地基产生较大的工后沉降，而目前对其计算预测的理论和模型大都是基于简单循环荷载的试验结果而建立，不能完全反映高速铁路振动荷载的复杂特性如长期性、低幅值和主应力旋转等。本项目引入车辆轨道动力学中的Hertz非线性轮轨接触理论，考虑轨道随机不平顺，建立车辆-轨道-路基-地基耦合振动模型，并完成数值求解和验证，分析软土地基动力响应特性，进而确定直接作用于地基土体上的振动荷载的波形特征参数，并合成室内试验所需的振动荷载波形，通过动三轴和空心圆柱试验，研究软黏土的动力变形特性，进而考虑荷载波形效应，依据非等向硬化模量场增量弹塑性理论建立动力本构方程，与有限元结合分析荷载参数、应力水平、排水条件等对累积变形的影响规律，提出高速铁路长期振动荷载作用下地基软黏土累积变形计算方法，并结合实际工程验证。研究成果可为高速铁路软土地基长期变形沉降的预测和控制提供合理科学依据。