02 soil properties070306

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TDP 2 - Soils Eng. Soil Properties 1

2. Soil Properties


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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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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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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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Soil Composition

Volume total = V solid + V air+ V water

Weight total = W solid + W air+ W water


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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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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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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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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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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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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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The unit weight of soil has specific denotations for each of the

four most frequently used water contents:


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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Summary:



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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

02 soil properties070306

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