Soil Fundamentals

Question 1

What are the different physical properties of parent rock (3)?

Answer 1

Igneous - cool and solidified molten material
Sedimentary - layers of accumulated sediment placed by wind or water
Metamorphic - changed by intense heat or pressure within the Earth

Question 2

What are the two types of weathering soil formation?

Answer 2

Mechanical - frost, thermal, erosion
Chemical - Dissolution, Oxidation

Question 3

What are the two types of soil formation?

Answer 3

Residual - weathers in place
Transported - deposited away from parent rock

Question 4

What is the interaction between shape, size, and gradation of soils?

Answer 4

More angular soils = stronger
Size = friction between particles is the primary force; clay particles have atomic charge controlling force (plastic behavior is controlled by polar water molecules being attracted to clay surface charges)
Gradation = well graded is strongest, then gap, then uniform

Question 5

What is the difference between Plastic Limit and Liquid Limit?

Answer 5

Liquid - soil flows freely under pressure
Plastic - Soil deform under pressure

Question 6

What are the two phases of soil that are able to handle an applied load?

Answer 6

Liquid Phase (pore water (u))
Solid Phase (Soil skeleton (

Question 7

What is the equation for effective stress?

Answer 7

o’ = o - u

Question 8

Plasticity Index?

Answer 8

LL - PL; range of water content where soil behaves plastically

Question 9

Explain how to classify soils using USCS

Answer 9

1. Determine what percentage the soil is of gravel, sand, and fines: 100% - % passing No 4 sieve = gravels; No #200 Sieve = % fines; 100% - % gravels - %fines = % sands
2. Determine if the Cc, Cu will need to be used and if the LL and PL will need to be used.

Question 10

How do granular soils perform in soil layers, frost conditions, and settlement?

Answer 10

High permeability, good backfill, immediate settlement, strength dependent on density

Question 11

How do cohesive soils perform in soil layers, frost conditions, and settlement?

Answer 11

Strength dependent on cohesion, poor foundation materials, compressible over long periods, lose strength when wet or disturbed

Question 12

How well do silts perform in soil layers, frost conditions, and settlement?

Answer 12

Low permeability, hard to compact, very susceptible to frost

Question 13

How well do organics perform in soil layers, frost conditions, and settlement?

Answer 13

Highly compressible, not suitable for foundations