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01/03/2012
1
SOIL COMPOSITION
SOIL COMPOSITION� Generally soil can be divided to three components in
natural occurrence
� This separation know as three phase systems or three phase diagram
� It consists of soil solids, water and air
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Soil components in natural occurrence
Volume-Weight relationships� As a result from 3 phase diagram several relationship
were produce
� This relationship known as volume weight relationships.
� Refer to 3 phase diagram
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Relationship equations
V = Vs +Vv ( eq. 1)= Vs + Vw + Va
whereVs = volume of soil solidsVv = volume of voidsVw = volume of water in the
voidsVa = volume of air in voids
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Relationship equations
W = Ws + Ww ( eq. 2)
where,Ws = weight of soil solidWw= weight of waterWa = zero (negligible)
Water content@ Moisture content
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Void ratio
The ratio of the volume of voids Vv to the volume of soil solid Vs
Porosity
The ratio of the volume of voids, Vv to total volume, V expressed as either a decimal or a percentage.
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Relationship between void ratio and
porosity
e = Vv = Vv = (Vv/V ) = nVs V – Vv 1 – (Vv/V) 1- n
n = e1 + e
Degree of saturation
The ratio of the volume of water, Vw to the volume of voids, Vv. It’s commonly in percentage
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Unit weight
The weight of soil per unit volume
Moist unit weight
Dry unit weight
Relationship between dry unit and bulk unit weight
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Derivation –cont’d
� So what is the different between unit weight and density?
� Unit Weight is influence by gravity forces while mass isn’t (Unit Weight=Weight/ Volume while Density= Mass/Volume)- Weight = Mass x Gravity acceleration
� So we can use the similar equations on related calculation if there is only density
Specific Gravity
Specific gravity can be determined as a ratio of the unit weight of the soil material to the unit weight of water (9.81 kN/m3 or density 1000 kg/m3)Most of the specific gravity of soil fall within a range of 2.6 – 2.9
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Relationships between Unit weight, Void ratio, Moisture Content and Specific
gravity
let us consider a volume of soil in which the volume of the soil solids is one
Derivation of equationsTherefore Gs will be substituted as
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Derivation –cont’d
γγ = W = WS +WW =GS γγ W + wGs γγ W = (1+w) Gs γγ w
V V 1+e 1+e
γγ d= Ws = Gs γγww
V 1+e
S= Vw = wGsVv e
Therefore
How Vw become wGS???
Vw = Ww = wGs γγ w =wGsγγ w γγ w
Derivation –cont’d
γγ sat = W = WS +WW = Gs γγ w + e γγ w = (Gs+e) γγ wV V 1+ e 1+e
So if S = 1 (100%)
Se = wGs
e = wGs
Beside bulk unit weight, dry unit weight and
saturated unit weight there is another type of
unit weight that is submerge unit weight, γγ’=
γγ sat- γγ w
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Relationships between Unit weight, Porosity, Moisture Content
and Specific gravity
Relationships between Unit weight, Porosity, Moisture Content
and Specific gravity
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Relationships between Unit weight, Porosity, Moisture Content
and Specific gravity (Saturated Case)
Relationships between Unit weight, Porosity, Moisture Content
and Specific gravity
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Air Content� The air content, A can be expressed as
� A = e- wGs / 1+ e
� or A = e/ 1+e ( 1- wGs/e)
� Since n = e/1+e
� Therefore, A = n (1-Sr)
� Beside using symbol A as air content sometimes authors use Na
Relative Density
� Dr= relative density (%)
� e = in situ void ratio of the soil
� emax = void ratio of the soil in the loosest state
� emin = void ratio of the soil in the densest state
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Relative Density
� Dr= relative density (%)
� ρd = in situ dry unit weight of the soil
� ρd(max) = void ratio of the soil in the loosest state
� ρd(min) = void ratio of the soil in the densest state
Relative Density