不同边界条件下道砟沉降及受力状态的离散元模拟研究

Influence of boundary conditions on ballast settlement and stress state using DEM

为研究边界条件对循环荷载作用下道砟的力学特性的影响,采用三维扫描技术生成真实形状的道砟颗粒,通过离散元方法模拟单轨枕道砟箱试验。引入侧向周期边界与底部文克勒弹性路基边界以更好地模拟道床的真实受力状态,并与刚性边界道砟箱模拟结果进行对比,探讨侧、竖向边界条件对道床沉降的影响。此外,从细观上分析各边界条件及组合下的道床受力状态,对比周期边界与刚性边界下侧边区域颗粒运动的趋势。研究结果表明:相较于刚性墙边界,周期边界与文克勒弹性路基边界下的道砟沉降量增大、道床弹性模量减小。不同于刚性边界的位移约束,周期边界侧边区域颗粒的位移增大,运动方向更分散,局部孔隙率减小,颗粒平均接触数增大,且平均侧向接触力减少了约41%,表明侧向周期边界处道砟颗粒存在咬合作用且运动方向不受限。在刚性墙模型中引入底部文克勒路基边界后,平均侧向接触力增加了19%,但分布范围没有发生明显变化。针对单轨枕试验的边界条件,考虑侧、竖向边界条件可以更好地模拟道砟的真实受力状态。

In order to study the influence of boundary conditions on the mechanical characteristics of ballast under cyclic loading,3D scan technology was used to generate the real-shaped ballast particle and a discrete element model of box test was established.The lateral periodic boundary and the base Winkler elastic subgrade boundary were introduced to better simulate the real stress state of the track bed,and the simulation results were compared with those of the rigid boundary ballast boxto explore the influence of the lateral and vertical boundary conditions on the settlement of the track bed.Moreover,the stress state of track bed under each boundary condition and combination was analyzed from the micro view,and the particle movement in the side area under periodic boundary and rigid boundary was compared.The results show that compared with the rigid wall boundary,the ballast settlement under the periodic boundary and Winkler elastic subgrade boundary increases and the elastic modulus of track bed decreases.Different from the displacement constraints of rigid boundary,the displacement of particles in the side area of periodic boundary increases,the movement direction is more dispersed,the local porosity decreases,the coordination number of particles increases,and the average lateral contact force decreases by about 41%,indicating that there is interlocking between ballast particles at the lateral periodic boundary,and the movement direction is not limited.Considering the Winkler subgrade boundary into the rigid boundary model,the average lateral contact force increases by 19%,but the force distribution does not change significantly.For the boundary conditions of single sleeper test,considering the lateral and vertical boundary conditions can better simulate the real stress state of ballast.