Date post: | 23-Jan-2018 |
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Engineering |
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Geologic definition: Loose surface of the earth as distinguished from solid bedrock or
Soil
Material which nourishes and supports growing plants (includes rocks, water, snow, air).
Soil Mixture of inorganic matter (mineral), organic
matter, water, and air.
Organic Matter
original tissue—twigs and leaves on forest floorhumus—rich brown color in soil decomposed materialAs organisms die, they are attacked by microorganisms: fungi, bacteria, and others.
% Soil components varies:
• Type of vegetation
• Amount of mechanical compaction
• Amount of soil water present.
Why do we study soil? Because It’s A(n)
Great integrator
Producer andabsorber of gases (CO2 and others)
Medium for plant growth
Medium of crop production
Home to organisms(plants, animals and others)
Waste decomposer
Snapshot of geologic, climatic, biological, and human history
Source material for construction, medicine, art, etc.
Filter of water and wastes
Essential natural resource
Medium of heat andwater storage
Weathering forces
• Rocks & minerals break down smaller pieces
– Temperature changes
– Water action
– Plant roots
– Ice expansion
– Mechanical grinding
Temperature changes—heating and cooling of rocks can cause rock to crack into smaller pieces.
Water action--Water soluble minerals dissolve when exposed to water. Some rocks may contain some minerals that are water soluble and only that part of the rock will dissolve
Plant roots—Roots of plants growing in cracks in rocks can widen cracks and break rocks apart.
Ice expansion—If a rock has a crack that can fill up with water, when the water expands when it freezes. This can break rock into smaller pieces.
Mechanical grinding—wind blowing sand across rocks, or glaciers grinding rocks against each other. Example—rock tumbler
1. Silicate Clays (aluminosilicates)
Composed of tetrahedral and octahedral “sandwiches”
Tetrahedron: central cation (Si+4, Al+3) surrounded by 4 oxygens
Octahedron: central cation (Al+3,Fe+2, Mg+2) surrounded by 6 oxygens (or hydroxyls)
• 1000s of tetrahedra and octahedra connect in clay minerals to give:
– Planes of Si, Al, Mg
– Planes of Oxygen, hydroxyl groups
• Sheets combine to form layers
• Layers are separated by interlayer space
– Water, adsorbed cations
DENSITY INDEX OR RELATIVE DENSITY
• The density index is defined as,
ID = (emax – e / emax – emin)
Where,
emax = void ratio in the loosest state
emin = void ratio in the densest state
e = natural void ratio of the deposit
• This term is used for cohesion less soils only.
• When the natural state of the cohesionless soil is in the loosest form,
emax= e.