Performance of Geogrid-Reinforced Recycled Ballast Under Dynamic Loading

Railroad ballast consists of open graded crushed stone used to support railroad track and provide lateral stability. It provides drainable support for the track base and distributes the load to the weaker subgrade below. The issue of ballast performance has become more acute with increased traffic and heavier traffic. Over time ballast degrades and loses strength. Fouling of ballast is one cause of degraded performance and has been a major issue of railway engineering. Fouling can be caused by break down of ballast itself or intrusion of fines from below or from the environment. Fouling material can be removed by undercutting and the remaining ballast can be recycled back on to the right-of-way. It is possible to install a geogrid reinforcement layer in the ballast during an undercutting action. In this experimental study a full-scale railroad section five feet in length was constructed with and without geogrid reinforcement of recycled ballast. The track was dynamically loaded up to approximately 35 psi tie bearing pressure. The reinforced test section with geogrid placed 7 inches below the tie performed better than the unreinforced test section with regard to settlement and fouling of ballast. Settlement of the reinforced test section between the ties and geogrid was substantially less than the settlement of the same portion of the unreinforced test section. The percentage of rock dust and small diameter particles generated by ballast breakdown beneath the ties was observed to be less for the reinforced test section than for the unreinforced test section.