If you’ve ever wondered about the “rocks” under and around railroad tracks, here’s your answer: It’s called railroad ballast, and it’s critical for keeping tracks stable and in good condition. Installing railroad ballast involves careful planning, selection, site prep and other considerations. Below we will take a closer look at ballast and its importance to railroad infrastructure construction.
Key Functions of Railroad Ballast
Railroad ballast isn’t just laid under tracks for aesthetics. It protects the tracks and, in turn, the thousands of pounds of trains, people and goods passing over them. Essential functions of railroad ballast include:
- Track alignment: Trains can push, pull and distort the rails over time. Ballast helps keep things straight and aligned.
- Load distribution: Tracks (and the ground under them) must support thousands of pounds of train. Ballast evenly distributes a train’s weight to prevent crushing the tracks and underlying soil.
- Drainage: If tracks were laid on soil, rainwater could wash out or weaken the surrounding earth, spelling danger. Ballast stones help water drain away from the tracks and protect the soil nearby.
- Vegetation control: Tree, plant and root growth can affect track drainage and alignment, and interrupt the passage of trains. Ballast helps stem growth and keep tracks clear.
- Vibration absorption: A train’s vibrations may damage tracks or shift the underlying soil. The ballast stones help absorb the vibration and provide protection.
The ballast’s protective properties make it essential to the track’s stability and safety in the long term. The same benefits have also made it a solution in other branches of contracting, from landscaping to road construction.
Common Materials Used for Railroad Ballast
To the naked eye, railroad ballast might look like average gravel, but it’s actually more than that. Not all rocks are created equal, and some don’t make good ballast. Effective ballast is usually made up of:
- Crushed, hard stone like granite or limestone
- Recycled aggregates such as crushed concrete or asphalt
- Industrial byproducts (e.g., steel slag)
Ballast stones, which tend to be about 1-3 in. in size, must be tough and durable to withstand the pressure of thousands of pounds. They need to drain well and endure freezes and thaws that accompany seasonal changes. Importantly, the ballast should be sharp and angular, so the stones will “lock” together when laid. This “locking” will give the ballast its stability to support the tracks.
Site Preparation for Ballast Installation
Incorporating railroad ballast into your construction project requires proper site preparation. This may involve:
- Soil (subgrade) evaluation and stabilization to prepare the ground beneath the ballast/tracks.
- Placement of a geotextile or geogrid to prevent soil from mixing with ballast and protect weak ground areas.
- Grading and slope preparations to ensure ballast allows proper runoff.
- Environmental considerations like stormwater management, erosion control and habitat protection.
The Ballast Installation Process
Railway ballast installation can begin only after site preparation. Ballast must be laid evenly and structured to support the tracks and train weight. Multiple elements must be considered.
- Ballast Depth & Profile Standards
Railway ballast is laid to a specific depth. The minimum depth is usually at least six inches. High-speed or heavy-load tracks often require more. The top layer of ballast will extend outward past the end of the ties. It will then slope downward to balance weight and support drainage.
- Layering
When you layer the sharp ballast locks, they will “catch” or “lock” to hold together snugly and steadily. This will create a stable base for the tracks, but allow enough give to prevent damage from the train’s weight.
- Railroad Tie (Sleeper) Placement
Railroad ties are laid on the ballast’s top layer, with compacted stones piled around them to keep them in place. Filling all gaps ensures an even load and prevents shifting.
- Tamping
Tamping occurs when you place the railroad ties over the ballast. Special machines shake and vibrate the ballast to make it both compact and evenly spread. This helps balance the track and the weight load.
- Track Lining
A final step of the track-laying process is to use track-lining machines to make the tracks perfectly straight and even.
Quality control is essential from site preparation to final track alignment. Contractors should verify that ballast depth, compaction, alignment and other factors meet industry best practices, regulatory standards and project requirements.
Regulatory Standards and Railroad Ballast
Railroad infrastructure is closely regulated at the federal and state levels, and subject to evolving standards. When laying track ballast, you might have to consider guidance from the:
- Federal Railway Administration (FRA), which oversees federal standards for railroad construction.
- Your state’s department of transportation (DoT)—or a similar body—which frequently further regulates rail work within its borders.
- The American Railway Engineering and Maintenance-of-Way Association (AREMA), which provides recommendations on railroad infrastructure construction and maintenance best practices.
You might also need to consider environmental regulations, safety precautions and other minimum standards from various authorities.
Contractor Considerations and Tips
When laying railroad ballast, contractors should keep the following ideas in mind.
- Materials and suppliers: Ballast often must meet minimum quality standards. Only work with reputable suppliers who can prove the quality of their ballast.
- Equipment and crew readiness: Ballast crews must know all steps of the ballast-laying process and be familiar with all equipment.
- Safety protocols: Crews must understand the risks of working near active railroad tracks. Compliance with heavy equipment rules, standard construction-related safety, and environmental precautions are also essential.
- Permitting and regulatory clearance: Certain railroad jobs require approval and permits from state and/or federal authorities. Check your jurisdiction’s requirements during project planning.
Additionally, strictly adhere to material handling and transport requirements, crew scheduling, and equipment sourcing and mobilization. These considerations may impact your timeline and budget. Thorough pre-planning and attention to detail will help ensure your railroad ballast project runs smoothly.
Northern Construction’s Commitment To Strong Rail Infrastructure
Northern Construction has decades of experience in commercial infrastructure across the northeast. Transparent planning, efficient delivery, and scrupulous safety and regulatory compliance enable us to complete all aspects of track construction, including railroad ballast with confidence and professionalism.
Check our portfolio for more information about our work. If you’re interested in partnering with us for your next railroad project, reach out for more information or to receive a quote.