Ballast Types
Ballast Types – Railway GK for RRB & RPF Exams
Ballast is the granular material (usually broken stone) laid below and around sleepers to transmit load from the sleeper to the formation, provide lateral and longitudinal stability, and facilitate drainage. The choice of ballast type directly affects track life, riding quality and maintenance effort.
1. Detailed Technical Information
1.1 Functions of Ballast
- Transfer and distribute axle loads to formation.
- Provide elasticity and resilience to the track.
- Hold sleepers in position – lateral & longitudinal resistance.
- Provide effective drainage.
- Absorb vibrations and noise.
- Facilitate maintenance by allowing packing/lining.
1.2 Ideal Ballast Properties
- Hardness: ≥ 17 on Mohs’ scale (Deval attrition ≤ 3 %).
- Angularity: 2.85–3.0 (flakiness index ≤ 15 %, elongation ≤ 15 %).
- Strength: Aggregate crushing value ≤ 30 % (IRS-GE-3).
- Gradation: Nominal size 50 mm (retained on 40 mm ≥ 40 %, passing 20 mm ≤ 5 %).
- Durability: Los-Angeles abrasion ≤ 5 %.
- Cleanliness: Clay lumps ≤ 1 %, dust ≤ 2 %.
- Non-porous & free from weathering.
1.3 Thickness Standards (Indian Railways)
| Track Type | Minimum Ballast Cushion (below bottom of sleeper) |
|---|---|
| BG (≤ 20 t axle load) | 250 mm (200 mm after compaction) |
| BG (> 20 t axle load, DF) | 300 mm |
| MG | 200 mm |
| NG | 150 mm |
| LWR track (BG) | Extra 50 mm shoulder ballast on cribs |
1.4 Ballast Profiles (BG)
- Shoulder width: 350 mm (450 mm for LWR).
- Side slope: 1:1 to 1:1.5.
- Crib ballast: 25 mm below sleeper top for wooden sleepers; 15 mm below for concrete sleepers.
2. Important Facts, Figures & Specifications
| Specification | Value |
|---|---|
| IRS-GE-3 (latest 2022) | Indian Railway’s ballast specification |
| Nominal size | 50 mm |
| Minimum compacted density | 1.6 t/m³ |
| Void ratio (loose) | 0.35–0.40 |
| Angle of internal friction (φ) | 35°–40° |
| Modulus of sub-grade reaction (K) | 0.25–0.35 N/mm³ |
| Life of good stone ballast | 15–20 years (traffic dependent) |
| Quantity per km (BG, 250 mm cushion) | ≈ 2,500 m³ (≈ 4,000 t) |
3. Historical Developments
- 1853: First passenger train – locally available laterite & river gravel used as ballast.
- 1890: Adoption of broken stone (trap & granite) on the GIP Railway.
- 1935: Indian Railway Standard (IRS) first issued for stone ballast gradation.
- 1957: Mechanical crushers introduced; specifications revised to limit flaky aggregates.
- 1986: IRS-GE-3 unified all previous ballast circulars.
- 1995: 40 mm size experimented on high-speed (140 km/h) Rajdhani route; reverted to 50 mm due to pumping.
- 2006: 300 mm cushion mandated for DFC routes (32.5 t axle).
- 2019: Geo-textile layer below ballast piloted on Palwal-Mathura (NCR).
- 2021: Recycled ballast (RAP) trials started in SCR; 30 % replacement allowed in non-track-circuited lines.
4. Current Status & Recent Updates (2022-24)
- Rationalised Ballast Policy (RB-2022):
- Zones free to procure ballast from nearest 300 km radius to cut 12 % freight cost.
- Machine Vision Screening:
- AI-based cameras at crushers to auto-reject flaky particles; implemented in SWR & ECoR.
- Tamping-Integrated Ballast Regulators:
- Now supplied with 3D profile lasers for exact shoulder profiling → 8 % saving per tamping cycle.
- Synthetic Ballast Trials:
- Rubber-composite (60 % recycled tyre) blocks on 200 m stretch in WCR; aim to reduce vibration by 30 %.
- Green Ballast Initiative:
- MoU with NHAI to use 1 million t annually of muck from highway cutting after washing & grading.
- Track Circuited Sections:
- Only electrically clean stone (< 0.5 % conductive minerals) permitted; magnetite-based ballast rejected.
5. Types of Ballast (Used/Proposed)
| Type | Material | Suitability | Remarks |
|---|---|---|---|
| 1. Broken Stone (Granite, Trap, Quartzite) | Best for high-speed & heavy axle routes | Preferred IR ballast | |
| 2. Gravel / River Pebbles | NG routes, yards | Round shape → poor interlocking | |
| 3. Ashes / Cinders | Ash pit discharge areas | Light, corrosive, banned on main lines | |
| 4. Sand | Temporary diversion | Only emergency, needs frequent relaying | |
| 5. Moorum | Approach tracks in formation stage | Lateritic soil + gravel; high plasticity | |
| 6. Blast Furnace Slag | Pilot on ECoR (2023) | Porous, good drainage; need metal detection | |
| 7. Rubber-Composite | R&D, WCR (2023) | Vibration dampening; cost 3× stone | |
| 8. Geo-synthetic Reinforced Ballast | DFC (planned 2025) | Extends maintenance cycle by 1.5× |
6. Comparative Table – Ballast Materials
| Property | Broken Stone | Gravel | Moorum | Slag |
|---|---|---|---|---|
| Crushing strength | Very high | Medium | Low | High |
| Interlocking | Excellent | Poor | Fair | Good |
| Drainage | Very good | Good | Poor | Excellent |
| Availability | Wide | Rivers | Local | Steel plants |
| Cost (₹/m³) | 800-1000 | 400-500 | 200-300 | 600-700 |
| Suitability | A-1 | C | D | B (with metal removal) |
7. 15+ MCQs with Answers
Q1. The minimum depth of ballast cushion below the sleeper for BG track carrying 22.5 t axle load is
250 mm ✔ (300 mm for > 25 t axle/DF routes)
Q2. As per IRS-GE-3, the nominal size of stone ballast for BG is
50 mm ✔
Q3. The elongation index of ballast should NOT exceed
15 % ✔
Q4. Which ballast type is electrically preferred in track-circuited areas?
Broken stone (non-conductive) ✔
Q5. The shoulder width of ballast for LWR track on BG is kept
450 mm ✔
Q6. Los-Angeles abrasion value for IR stone ballast shall not exceed
5 % ✔
Q7. The first use of broken stone as ballast in India was recorded around
1890 ✔
Q8. Recycled ballast (RAP) trial with 30 % replacement is presently allowed on
Non-track-circuited lines ✔
Q9. Angle of internal friction (φ) for good stone ballast is approximately
35°–40° ✔
Q10. Which of the following ballast materials provides the poorest interlocking?
River gravel ✔
Q11. Quantity of stone ballast required for 1 km of BG track with 250 mm cushion is about
2,500 m³ ✔
Q12. The side slope of ballast profile is normally kept
1:1 to 1:1.5 ✔
Q13. Synthetic rubber-composite ballast is being experimented to reduce
Vibration & noise ✔
Q14. Moorum is NOT preferred on main lines because it has
High plasticity & poor drainage ✔
Q15. The latest IRS specification governing ballast is
IRS-GE-3 : 2022 ✔
Q16. For NG routes, the minimum ballast cushion is
150 mm ✔
Revision Tip: Remember the “3-5-15” rule – 3 % Deval, 5 % LA-abrasion, 15 % flaky/elongation limits – often asked in JE/NTPC CBT.
BETA
