基于变形时间效应的高速铁路地基压缩层厚度计算方法

路堤荷载作用下地基变形是高速铁路路基沉降的主要来源,地基有时间效应的变形是引起高速铁路长期服役性能劣化的核心因素,掌握具有变形时间效应的地基土层区域是合理计算地基工后沉降、优化地基加固方案的技术关键.基于分形的无标度特性,确立塑性变形速率随时间的分形关系,揭示了地基土变形随荷载水平呈现快速稳定、长期稳定、长期破坏和快速破坏的四种演化状态类别,提出了表征变形速率变化快慢的土体变形状态"分维数判别法";开展了单元结构填土模型和三轴流变试验,获得了中低压缩性粉质黏土的变形状态荷载阈值及其与抗剪强度或极限承载力的比值;基于摩尔-库伦准则,采用强度折减方法,获得了地基土变形状态强度参数,结合地基土中应力,得到了由库伦强度理论表达的变形状态控制方程,明确了地基沿深度具有时间效应变形区域的深度即为基于变形时间效应的地基压缩层厚度.提出的"时间效应法"确定压缩层厚度为进一步完善高速铁路的地基沉降计算提供了理论依据和实验支撑.

Calculating method based on deformation time effect on thickness of compressible stratum in high-speed railway foundation

Deformation of foundation on embankment load is the main reason of subgrade settlement in high-speed railway, time-effect deformation of foundation is the core element that degrades the long-term service performance of high-speed railway, and deter- mining the foundation area with time-effect deformation is the key point of calculating foundation settlement in order to control the post-construction settlement. Based on the scale-free characteristic of fractal theory, fractal relationship between plastic deformation rate and the time is established, revealing that soil under different load levels presents four kinds deformation evolution states of fast stability, long-term stability, long-term damage and rapidly damage. To discriminate deformation states, the ＂fractal demention criterion＂ representing plastic deformation rate variety is put forward. At the same time, the rheological tests on the triaxial and unitstructure filling model are carried out to obtain the deformation state thresholds of the soft clay with low and medium compressibility, further more the ratios between the thresholds and ultimate shear strength or ultimate bearing capacity experimentally. In view of Mohr-Coulomb criterion, using the equal proportion strength reduction method, state strength parameters on the deformation of foundation soil are received. On account of the stress state of foundation soil, the deformation state controlling equation on Coulomb strength theory is gained, and clear time-effect deformation area of foundation along depth, the thickness of which is thickness of compressible stratum on the foundation time-effect deformation. This calculation method based on deformation time effects on thickness of foundation compressible stratum provides a theoretical basis and experimental support for further improvement of high-speed railway foundation settlement calculation theory.