Engineering geology and Geohazards Lecture 1: The Nature of Soil

Question 1

Define what soil is

Answer 1

Soil (In a geological context) is structural material.
Meaning how soil responds to different weight conditions.

Question 2

What is the origin of soil/soils?

Answer 2

Soils are particles of mineral matters which have originated from the weathering of a parent rock.

Question 3

What are the two main weathering processes?

Answer 3

Physical/Mechanical:
-Water or wind affecting rocks
-Temperature affecting rocks

Chemical:
-The Atmosphere interacting with rocks, altering the chemical composition of the rocks. Causes decomposition in rocks.
-E.g. oxidisation, carbonation

Question 4

How does compacted soil become cemented?

Answer 4

When soil is compacted, they become cemented if there is cementing agents present such as iron oxide and calcite .

Once the soil is cemented it becomes sedimentary rock.

Question 4

How do soil deposits become compacted?

Answer 4

Soil deposits may become overburden with extra sediment layers causing extra weight. Causing the first layer of sediment to compact.

(Meaning that the amount of voids/pore space in the soil is reduced.)

Question 4

Define a transportation agent

Answer 4

Transportation agents (e.g. wind or water) move the sediment weathered off the parent rock and deposit them in different places.

Once this happens the deposited weathered rock becomes layers of sediment.

Question 4

Define erosion (in an engineering geological context)

Answer 4

Erosion is when during transportation the weathered rock can be further broken down.

Question 5

What are the categories of soil?

Answer 5

Residual soils
Water transported/deposited soils
Gravity soils
Wind blown soils
Glacial soils
Organic soils
Fill materials
Made ground