basis physical property

Topics: Density, Fundamental physics concepts, Relative density Pages: 15 (716 words) Published: November 3, 2014
01/03/2012

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
where
Vs =
volume of soil solids
Vv =
volume of voids
Vw =
volume of water in the
voids
Va =
volume of air in voids

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Relationship equations
W = Ws + Ww
where,
Ws =
Ww=
Wa =

( eq. 2)

weight of soil solid
weight of water
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 ) = n
Vs
V – Vv 1 – (Vv/V)
1- n

n=

e
1+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 equations
Therefore Gs will be substituted as

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Derivation –cont’d

γ = W = WS +WW =GS γ W + wGs γ W = (1+w) Gs γ w
V
V
1+e
1+e
γ d= Ws = Gs γw
V
1+e

Therefore

Vw = Ww = wGs γ w =wGs
γw
γw

How Vw become
wGS???

So if S = 1
(100%)

S= Vw = wGs
Vv
e

Se = wGs

Derivation –cont’d

e = wGs
γ sat = W = WS +WW = Gs γ w + e γ w = (Gs+e) γ w
V
V
1+ e
1+e

Beside bulk unit weight,
dry unit weight and
saturated unit weight
there is another type of
unit weight that is
submerge unit weight, γ’=
γ sat- γ 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

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Relative...
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