CTB Ballast & Subgrade Preparation

Question 1

What is the primary function of ballast in railroad track construction?

Accepted Answer

To distribute loads, provide drainage, and maintain track position

Answer

To provide a decorative appearance for the track right-of-way

Answer

To prevent rail from expanding due to thermal changes

Answer

To lubricate the interface between rails and wheel flanges

Question 2

Which material is the preferred choice for mainline railroad ballast?

Accepted Answer

Granite or trap rock (crushed stone)

Answer

River sand

Answer

Gravel and river cobbles

Answer

Recycled concrete aggregate

Question 3

What term describes ballast that has become contaminated with fines and degraded particles, reducing its drainage capacity?

Accepted Answer

Fouled ballast

Answer

Spent ballast

Answer

Depleted ballast

Answer

Soft ballast

Question 4

What is the subgrade in railroad track construction?

Accepted Answer

The prepared native soil or engineered fill on which the track structure is built

Answer

The layer of ballast directly under the ties

Answer

The layer of asphalt placed between ballast and native soil

Answer

The concrete base used under slab track systems

Question 5

What is the purpose of a subballast layer in railroad track construction?

Accepted Answer

To separate ballast from subgrade and improve load distribution and drainage

Answer

To anchor rail spikes firmly into the track bed

Answer

To support overhead electrical wiring systems

Answer

To provide a walking surface for track maintenance workers

Question 6

What is 'pumping' as it relates to railroad track subgrade problems?

Accepted Answer

The upward ejection of wet, fine-grained subgrade material through ballast when trains pass

Answer

Using water jets to clean fouled ballast in place

Answer

Installing drainage pumps along the track right-of-way

Answer

Spraying water on ballast to aid compaction during installation

Question 7

What type of soil is generally considered most problematic as a subgrade material for railroad track?

Accepted Answer

Expansive high-plasticity clay (CH)

Answer

Well-graded gravel (GW)

Answer

Clean poorly-graded sand (SP)

Answer

Dense limestone bedrock