Copy of Discrete element modelling of geogrid-reinforced railway ballast

铁路道砟在交通荷载作用下劣化。破碎的碎片填满了毛孔，使排水困难。然后必须夯实镇流器，这包括将振动时间插入镇流器并挤压它以将轨枕提升到适当的水平。然而，夯实也会导致颗粒破碎。最终镇流器耗尽，必须更换。5%的废压舱物最终被填埋，每年造成数百万英镑的损失。因此，希望增加压舱物的使用寿命并降低维护成本。为了做到这一点，有必要了解基本的微观力学。压舱物的特性可以用三轴试验来表征；由EPSRC资助的一个大型电池目前正在诺丁汉大学使用。采用单调试验和循环加载试验；循环加载试验用于确定压舱物在交通应力作用下的性能。为了理解粒子力学，可以使用离散元法。在PFC3D程序中，有两个实体：一个球和一个墙。压载物颗粒可以被建模为单个不可破碎的球，或者更现实地说，是许多小球粘合在一起的团块。目的是模拟可破碎压载物的三轴试验，以深入了解其行为。土工格栅通过提供联锁来限制镇流器的变形。这减少了沉降，从而降低了维护成本，延长了镇流器的使用寿命。然而，理想的土工格栅/镇流器几何形状是未知的。这里将使用离散元法来优化系统。结果将是提高对单调和重复载荷下镇流器行为的理解，以及土工格栅的影响，因此可以设计改进的轨道床，从而显着降低维护成本，延长镇流器的使用寿命。

Railway ballast degrades under traffic loading. The broken fragments fill the pores, making drainage difficult. The ballast then has to be tamped, which involves inserting vibrating tines into the ballast and squeezing it to raise the sleeper back to the appropriate level. However tamping also causes particle breakage. Eventually the ballast is spent and has to be replaced. Five percent of spent ballast ends up in landfill, at a cost of millions of pounds per year. It is therefore desirable to increase ballast life and reduce maintenance costs. In order to do this, it is essential to gain an understanding of the fundamental micro mechanics.The behaviour of ballast can be characterised by triaxial testing; a large cell funded by EPSRC is now being used at the University of Nottingham. Both monotonic tests and cyclic loading tests are used; the cyclic loading tests are used to determine the behaviour of ballast under traffic stresses. In order to understand the particle mechanics, the discrete element method can be used. In the program PFC3D, there are two entities: a ball and a wall. A ballast particle can be modelled as a single uncrushable ball, or more realistically, as an agglomerate of many small balls bonded together. The aim is to model the triaxial testing of crushable ballast to gain insight into its behaviour. Geogrids are used to limit the deformation in ballast by providing interlock. This reduces settlement and therefore maintenance costs and prolongs life of the ballast. However, the ideal geogrid / ballast geometry is not known. The discrete element method will be used here to optimise the system.The outcome will be an improved understanding of ballast behaviour under monotonic and repeated loads, and the effect of geogrids, so that improved trackbeds can be designed such that maintenance costs are significantly reduced and ballast has a prolonged life.