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

1. Transfer and distribute axle loads to formation.
2. Provide elasticity and resilience to the track.
3. Hold sleepers in position – lateral & longitudinal resistance.
4. Provide effective drainage.
5. Absorb vibrations and noise.
6. 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)

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

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)

1. Rationalised Ballast Policy (RB-2022):
   • Zones free to procure ballast from nearest 300 km radius to cut 12 % freight cost.
2. Machine Vision Screening:
   • AI-based cameras at crushers to auto-reject flaky particles; implemented in SWR & ECoR.
3. Tamping-Integrated Ballast Regulators:
   • Now supplied with 3D profile lasers for exact shoulder profiling → 8 % saving per tamping cycle.
4. Synthetic Ballast Trials:
   • Rubber-composite (60 % recycled tyre) blocks on 200 m stretch in WCR; aim to reduce vibration by 30 %.
5. Green Ballast Initiative:
   • MoU with NHAI to use 1 million t annually of muck from highway cutting after washing & grading.
6. Track Circuited Sections:
   • Only electrically clean stone (< 0.5 % conductive minerals) permitted; magnetite-based ballast rejected.

5. Types of Ballast (Used/Proposed)

6. Comparative Table – Ballast Materials

7. 15+ FAQs with Answers

1. The minimum depth of ballast cushion below the sleeper for BG track carrying 22.5 t axle load is

A) 150 mm

B) 200 mm

C) 250 mm

D) 300 mm

2. As per IRS-GE-3, the nominal size of stone ballast for BG is

A) 25 mm

B) 40 mm

C) 50 mm

D) 65 mm

3. The elongation index of ballast should NOT exceed

A) 5 %

B) 10 %

C) 15 %

D) 20 %

4. Which ballast type is electrically preferred in track-circuited areas?

A) River gravel

B) Moorum

C) Sand

D) Broken stone

5. The shoulder width of ballast for LWR track on BG is kept

A) 300 mm

B) 350 mm

C) 400 mm

D) 450 mm

6. Los-Angeles abrasion value for IR stone ballast shall not exceed

A) 5 %

B) 10 %

C) 15 %

D) 20 %

7. The first use of broken stone as ballast in India was recorded around

A) 1853

B) 1870

C) 1890

D) 1905

8. Recycled ballast (RAP) trial with 30 % replacement is presently allowed on

A) High-speed main lines

B) Non-track-circuited lines

C) Bridge approaches

D) Tunnel sections

9. Angle of internal friction (φ) for good stone ballast is approximately

A) 20°–25°

B) 35°–40°

C) 45°–50°

D) 55°–60°

10. Which of the following ballast materials provides the poorest interlocking?

A) Broken granite

B) Quartzite

C) River gravel

D) Sandstone

11. Quantity of stone ballast required for 1 km of BG track with 250 mm cushion is about

A) 1,500 m³

B) 2,000 m³

C) 2,500 m³

D) 3,000 m³

12. The side slope of ballast profile is normally kept

A) 1:1 to 1:1.5

B) 1:2

C) 1:3

D) Vertical

13. Synthetic rubber-composite ballast is being experimented to reduce

A) Maintenance cost B) Vibration & noise C) Electrical leakage D) Rail wear

14. Moorum is NOT preferred on main lines because it has

A) High cost B) High plasticity & poor drainage C) Low availability D) Excessive hardness

15. The latest IRS specification governing ballast is

A) IRS-GE-1 : 2004 B) IRS-T-12 : 2012 C) IRS-GE-3 : 2022 D) RDSO/SPN/2026

16. For NG routes, the minimum ballast cushion is

A) 100 mm B) 150 mm C) 200 mm D) 250 mm

Revision Tip: Remember the “3-5-15” rule – 3 % Deval (attrition), 5 % LA-abrasion (crushing), and 15 % flaky/elongation limits – frequently asked in JE/NTPC technical exams!

Last Updated: January 2026