Download - 02 Soil Properties070306
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TDP 2 - Soils Eng. Soil Properties 1
2. Soil Properties
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TDP 2 - Soils Eng. Soil Properties 2
Soil formed in-place is called Residual.
Definitions
Origin of Soil:
Transported soils are described by the method of transportation:
Colluvium is soil that has been transported by gravity (i.e. particles
roll down a steep slope, landslides).
Alluvium is soil that has been transported to its present location
by water.
Aeolian or Eolian is soil that has been transported to its present
location by wind.
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TDP 2 - Soils Eng. Soil Properties 3
Definitions
Origin of Soil:
Glacial tillis soil that has been gouged out of the Earths crust by
ice (glaciers) at one location and dropped at another.
There is usually little or no separation of particles by weight.
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TDP 2 - Soils Eng. Soil Properties 4
Soil Composition
Soil consists of solids
and voids
Solids are mineral
particles
Voids are air and
water between the soilparticles.
s
w
Sample 1
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TDP 2 - Soils Eng. Soil Properties 5
Soil Composition
Volume total = V solid + V air+ V water
Weight total = W solid + W air+ W water
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TDP 2 - Soils Eng. Soil Properties 6
Soil Water
Water content (w) is the percentage of the weightof water to the weight of the dry solids.
Also can be called moisture content
A saturated soil has its voids completely filled withwater. Its water content is denoted by wsat.
Soil below the water table is usually considered to
be saturated.
Dry soil contains only air in the voids.
Wet soils have both water and air
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TDP 2 - Soils Eng. Soil Properties 7
Certain weight relationships have been found to be useful:
Soil Water
Water content is the ratio of the weight of the water to the weight of
the solids.
This ratio multiplied by 100 is the percentage of water content or
moisture content (w).
100
s
w
W
Ww
w = moisture content (%)
Ww= weight of water
Ws = weight of solids
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TDP 2 - Soils Eng. Soil Properties 8
Most soils contain water. Some definitions pertaining to water insoil are as follows:
Soil Water
Dry weight orDry mass is the constant weight of a soil after being
dried in an oven at a temperature of 110 5 C.
Optimum water orOptimum moisture content is the percentage of
water in a soil, based on its dry weight, at which the maximum unit
weight or density is obtained under a given compactive effort and is
denoted by wo.
Dry soils require the addition of considerable water to reach wo.
Soils with water content between dry and saturated are termed wet.
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TDP 2 - Soils Eng. Soil Properties 9
Certain weight relationships have been found to be useful:
Volume-Weight Relationships
Unit weight () or density is defined as the weight per unit volume of asoil.
The total unit weight includes the weight of soil solids and water
divided by the total volume.
V
W
V
WWws
= unit weight
Ws= weight of solids
Ww = weight of water
V = total volume
W = total weight
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TDP 2 - Soils Eng. Soil Properties 10
Certain weight relationships have been found to be useful:
Volume-Weight Relationships
Specific gravity (Gs) is the ratio of the weight of a given volume of the
soil solids to the weight of an equal volume of pure water.
The volume of solids used for determining the specific gravity of solids
does not include any voids.
Typically, Gsis reported for sands and fines.
Values usually range between 2.5 and 2.8, with most falling near 2.65.
High organic content will lead to a lower value, heavy minerals will
give larger values.
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TDP 2 - Soils Eng. Soil Properties 11
Certain weight relationships have been found to be useful:
Volume-Weight Relationships
Units of weight and volume must be consistent.
3ft.in
lbs.in
V
W
In soil engineering, density () and unit weight () are sometimes usedinterchangeably.
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TDP 2 - Soils Eng. Soil Properties 12
The unit weight of soil has specific denotations for each of the
four most frequently used water contents:
Volume-Weight Relationships
Dry unit weight, 0Vwhere, w V
Ws
d
Submerged unit weight is also known as buoyant unit weight (b).
Wet unit weight,
Saturated unit weight,
Submerged unit weight,
0Wwhere,a
V
WWWaws
m
0Vwhere,a
V
WWws
sat
wsatsub
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TDP 2 - Soils Eng. Soil Properties 13
Summary:
Volume-Weight Relationships
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TDP 2 - Soils Eng. Soil Properties 14
100
s
w
W
Ww
w = moisture content (%)
Ww= weight of water
Ws = weight of solids
0Wwhere,a
V
WWWaws
m
or0Vwhere,w
V
Ws
d
1. Moisture Content or Water Content -
2. Wet Unit Weight or Wet Density
3. Dry Unit Weight or Dry Density
1 w
m
d
Three Equations to Know