3.1 Origin and classification of rocks and soils

Question 1

Define soil for geological engineering

Answer 1

Soil is any uncemented or weakly cemented accumulation of particles formed by the weathering of rocks and the void space between the particles containing water or air.

Question 2

Types of weathering

Answer 2

• Mechanical (physical): Results in rock being broken down into smaller particles that have the same mineralogical composition as the parent rock
• Chemical: caused by rainwater reacting with the mineral grains in rocks

Question 3

Two types of soils

Answer 3

Residual soils: formed by weathered products at their place of origin
Transported soils: moved from place of origin (more common)

Question 4

Why are clays different that sands or gravel?

Answer 4

They are not just very small rocks

Question 5

Clay mineralogy

Answer 5

Is what the clay is composed of on a molecular scale

Question 6

Explain two ways to determine particle size distribution

Answer 6

Mechanical analysis: coarse grains - % Gravel, Sand, Fines
Hydrometer analysis - % Silt vs Clay

Question 7

Dispersive soils

Answer 7

high erosion potential

Question 8

Well graded vs poorly graded

Answer 8

Well graded: means poorly sorted
Poorly graded: Very well sorted

Question 9

Mechanical weathering mechanisms and soils

Answer 9

Alluvial soils: Moved or transported by running waters
Glacial soils: Moved or transported by glaciers
Lacustrine soils: Deposited in lakes
Marine soils: Deposited in the ocean
Aeolian soils: Deposited by wind
Colluvial soils: deposited or transported by rock fall or gravity

Question 10

Atterberg limits

Answer 10

How does soil behave under different moisture contents

Question 11

Types of Atterberg limits

Answer 11

Shrinkage limit (SL)
Plastic Limit (PL)
Liquid Limit (LL)
Plasticity Index (PI)