Study On Direct Shear Mechanical Characteristics And Reuse Of Recycled Ballast

Ballast wear and breakage were observed under cyclic loading after long-time operation,resulting in a reduction in bearing capacity and drainage.Therefore,it needed periodical ballast cleaning and renewal.On the one hand,a large amount of recycled ballast was produced,causing environmental pollution,meanwhile,the ballasted bed after renewal was fresh-recycled ballast mixture,whose mechanical characteristics was unknown.On the other hand,the level of ballast was gradually rising in recent years and high quality ballast was scarce,resulting in the increasing acquisition cost of ballast.Therefore,further study of recycling ballast has important scientific sense and practical value for the development of green track.For the reuse of recycled ballast,especially the mixture of fresh and recycled ballast,a series of large direct shear tests under different normal stresses were conducted.Meanwhile,the discrete element method was applied on the basis of the 3D scanning and imaging analysis techniques to conduct fresh-recycled ballast mixture DEM model.The compare of the results in model and laboratory can analyze the mechanical characteristics of fresh-recycled ballast mixture from macro and micro views.Conclusions were drawn as follow:a.The strength of ballast increased with the contents of fresh ballast,agreeing with the conclusion that fresh ballast can solidify recycled ballast.For example,under the normal stress of 50kPa,the strength of ballast whose contents of fresh ballast were 50%and 100%,were 143.4kPa and 176.7kPa,increasing 24.0%and 52.9%than that of recycled ballast,respectively.b.The coordination numbers of ballast increased with the contents of fresh ballast,the maximal displacements of ballast decreased with the contents of fresh ballast,the porosities of ballast in measures increased with the contents of fresh ballast.It has been shown that recycled ballast can be compacted by adding fresh ballast,which can improve the bearing capacity and solidify recycled ballast.c.The strength of recycled ballast with geogrid was 160.5kPa,which was higher 38.8%than that without geogrid.The use of geogrid can greatly decrease maximal contact force and enormously increase contact numbers of recycled ballast.It has shown that the use of geogrid can improve the bearing capacity and solidify recycled ballast.