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

Ballast distributes vertical loads from ties to the subgrade, provides drainage, and anchors the track against lateral and longitudinal movement.

Question 2

Which material is the preferred choice for mainline railroad ballast?

Accepted Answer

Granite or trap rock (crushed stone)

Answer

Crushed granite or trap rock provides angular particles that interlock well, resist degradation under repeated loading, and allow excellent drainage.

Question 3

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

Accepted Answer

Fouled ballast

Answer

Fouled ballast contains excessive fines that fill void spaces, reducing drainage capacity and load-bearing performance below acceptable standards.

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 subgrade is the prepared natural ground or compacted fill that forms the foundation of the track structure below the ballast and subballast layers.

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

Subballast acts as a filter and separator between ballast and subgrade, distributes loads more uniformly, and prevents subgrade material from migrating upward into the ballast.

CTB - Certified Track Builder Practice Test

CTB - Certified Track Builder Practice Test

CTB Ballast & Subgrade Preparation