1. Lecturer: Dr. Frederick Owusu-Nimo
Civil Engineering Department College of Engineering Course: Soil and Rock Mechanics (CE 260)
Lecturer: Dr. Frederick Owusu-Nimo

2. What is Soil Mechanics? Why Soil Mechanics?
It is a discipline in Civil Engineering that applies principles from engineering mechanics (Basic Mechanics) and Elementary fluid mechanics to determine or predict the behavior of soil.
Why Soil Mechanics?
Whatever structure we build, the ultimate foundation or support is the Earth
Need to study the behavior of the soil and its interactions with the structure, to ensure its stability and safety of the people who use it.

3. Soils as Foundation Material
What supports these structures?

4. Soils as Foundation Material
Proper functioning of these structures require well designed foundations
A foundation is the material, which provides satisfactory and economical support for the structure.
Foundation includes both the soil under the structure and intervening load carrying members

5. Soils as Foundation Material
Location of competent soil material
Shallow Foundation
Deep Foundation

6. Soils as Construction Material
Road pavement
Earth dam
Use of Soil as construction material requires
Selection of appropriate soil type (Why?)
Selection of appropriate method of placement
Control of actual placement

7. Soil in Slope and Excavations
Important to carry out stability analysis of excavations and slope of embankments to prevent failures and disasters

8. Earth Retaining and Underground Structures
Design against lateral or earth pressures on retaining walls
Design against pipe crushing and pipe sag due to foundation settlement or failure
Braced Excavations- Subjected to lateral stresses
Buried Pipeline – subjected to stresses from overburden

9. Solution of Soil Engineering Problem
Solving any soil-engineering problem requires
Knowledge in soil mechanics and engineering geology
Experience (including case studies)
Economics (to allow selection of best solution among possible ones)

10. Formation of Soils
Important to determine engineering properties of soils
​Engineering properties of soils influenced by how the soil is formed
Knowledge of the soil forming process greatly facilitate engineering classification of soils
How are Soils formed?
Soils are formed by disintegration of rocks through the process of weathering
Physical (Mechanical) Weathering
Chemical Weathering

11. Physical Weathering
Break down of parent rock by mechanical processes such as abrasion, expansion and contraction
Factors
Temperature changes
Freezing and thawing of water in cracks
Rainfall, wind and sediment transport
Soils produced maintain the same chemical composition (crystal structure) as the parent rock

12. Chemical Weathering
Involves break down of rock atomic structure, and the changing of its mineral from one form to another
It results from reactions of rock minerals with:
Oxygen (Oxidation),
Water (Hydrolysis),
Alkaline/acidic materials dissolved in water (Dissolution)

13. Chemical Weathering These processes can
Lead to ‘rusting’ of iron rich rocks
Increase the volume of materials e.g. clay mineral absorbing water and expanding
Dissolve part of rock matter creating voids in them e.g. caves in rocks
Physical weathering also enhances chemical weathering
Soils produced have their physical and chemical characteristics modified

14. Types of soils based on rock type
Soil Formed
Igneous Rocks
Granite
Silty Sands, Sandy Silts with some clay
Basalt
Clayey Soils
Sedimentary rocks
Shale
Clays and silts
Sandstone
Sandy Soils
Limestone
Fine grained soils
Metamorphic rocks
Gneiss
Schist
Silty sand soils
Slate
Marble
Fine grained Soils
Quartzite
Coarse grained soils ( Sand and gravels)

15. Types of soils based on method of formation
Sedimentary soils (Transported Soils)
Refers to soils formed at one location, transported and deposited at another location
Agents of transportation
Wind
Water
Gravity

16. Formation of Soils Residual soils Residual Soil Profile?
Soils formed and accumulated at same location (They are not transported)
Residual Soil Profile?
Parent rock entirely altered in mineral form near the surface
Alteration lesser at greater depth

17. Constituent of Soils Primary rock minerals Clay minerals
Pieces broken from parent rock
Sizes greater than mm
Clay minerals
Mainly products of chemical weathering
Particle sizes less than mm
Basic clay minerals
Kaolinite
Illite
Montmorillonite