Ballast is a granular and porous material, typically composed of crushed stone, used to support railway rails and sleepers, distribute loads to the ground, and ensure the continuity of track geometry.

Function of Ballast in the Railway System

In railway infrastructure, ballast fulfills the following essential functions:

Load Distribution: Transfers loads received via rails and sleepers to a wider area and to the substructure
Vibration Damping: Absorbs dynamic forces during train passages, ensuring ride comfort
Drainage: Facilitates the removal of rainwater and groundwater from the track
Preservation of Track Geometry: Keeps track gauge and alignment stable

Technical Properties of Ballast

A high-quality railway ballast should possess the following characteristics:

Grain Size: Should be between 22 mm and 63 mm (in compliance with TS EN 13450)
Compressibility: Should have a low compression rate and maintain its form under dynamic loads
Hardness: Must resist high pressure and not crumble easily
Water Absorption Rate: Should be low to avoid hindering drainage
Edge Angle: Angular, irregular grains enhance interlocking through high friction
Contamination Ratio: Fine materials should be less than 1%
Ease of Maintenance: The ballast layer is renewable and rearrangeable

Material Type Used

Railway ballast is generally produced from hard rocks known as crushed stone. Preferred rock types include:

Basalt: The most commonly used ballast type in Türkiye; features high strength and low water absorption
Granite: Chosen for its hardness and abrasion resistance
Andesite: Cost-effective and possesses sufficient physical properties
Diabase and Quartzite: Usable if locally available
Limestone: Not considered suitable by TCDD due to its soft structure and low abrasion resistance

Layer Structure and Thickness

The ballast layer in the track superstructure is divided into two:

Sub-ballast (sub-base layer): Laid to form a smooth surface for ballast placement; thickness is typically 10–15 cm
Top Ballast: Fully surrounds the sleepers; in main lines, its thickness is 25–35 cm. In high-speed train lines, this is increased

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Use and Standards in Türkiye

TCDD uses the TS EN 13450 standard and its internal technical specifications for ballast procurement and installation. Production is generally carried out by TCDD Stone Crushing Facilities, and the suitability of quarries is evaluated based on technical reports.

The 2023 TCDD Network Statement provides detailed explanations regarding ballast procurement and maintenance activities. Particularly in track renewal works, the reuse of old ballast through screening has gained importance for sustainability.

Advantages

Long Lifespan: High-quality ballast can be used for decades with proper maintenance
Modularity: Damaged sections can be easily removed and re-laid
Cost-effectiveness: Offers a cost advantage when supplied from domestic quarries
Ease of Application: Can be laid and compacted manually or by machine

Disadvantages

Dust Accumulation: Fine materials can accumulate over time, reducing drainage
Displacement Risk: Ballast may shift under heavy train loads
Frequent Maintenance Requirement: Requires regular levelling, screening, and reinforcement over extended use

Ballast is one of the oldest and most fundamental components of the railway superstructure. With its essential functions in load transfer, track stability, and drainage, it directly affects the performance of railway lines. In Türkiye, high-standard production is carried out using primarily basalt-based crushed stones, and track safety and comfort are ensured through practices compliant with TCDD’s technical specifications.

Ballast