The post Solid-Water-Air Relation and Index properties of soil and their determination for coarse and fine grained soil appeared first on OnlineEngineeringNotes.
]]>Soil mass consists of solid soil particles containing void space between them. Space between the soil particles is known as void and these void is filled with either air or water or both.
The diagrammatic representation of the different phases in a soil mass is called phase diagram.
When soil masses consist of air, water and solid particles it is known as three phase system.
When soil masses consist of water and solid particle it is known as two phase system for saturated soil.
When soil masses consist of air and solid particle it is known as two phase system for dry soil.
Let,
V = Total volume of soil
Vs = Volume of solid particle
Va = Volume of air
Vw = Volume of water
Vv = Volume of void
So, from the definition of
Total volume of soil is equal to the sum of volume of air, water and solid particle respectively.
i.e. V = Vw + Va + Vs
or, V = Vs + Vv [∴Vw + Va ]
Similarly,
For weight
Total weight (W) = Weight of solid (Ws) + Weight of water (Ww) + Weight of air (Wa)
i.e W = Ws + Wa + Ww
Also,
Weight of void (Wv) = Wa + Ww
or, Wv = Ww [∴ Weight of air is negligible, so Wa =0 ]
∴ Wv = Ww
Total weight of soil mass,
W = Ws + Ww
Similarly, in terms of mass
M = Ms + Mw
1. Void ratio (e) = Volume of void (Vv) / Volume of solid (Vs)
2. Porosity (n) = Volume of void (Vv) / Total volume (V)
3. Degree of saturation (S or Sr)
or, S = Volume of water (Vw) / Volume of void (Vv)
4. Air content (ac) = Volume of air (Va) / Volume of void (Vv)
5. Percentage of air void (na) = Volume of air (Va) / Total volume (V)
6. Water content or Moisture content (w) = Weight of water (Ww) / Weight of solid (Ws)
7. Unit weight (γ) = Weight (W) / Volume (V)
a. Bulk unit weight (γ) = W / V
or, γ = (Ws + Wv) / ( Vs + Vv)
b. Dry unit weight (γd) = Ws / V
c. Saturated unit weight (γsat) = Wsat / V
d. Submerged unit weight (γsub) = Wsub / V
or, γsub = γsat – γw
or, γI = γsat – γw
e. Unit weight of solid (γs) = Ws / Vs
8. Specific gravity (G) = (Ms / Mw)
or, G = (Ms / Mw) = (ρs / ρw) = (γs / γw)
At 4o C
ρw = 1000 kg/m3 = 1g/ml
γw = 9810 N/m3 = 9.81 KN/m3
a. Relationship between e,w,Sr and G
We know,
e = Vv / Vs
or, e = (Vv / Vw) * (Vw / Vs)
or, e = (Vv / Vw) * (Ww / γw) * (γs / Ws)
or, e = (Vv / Vw) * (Ww / Ws) * (γs / γw)
or, e = (Vv / Vw) * w * G [∴ w = (Ww / Ws), G = (γs / γw) ]
or, e = (1/Vw / Vv ) * G * w
or, e = (1 / Sr) * w * G
or, Sr * e = w * G
∴ Sr * e = w * G
b. Relationship between e and n
n = Vv / V = Vv / (Vv + Vs)
or, 1/n = (Vv + Vs) / Vv
or, 1/n = 1 + (Vs / Vv)
or, 1/n = 1 + 1/Vv /Vs [∴ e = Vv / Vs]
or, 1/n = 1 + 1/e
or, 1/n = (e+1)/e
or, n = e / (e+1)
or, n(e+1) = e
or, e = ne + n
or, e = n / (1-n)
∴ e = n / (1-n)
c. Relationship between unit weight (γ) in terms of terms of water content (w), void ratio (e), specific gravity (G) and γw.
We know,
γ = W / V = ( Ws + Wv) / ( Va + Vs + Vw)
or, γ = ( Ws + Ww) / ( Vv + Vs) [∴ Ww = Wv]
or, γ = (Ws / Vs) * {(1 + Ww / Ws) / (1 + Vv / Vs)}
or, γ = γs * (1 + w) / (1+ e) ————–(1)
[∴w = (Ww / Ws), e = Vv / Vs ]
Also,
G = γs / γw
or, γs = G γw
Now, From equation (1) become,
∴γ= G γw (1 + w) / (1+ e)
d. Relationship between γ, G, Sr, e and γw.
We know,
γ = W / V
or, γ = (Ws + Wv) / (Vs + Vv)
or, γ = (Ws / Vs) * { (1 + Wv / Ws) / ( 1 + Vv / Vs) }
or, γ = γs * (1 + w) / (1 + e)
or, γ = G γw * (1 + w) / (1 + e)
or, γ = γw * { (G + Gw) / (1+e) } ————–(1)
We know,
Sre = wG ————-(2)
From equation (1) and (2), we get
∴ γ = γw * { (G + Sre) / (1+e) }
Condition:
γ as γsat
∴ γsat = γw * { (G + e) / (1+e) }
γ as γd
∴ γd = (γw * G)/ (1+e)
e. Relation between dry unit weight (γd), Bulk unit weight (γ) and water content (w).
We have,
w = Ww / Ws
Adding one on both side
w + 1 = (Ww + Ws) / Ws
or, w + 1 = (Ww + Ws) / Ws
or, w + 1 = W / Ws
or, Ws = W / (w + 1) ———–(1)
Also,
γd = Ws / V ————(2)
From equation (1) and (2)
γd = W / (w + 1) * 1 / V
or, γd = W / V (1 + w)
or, γd = W / V * 1 / (1+w)
or, γd = γ* 1 / ( 1 + w) [∴γ = W / V]
∴ γd = γ/ (1 + w)
f. Relationship between submerged unit weight (γI), specific gravity of solid (G) and void ratio (e).
We have,
γsub or γI = γsat – γw
But,
γsat = {(G + e) γw} / (1+e)
Now,
γI = {(G + e) γw / (1+e)} – γw
or, γI = {(G+e) γw – γw(1+e)} / (1+e)
or, γI = γw(G-1) / (1+e)
∴ γI = γw(G-1) / (1+e)
g. Relationship between dry unit weight (γd), specific gravity of solid (G), water content (w) and percentage of air void (na).
We have,
V = Vs + Va + Vw
or,V = Va + (Ww / γw) + (Ws / γs)
[∴γ = Ww / Vw, Simillarly γs = Ws / Vs]
Dividing both side by V, we get
1 = (Va / V) + (Ww / Vγw) + (Ws / Vγs)
But,
w = Ww / Ws
or,Ww = w * Ws
Now,
1 = na + {(w * Ws) / ( V * γw) } + Ws / V * γs
[∴ na = Va / V]
or, 1 – na = (Ws / V) * {(w / γw) + (1 / γs)}
or, 1 – na = (Ws / γw * V) * (w + γw / γs)
or, 1 – na = (Ws / γw * V) * (w + 1 / G)
[∴ G = γw / γs]
or, 1 – na = (γd / γs) *(w + 1 / G)
[∴γd = Ws / V]
or, γd = {(1-na) G γw} / (1 + wG)
When na = 0 (Fully saturated)
∴ γd = G γw / (1 + wG)
The properties of soil which helps to know engineering behaviors of soil and also helps to determine the classification of soil accurately is called index properties of soil.
The list of index properties:
a. Oven drying method:
Process:
Calculation:
Weight of container = W1
Weight of container + Wet soil = W2
Weight of container + Dry soil = W3
Water content (w) = (Ww / Ws) * 100%
or, w = {(W2 – W1) / (W3 – W1)} * 100%
Process:
Calculation:
M1 = Mass of empty pycnometer
M2 = Mass of dry sample fill in pycnometer
M3 = Mass of wet sample ( saturated sample)
M4 = Mass of water in pycnometer
Ms= Mass of dry soil
Now,
M4 = M3 – Ms + Mw
or, M4 = M3 – Ms + Vs *ρw
or, M4 = M3 – Ms + Ms * (1 / G) ————(1)
[∴ G = ρs / ρw]
Also,
Ms = M2 – M1
Putting the value in equation (1).
M4 = M3 – M2+ M1 + (M2 – M1) / G
or, M4 – M3 + M2 – M1 = (M2 – M1) / G
or, G = {( M2 – M1) / (M4 – M3 + M2 – M1)}
or, G = ( M2 – M1) / (M4 + M2) – (M1 + M3)
∴ G = ( M2 – M1) / (M4 + M2) – (M1 + M3)
Process:
Calculation:
M1 = Mass of clean core cutter
M2 = Mass of cutter with soil
H = Height of cutter
d = Diameter
A = Area of cutter
Now,
Mass of soil (M) = M2 – M1
Volume of soil = A * H = (πd2/4)* H
Where,
H = 130 mm
d = 100 mm
Then,
Density (ρ ) = M/V
Process:
Calculation:
Weight of soil in the hole = W1
Weight of pouring cylinder + sand before pouring = W2
Weight of cylinder + sand after pouring = W3
Weight of sand filling conical funnel = W4
Weight of sand filling hole = W2 – W3 – W4
Unit weight of sand = γ
Now,
Volume of sand = (W2 – W3 – W4) / γ
= Volume of hole = V
Bulk density (γ) = W1 / (1 + w)
Dry density (γd) = γ / (1+w)
Sedimentation analysis or wet mechanical analysis is conducted on soul fraction finer than 75micron which is kept in suspension in a liquid medium usually water.
Sedimentation analysis is based in Stoke’s Law according to which gives the terminal velocity of small sphere setting in a fluid of infinite extent.
Now,
Terminal velocity (v) = {gD2 * (G – 1) ρw} / 18η ———(1)
If a particle fall through height He in “t” minutes,
v = He / 60t ————-(2)
Combining equation (1) and (2)
D = M (He / t)1/2
Where,
M = {30η / g(G – 1) ρw }
a. Liquid limit (LL):
At liquid limit, the soil possesses a small value of shear strength. The liquid limit is the minimum water content at which the soil is still in liquid state but has a small shearing strengh agaist flowing.
b. Plastic Limit (PL):
In plastic limit soil can be moulded into any shape.
wp = Ww / Ws = (W1 – W2) / W2
where,
W1 = Weight of soil before drying
W2 = Weight of soil after drying
c. Shrinkage limit:
In shrinkage limit water content is lowest.
ws = {(M1 – Md) – (V1 – γd) γw} / Md
Where,
M1 = Mass of wet soil pat
V1 = Volume of wet soil pat
Md = Mass of fry soil pat
Vd = Volume of dry soil pat
Or,
ws = {(Vd γw) / Md} – 1/G
The post Solid-Water-Air Relation and Index properties of soil and their determination for coarse and fine grained soil appeared first on OnlineEngineeringNotes.
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