碎石集料变形机理的块体元数值试验分析

块碎石作为道砟材料能够分散列车动荷载， 加之其内部含有大量空隙， 具有良好的对流换热特性， 作为冷却冻土路基的材料在青藏铁路建设中被广泛使用。但在列车荷载的作用下， 碎石集料会发生压密、 变形乃至破碎从而影响冷却效果。因此， 研究碎石层的变形过程及机理具有十分重要的现实意义。基于块体离散元法， 对块碎石集料的三轴剪切试验进行了数值分析， 将所得应力-应变曲线与室内试验结果进行了对比， 发现两者能较好地吻合， 说明块体离散元法能够较好地模拟块碎石集料的受力变形过程。结果表明： 增大围压或块体粒径， 块体单元受到的作用力加强， 集料的偏应力强度和抗剪强度值也随之增大。碎石块体在剪切作用下沿其接触面滑动分离， 形成X形剪切带是集料变形的主要形式， 此外在径向方向出现不同程度的扩张。基于试验和块体元研究路基碎石层的思路和方法可为今后评估青藏铁路碎石路基的热力稳定性提供理论依据和参数储备。

Deformation process and mechanisms of crushed rock aggregate analyzed by numerical experiment of discrete element method

As a ballast material， the crushed rock is able to disperse train dynamic load， and it has a distinct characteristic of good convective heat transfer characteristics. Therefore， it was extensively used to cool the permafrost embankment in Qinghai-Tibet Railway. However， the crushed rock layer is compacted and even crushed under train load， so the cooling effect of the crushed rock layer decreases. For this reason， it is very important to study deformation process and mechanisms of the crushed rock layer. In this study， numerical simulations on triaxial tests of the crushed rock were carried out by the discrete element method （DEM）. A comparison between experimental and numerical results show they well agree with each other， which implies the DEM can simulate the deformation process of the crushed rock. Moreover， the numerical result indicates that the deviatoric stresses and shear strength values increase with confining pressure and block size. The mainly deformation of the crushed rocks is an X shear band formed by sliding and separating along the contact surface under the shear action. In addition， there are different degrees of expansion in the radial direction. The research idea and method of the crushed rock layer in this study will be useful for evaluating thermodynamic stability of the crushed rock embankment of the Qinghai-Tibet Railway.