Engineering Properties Of Soil

Phase diagram:-

                                  Generally, the soil is composed of 3 phase system is solid, liquid and gaseous matter. But in phase diagram only for understanding purpose, these three matters are shown separately.

3-Phase(partially saturated)

2-Phase(dry)

2-Phase(saturated)

Water content: 

It’s the ratio of the weight of water to the weight of the solids.

w = (W_w / Ws)*100 ,  w ≥ 0

where, W_w = weight of water

             Ws = weight of solids

Void ratio: 

It’s the ratio of the volume of voids to the volume of solids.

e =  V_v / V_s  ,  e > 0

 where, V_v =  volume of voids

 V_s =    volume of solids

 Porosity: 

It’s the ratio of the volume of voids to the total volume of soil.

n = (V_v / V)*100 ,  0 < n < 100

 where, V_v =  volume of voids

 V =    total volume of soil

 Degree of saturation: 

It’s the ratio of the volume of water to the volume of voids.

 S = (V_w / V_v)*100 ,  0 ≤  S ≤ 100

 where, V_w =  volume of  water

 V_v =     volume of voids

    for dry soil : S = 0

for fully saturated soil : S = 100

 Air content:

It’s the ratio of the volume of air to the volume of voids.

 a_c = V_a / V_v   = 1 - S

S + a_c = 1

where, V_a =  volume of  air

 V_v =     volume of voids

 % Air void:

It’s the ratio of the volume of air to the total volume of soil.

% n_a = (V_a / V)*100

     n_a = n.a_c

where, V_a =  volume of  air

 V = total volume of soil

Unit weight:

a)    Bulk unit weight

It’s the total weight per unit volume.

γ = W / V  = (W_S + W_w ) / (V_s + V_w + V_a)

b)    Dry unit weight

It’s the weight of soil solids per unit volume.

γ_d = W_s / V   

γ_d is used as a measure of the denseness of soil. Means more γ_d,  more compacted soil.

c)     Saturated unit weight

It is the ratio of total weight of fully saturated soil sample to its total volume.

γ_sat = W_sat / V   

d)    Submerged unit weight

It is the submerged weight of soil solids per unit volume.

γ’ = γ_sat - γ_w

where, γ_sat = unit weight of saturated soil

               γ_w = unit weight of water

e) unit weight of solids

 γ_s = W_s / V_s

  Note: γ_s ˃ γ_sat > γ >  γ_dry > γ’

Specific gravity:

It is the ratio of the weight of a given volume of solids to the weight of an equivalent volume of water.

G = W_s / V_s.γ_w      = γ_s / γ_w    

 for inorganic solids, G = 2.6 to 2.75

for organic solids, G = 1.2 to 1.4

Relative density / Density index / Degree of denseness:

It is the ratio of the weight of a given volume of solids to the weight of an equivalent volume of water.

 I_{D =}  (e_max – e / e_max – e_min)*100%

Where, e_max = void ratio in loosest

e_min = void ratio in densest state

e =   void ratio in natural state

 Note: It represents relative compactness of coarse grained soil.

Difference between Relative compaction and Relative density:

Relative compactness	Relative density
It indicates the degree of the denseness of cohesive and cohesiveness soil.   R = γd / γd max	It indicates the degree of the denseness of natural cohesiveness soil.

Shape parameters:

a)    Coefficient of uniformity, C_u = D₆₀ / D₁₀

 

b)    Coefficient of curvature, C_c = D²₃₀ / D₆₀ x D₁₀

 

Where, D₆₀ is that size below which 60% particles are finer than this size by weight.

 D₃₀ is that size below which 30% particles are finer than this size by weight.

 D₁₀ is that size below which 10% particles are finer than this size by weight, D₁₀ is also known as effective size.