Soil Classification

Question 1

What are the 5 main groups of soil?

Answer 1

Gravel, sand, silt, clay & organics

Question 2

What size separates coarse-grained soils from fine-grained soils?

Answer 2

< 0.075mm (#200 sieve)

Question 3

What is soil cohesiveness?

Answer 3

How well it sticks together. Coarse tend to not be cohesive, fines are usually cohesive.

Question 4

What is “specific surface”?

Answer 4

Specific surface = surface area/mass

Clay has the highest specific surface (20,000 - 8,000,000 cm2/g)!

Question 5

What does USCS stand for?

Answer 5

Unified Soil Classification System

Question 6

What is the max size of clay?

Answer 6

< 0.002mm

Question 7

Using USCS, what constitutes a fine-grained soil?

Answer 7

A sample that has more than 50% passing the #200 sieve.

Question 8

How would you describe a clay sample with liquid-limit > 50%

Answer 8

Fat Clay (CH)

Question 9

What kind of soil is MH?

Answer 9

Elastic Silt

Question 10

What kind of soil is CL-ML?

Answer 10

Silty clay

Question 11

What kind of soil is GW?

Answer 11

Well-graded gravel

Question 12

What kind of soil is SP?

Answer 12

Poorly-graded sand

Question 13

What kind of soil is SW-SM?

Answer 13

Well-graded sand with silt

Question 14

What kind of soil is SM with >15% gravel?

Answer 14

Silty sand with gravel

Question 15

What is the formula for Coefficient of Uniformity (Cu)?

Answer 15

Cu = D60/D10

Question 16

What does a low value for the Coefficient of Uniformity (Cu) suggest?

Answer 16

A poorly-graded soil, since D60 will be close to D10.

Question 17

What is the typical range of values for the Coefficient of Curvature (Cc)?

Answer 17

1 < Cc < 3

…A value outside of this would suggest a gap-graded soil.

Question 18

What kind of soil is OH?

Answer 18

Organic with high plasticity.

Question 19

What is the worst soil?

Answer 19

Pt (peat)… Even worse than OH and CH

Question 20

What are some classification systems?

Answer 20

USCS and Visual-Manual are what we use in this course.

Others are AASHTO, CFEM, USDA, etc.

Question 21

How do you quantify soil types using the UCSC system?

Answer 21

Particle Size Distribution and the Atterberg Limits

Question 22

What are the descriptor for coarse-grained soils using the Visual Manual method?

Answer 22

Angularity, shape, moisture, cementation, PSD, particle sizes and colour.

Question 23

What are the descriptors for fine-grained soils using the Visual Manual method?

Answer 23

Plasticity, dry-strength, dilatancy, consistency, moisture, colour

Question 24

What is determined by the dilatancy test?

Answer 24

How quickly water is removed from soil when shaken

Question 25

What are some ways to tell between silt and clay?

Answer 25

• Silt is gritty while clay is smooth
• Silt washes away while clay sticks
• Silt responds to dilatancy while clay has a slow/no reaction
• Silt powders when dry while clay is hard to break when it dries
• Silt is difficult to roll into string, while clay can be rolled out without breaking.

Question 26

A soil with large particles in comparison to a soil with small particles has what benefits?

Answer 26

Soil w/ large particles will usually be:

• stronger
• less compressible
• more permeable (allows water to flow through it)
• less frost susceptible

Question 27

What are some assumptions when using hydrometer (Stokes’ Law)?

Answer 27

• particles are spherical
• particles are smooth
• no interference between side walls and particles
• all particles have the same Gs
• flow is laminar

Question 28

Which Group Symbol (i.e. MH) is the best to use as a base course for pavement?

Answer 28

GW (well-graded gravel)… Best soil in general.