Volume 1, Unit 3 Flashcards
(44 cards)
What are the three soil horizons? What are they made of?
A, B and C horizons.
The “A” horizon is made up primarily of organic materials.
The “B” horizon is made up of different materials, such as sand, gravel, silt, and clay.
The “C’ horizon is rock in its natural state.
Why are “A” horizon soils not used in any phase of construction?
Because they are spongy, drain poorly, and do not compact.
Which soil horizon is the base for all types of pavement construction?
The “B” horizon.
What is another name for the “C” horizon? Why?
It is sometimes called parent material because it is where “B” horizon material comes from.
What is meant by the term plasticity?
The ability of a soil to mold into shapes without cracking or appreciable volume change.
What is a sieve? How are sieve sizes designated?
A screen attached across the end of a cylindrical metal frame; by screen opening size.
Define the term soil gradation.
The distribution of different size groups within the soil sample.
Poorly graded soil may be uniform-graded or gap-graded. What do these terms mean?
In uniform-graded soil, most particles are about the same size; in gap-graded soil, at least one particle size is missing.
What are the two types of stabilization?
Mechanical and chemical.
Why should you mechanically stabilize a subgrade?
To improve the drainage or compaction characteristics of a soil.
What does chemical stabilization do for soil?
It cements the soil into a hard mass, and it changes the soil to make it more suitable for construction.
What are the four main types of chemicals used for stabilization?
Portland cement, bituminous materials, calcium chloride, and lime.
How does calcium chloride increase soil stability?
By controlling moisture content. It absorbs moisture from the air, thus keeping the soil damp.
How much calcium chloride is added to each square yard of soil (one inch deep) to stabilize subgrade?
Half a pound
What pieces of equipment are designed specifically for compaction work?
Sheepsfoot roller, pneumatic-tired roller, and steel-wheel roller.
What type of soil is compacted best when saturated with water?
Sand or sandy gravel.
Besides rollers, what other type of equipment furnishes some form of vibration on soils with low moisture content?
Construction equipment, such as tractors and trucks.
What is the purpose of a blanket or insulating course?
To help prevent plastic soils from working up into the base course and help reduce frost action.
What is used to center the bubble of the bull’s-eye level?
Leveling screws on a triangular footplate.
How is the compensator suspended on the self-leveling level?
On fine, nonmagnetic wires.
When should you start maintaining and caring for your engineer level?
Immediately upon receipt.
Why should most leveling instruments be set up in the shade?
Because the level is highly susceptible to expansion and contraction from direct sunlight.
What are the three cardinal rules of surveying?
Never set up the tripod without finding good footings and setting the legs firmly, never leave the setup instrument unattended, and never straddle the tripod legs.
How is the tripod legs of the leveling instrument set on sloping surfaces?
With two legs downhill.
