Ballast (usually crushed stone), as it is known, is a very important part of railway infrastructure and railway maintenance. Although it may just look like plain gravel, this stone plays a vital role in acting as a support base for the ties and rails, as well as allowing for proper drainage of water away from the rails (which is why the stone should always be sloped downward and away from track). If you are wondering how such a term came to define the stone which supports the track structure, it has its roots dating back to early times when stone was used as ballasting for sailing ships. Of course, while crushed stone (often limestone or quartz) is the aggregate of choice for today’s railways, in years past everything from slag to cinders has been used (always resourceful years ago railways would use whatever they could find). Some light density branch lines would appear jet black as nothing but burnt coal cinders were used to ballast the route. In any event, ballast must regularly be cleaned or added, as when dirt and grime builds up within the rock it reduces its ability to properly drain water. Ballast also acts as a support base for the track structure, giving it strength and rigidity, but also allowing for flexibility when trains pass over. Limestone or quartz is often most used as ballasting because it is a hard stone that will lock together providing for extra strength. According to Brian Solomon’s book Railway Maintenance, The Men and Machines That Keep the Railroads Running , today’s trains can exert a force of 100 psi when passing over track and the stone used for ballasting must be able to withstand this constant abuse. For history’s sake ballast has its earliest beginnings as simple limestone blocks, which actually sometimes pulled double duty as both the support base and track structure. In the 1840s true ballast, or crushed stone, as we know it today began to be widely used and was soon found to be far superior to the old method. One often forgotten aspect of the ballasting system is what is known as sub-ballast or sub-grade. This layer of crushed stone or even pavement, as some railways today now use, acts as a moisture barrier and added support system for the track structure above (including the rails, ties, and ballast). It is always the first component of the track structure to be laid down and is a very important, unseen component. If the track did not have a sub-ballasting system, or very poor one at best, the rails and ties would eventually become water-logged and fail (causing a derailment, or worse, a washout). According to Brian Solomon’s book Railway Maintenance, The Men and Machines That Keep the Railroads Running , today the typical layout for a well-ballasted track system is stone lined to the top of the ties protruding roughly 14 inches to either side, tapering away on a “3-to-1” slope to an eventual distance of 9 feet, 10 inches from the center-of-track with the stone being about one-foot deep below the bottom of the ties. Pretty technical stuff for something that looks so simple! If you ever happen to take a closer look at a well-maintained right-of-way be sure and notice how the ballast system works, aside from the stone and technical layout. To either side of the track below the ballast you will notice a well-groomed ditch that carries away all of the water which drains from the track structure. Also pay attention to the rails and ties. If the system is properly ballasted and maintained no water will be anywhere near either, as will weeds and other foliage. It’s hard to believe that simple crushed stone plays so many vital roles as part of the track structure.
If you have a railway infrastructure to maintain, you can get all the help you need for railway maintenance or track maintenance from Pearson’s Engineering Services.
