Railways are one of the largest transportation networks in the world. One of the key subgrade problems of railway track is associated with progressive shear failure (PSF). To-date, limited number of studies have addressed failure mechanism associated with the PSF, especially extending the mechanics of unsaturated soils. In this paper, the PSF mechanism is studied with the aid of computer program that was developed using a Visual Basic program in AutoCAD, extending Mohr-Coulomb failure criteria within the unsaturated soil mechanics framework. Simulation results suggest several parameters that include stress distribution, matric suction, cohesion, coefficient of lateral earth pressure at rest, and coefficient of residual friction as well as the angle of internal friction have a significant effect on the PSF and the shape of failure planes in the subgrade. The PSF in subgrade can be reduced by optimizing the combination of these parameters. The simulation results suggest the PSF can be well simulated with the Mohr-Coulomb failure criteria.

铁路是世界上最大的交通网络之一。铁路轨道的关键路基问题之一与渐进式剪切破坏（PSF）有关。迄今为止，数量有限的研究已经解决了与PSF相关的破坏机理，特别是扩展了非饱和土的力学。在本文中，借助于在AutoCAD中使用Visual Basic程序开发的计算机程序来研究PSF机制，从而在非饱和土力学框架内扩展了Mohr-Coulomb破坏准则。仿真结果表明了几个参数，包括应力分布，矩阵吸力，内聚力，静止时的侧向土压力系数，残余摩擦系数和内摩擦角对路基的PSF和破坏面的形状有重要影响。可以通过优化这些参数的组合来降低路基中的PSF。仿真结果表明，使用Mohr-Coulomb失效准则可以很好地模拟PSF。