05 Ballast (Railway Engineering Lectures هندسة السكك الحديدية & Dr. Walied A. Elsaigh)

1. Dr. Walied A. Elsaigh
welsaigh@ksu.edu.sa
Asst. Prof. of Civil Engineering
Jumada’-I 1437H
CE 435
Railway Engineering
Ballast

2. Text Book
Railway Engineering,
Satish and Agarwal,
2nd edition, 2013
Chapter 8
Page 142-155

3. What is Ballast ?
Layer of broken stones, gravel or any granular material
placed and packed below and around sleepers mainly to
distribute load from sleeper to formation.

4. Functions of Ballast
 Provides level and hard bed for the sleepers.
 Holds the sleeper in position during passage of train
(lateral and longitudinal stability of the track).
 It transfers and distribute the load from sleepers to larger
area information.
 It provides resilience and elasticity to the track
(leads to comfort and riding quality).
It provides proper and effective drainage to the track.

5. Types of Ballast
Several types are used around the world but mainly
crushed stones.
In KSA: crushed limestone is used for most of the track
lines especially in the central region (Riyadh area).
SAR engineer mentioned: they are getting cases where
limestone ballast stones chemically bonds to each other
resulting in the track losing its elasticity.<<class discussion>>

6. Requirements for Good Ballast
 It should be tough and wear resistant (LA <30%)
 Should be cubical with sharp edges.
 Non porous and non water absorbent.
Particle size distribution that allows for good drainage.
 It should be cheap.

7. Ballast Gradation

8. Ballast Cleaning
Ballast is subject to pulverization from loading and
unloading as trains pass over, thereby generating fine
particles that clog the ballast.

9. Ballast Minimum Depth
Note: AREMA calculates it differently, using
pressure on the sleeper (Talbot formula).
Depth of Ballast (d) = Sleeper spacing – Sleeper width
2

10. Ballast Construction
https://www.youtube.com/watch?v=T4aALRa9jjg

11. Ballast & sub-ballast
cross-section
* AREMA recommended practice.
Can you calculate the volume of ballast and sub-ballast
required to construct 1 km of KSA railway track?.

12. Recap
 Ballast and sub-ballast are the final stages in load
distribution.
 Ballast has a critical role maintaining longitudinal and
lateral stability of track.
 Ballast and sub-ballast must provide adequate
drainage.
 Gradation: AREMA, LA<30, cubical shape

13. Assignment
• Similar to highway base material
• Fine grained
• Compact Well
Consult AREMA: Provide the
specifications of sub-ballast.
Handout: Comparison between ballasted
and ballastless railway track