Engineering properties of Soil

Question 1

Soil

Answer 1

Loose un-compacted material that is not rock
Soils are the products of weathering of rocks. They may be sedentary, produced by weather in situ, or they may be transported, with the material having been moved in from somewhere else.

Question 2

Weathering

Answer 2

Defined as the physical breakdown (disintegration) and chemical alteration (decomposition) of rocks and minerals at or near surface. Most rocks exposed on the surface suffer from disintegration or decomposition due to:

1. Atmosphere
2. Water and ice
3. Living organisms

Question 3

Mechanical weathering

Answer 3

Disintegration by the atmosphere (wind), water/ice and living organisms occurs by the physical breaking down of the rock into smaller particles or the abrasion and wearing away of rock

Question 4

Chemical weathering

Answer 4

Decomposition refers to the chemical breakdown of rocks- usually by the chemical change of the constituant minerals. With the breakdown certain of the components will be taken into solution and removed thereby dissolving the mineral
Main causes:
1. Oxidation- chemical combination of oxygen with substance
2. Hydrolysis- Change by the uptake of water
3. Carbonatisation- changes by reaction with dissolved carbon dioxide

Question 5

Soil properties

Answer 5

Properties of soil depends on their composition and moisture content
Density of soil is the mass of volume of soil compared to mass of equal volume water. Difficult to measure because is comprised of loose granular material and density is thus dependent on porosity or degree of compaction
Moisture content has big influence on property- consists of sorbed water which is capillary water in pore spaces and has effect of holding particles together by surface tension. Capillary water depends on grain size and porosity
Cohesion depends on electrostatic forces (van der waals )

Question 6

Strength of soil

Answer 6

Grain size, sorting and moisture influence engineering behaviour of soils. Larger particles higher strength, mixture of particle size strongest
Strength of soil is due to friction when they slide roll and rotate. Friction is influenced by grain size distribution and shape
Water content also influence strength, sorbed water on grain boundaries reduce friction
Principle minerals in clay soil influence its engineering behaviour