Track Components – Railway GK for RRB & RPF Exams

Introduction

The permanent way (track) is an engineered structure consisting of rails, sleepers, ballast, fastenings and sub-grade, designed to safely guide and support trains. Every component has a defined load-transfer path and maintenance regime. A sound grasp of these details is essential for all technical & non-technical railway exams.

1. Rails

1.1 Function

• Provide a continuous, level and smooth rolling surface for wheels
• Transmit axle-load to sleepers and ultimately to formation

1.2 Types (Indian Railways)

1.3 Lengths

• Standard length = 13 m (BG), 12 m (MG), 11 m (NG)
• 260 m long-welded rails (LWR) & 780 m continuous-welded rails (CWR) are now standard on new lines

1.4 Wear Limits (per Indian Railways Permanent Way Manual 2021)

• Vertical wear ≤ 6 mm for 60 kg rail
• Side wear ≤ 8 mm
• 5 % loss in sectional weight calls for replacement

1.5 Rail Steel Chemistry

• C 0.55–0.75 %, Mn 0.8–1.1 %, Si 0.1–0.5 %
• UTS ≥ 880 MPa (72 kg/mm²) for 60 kg grade

2. Sleepers (Ties)

2.1 Functions

• Hold rails to correct gauge & inclination (1 in 20)
• Transfer train load to ballast and provide elasticity

2.2 Classification

1. Timber – Sal, Teak, Deodar (life 15–20 y)
2. Steel – CST-9 (9 plates), 90 kg; used in 1950-70
3. Cast Iron – Pot/Plate type (rare now)
4. Pre-stressed Concrete (PSC) – Mono-block, two-block, twin-block

2.3 PSC Sleeper Details (most common)

• Length: 2.60 m (BG), 1.80 m (MG)
• Weight: 285 kg
• Concrete grade: M-60
• High-tensile wire: 5 mm ϕ, 18–20 wires, initial tension 1000 MPa
• Spacing: 65 cm average (BG), 60 cm (MG)

2.4 Sleeper Density

• (n + 3) to (n + 7) sleepers per rail length (13 m)
• → 1540–1660 sleepers/km for BG main line

3. Ballast

3.1 Functions

• Resist longitudinal & lateral forces
• Provide immediate drainage and elasticity
• Distribute load to sub-grade

3.2 Specifications (IRS-GE-1 2016)

• Stone: Igneous (trap, basalt, granite) – 0 % flaky index > 35
• Size:
  • 50 mm to 20 mm (through-screened) for main line
  • 20 mm to 40 mm (retained on 40 mm < 5 %)
• Depth under sleeper: 250 mm (BG), 200 mm (MG)
• Clean ballast cushion: 300 mm below bottom of sleeper for heavy-haul routes

3.3 Ballast Profile

• Shoulder width: 300 mm (minimum)
• Top of formation (TOF) width: 6.85 m (BG, single line)

4. Rail Fastenings

4.1 Elastic Rail Clip (ERC)

• Mark-III free height 200 mm, toe-load 710 kg
• Mark-IV free height 210 mm, toe-load 900 kg (LWR/CWR)
• Pandrol “e-Clip” (imported) 1300 kg toe-load; used in DFC & HSR

4.2 Base Plate & Rubber Pad

• 6 mm thick micro-cellular EVA pad reduces impact by 30 %

4.3 Cotters & Keys

• Keys are driven 1 in 30; split cotter (for fish-plates) is of mild steel 12 mm ϕ

4.4 GM (Gauge-Maintaining) liners used with ERC to adjust gauge ± 1 mm

5. Fish-Plates & Bolts

• Section: 4-hole (52 kg/60 kg) or 6-hole (90 R)
• Material: M-44 steel (0.4 % C)
• Bolt torque: 640 N-m
• Expansion gap: 6 mm at 35 °C for 13 m rail (fish-plated)

6. Sub-Grade & Formation

6.1 California Bearing Ratio (CBR) value required

• ≥ 8 % for BG main line
• ≥ 4 % for MG/NG

6.2 Blanketing Layer (BL)

• 300 mm thick blanket of coarse-grained soil (GP, GW) below ballast to cut capillary rise

7. Historical Milestones

• 1853: First 53 km BB&CI line – 42 lb/yd flat-footed rails on timber sleepers
• 1922: Indian Railway Standard (IRS) rail sections codified
• 1957: Decision to adopt 52 kg rail for all BG routes
• 1990s: Switch to 60 kg 90 UTS rail for Dedicated Freight Corridor planning
• 2006: First 1 km trial of ballast-less track (RHEDA 2000) on Faridabad–New Delhi section
• 2021: Indian Railways approves Head-Hardened (HH) 60 kg rail (350 BHN) for DFC

8. Current Status & Recent Updates

1. Indian Railways procures only 60 kg/52 kg HH rails from SAIL (BSP, DSP)
2. 100 % mechanised deep-screening & tamping with CSM, UNIMAT & UNOMAT machines
3. Complete switch to PSC sleepers: Timber now < 0.5 % of inventory
4. Green Initiatives:
   • Recycled rubber pads from end-of-life tyres
   • Blast-furnace slag ballast trial on 41 km of ECoR
5. Ballast-less Track (BLT):
   • 508 km of Mumbai–Ahmedabad HSR will use Japanese slab-track (RAF-N)
   • BLT standard being finalised by RDSO for 160 km/h semi-urban routes (Draft 2023)
6. Corrosion-resistant Cu–Cr–V alloy rails (SAIL ZINCREX) under trial; targeted life 50 years

9. Summary Tables for Quick Revision

A. Rail Comparison

B. Sleeper Spacing vs Speed

10. Practice MCQs

Last Updated: May 2024