Some important relations in between properties of soil

1.    Relation between W_s , W_w and w

                                                    from phase diagram,

total weight W = W_s + W_w + W_a

                                             = W_s + W_w + 0     (∵ W_a = 0)

                                = W_s{1+ (W_w/ W_s)}

                                                 W = W_s(1 + w)        (∵ w = W_w/ W_s ) 

           W_s = W / (1+w)

where, W_s = weight of solids

W_w = weight of water

W_a = weight of air

w = water content

1.    Relation between e and n 

we know that,

Porosity, n = V_v / V

 

n = V_v / (V_s + V_v)

 

n = (V_v/ V_s) / { 1+(V_v/ V_s)}

 

           n = e / (1+e)               (∴e = V_v/ V_s)

  Relation  between  e, S, w and G 

we know that,

Void ratio, e = V_v/ V_s

 

e = (V_v/ V_s) * (V_w/ V_w)

 

e = (V_v/ V_w) * (V_w/ V_s)

 

e =  (V_v/ V_w)*{(W_w /  γ_w ) / (W_s /  γ_s )}     (∴ γ_w = W_w/V_w)

 (∴γ_s = W_s/V_w)

e = (V_v/ V_w)* (W_w/ W_s)*(G_s. γ_w/ γ_w)    (∴ G_s = γ_s/ γ_w)

 

e = w G_s / S

 

Se = wG

 

 

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.

Classification of soil in civil engineering

 IS classification of soil:-

                                       it is classified into two categories.

• Coarse-grained soil:- (50% or more particles retained  on 75-micron sieve                         on the basis of % fineness coarse-grained soil can be further classified as:

1.  Gravel:-   50% or more than  retained on 4.75 mm sieve

case 1 :-   when fineness < 5% by weight 

           i) GW = well graded gravel

                                                  C_u > 4,  1<C_c<3

      ii) GP =  poorly graded gravel (in this values of C_u and C_c  are not satisfied)

                               

case 2 :- fineness in between 5% - 12%

     ( in this dual symbols are used. first for gradation and second for nature of fines. )

    

  i) GW - GC = well graded gravel containing clay 

 C_u > 4,  1<C_c<3

clay fraction > silt fraction

 ii) GP - GC  =  poorly graded gravel containing clay (in this values of C_u and C_c  are not satisfied)

clay fraction > silt fraction

iii) GW - GM = well graded gravel containing silt

 C_u > 4,  1<C_c<3

silt fraction > clay fraction

iv) GP - GM =  poorly graded gravel containing silt (in this values of C_u and C_c  are not satisfied)

silt fraction > clay fraction

case 3 :-   when fineness  > 12%  

 In this case, the soil is classified according to the I.S. plasticity chart (% I_p).

     i) GC = clayey gravel (I_p>7%)

clay fraction > silt fraction (because of % of I_p)

    ii) GM =  silty gravel (I_p<4%)

silt fraction > clay fraction (because of % of I_p)

2.  Sand:-   50% or more than  passed through 4.75 mm sieve

case 1 :-   when fineness < 5% by weight 

       i)  SW = well graded sand

 C_u > 6,  1< C_c<3

     ii) SP  =  poorly graded sand (in these values of C_u and C_c  are not satisfied)

case 2 :- fineness in between 5% - 12%

  i) SW -SC = well graded sand containing clay 

 C_u > 6,  1<C_c<3

clay fraction > silt fraction

  ii)  SP - SC  =  poorly  sand containing clay (in these values of C_u and C_c  are not satisfied)

clay fraction > silt fraction

 iii)  SW - SM = well graded sand containing silt

                 C_u > 6,  1<C_c<3

silt fraction > clay fraction

iv)  SP - SM =  poorly graded sand containing silt (in these values of C_u and C_c  are not satisfied)

silt fraction > clay fraction

case 3 :-  when fineness  > 12% 

in this case, the soil is classified according to the I.S. plasticity chart (% I_p).

    i)  SC = clayey sand (I_p>7%)

clay fraction > silt fraction  (because of % of I_p)

   ii) SM = silty sand (I_p<4%)

silt fraction > clay fraction (because of % of I_p)

Note:-  C_u  and  Cc are coefficient of uniformity and coefficient of curvature respectively. 

 % fineness means % fraction which pass through 75 micron sieve.

• Fine grained soil:-(50% or more particles  passed through 75 micron sieve)

1. silt (0.002 mm to 0.075 mm)
2. clay (size < 0.002 mm) :- it is classified as per % of liquid limit(LL)

  i) Low plastic soils (LL<35%)

CL= low plastic inorganic clay
ML= low plastic silt
OL= low plastic organic clay

ii) Medium plastic soils (35%<LL<50%)

CI= medium plastic inorganic clay

ML= medium plastic silt

OL= medium plastic organic clay 

iii) High plastic soils (LL>50%)

CL= high plastic inorganic clay
ML= high plastic silt
OL= high plastic organic clay

some clay minerals and their properties:-                                        

 

	CLAY MINERAL	BOND	EXAMPLE
1	Kaolinite mineral	Hydrogen bond	China clay
2	Illite mineral	Ionic bond
3	Montmorillonite	Water bond (weakest bond)	Black soil and Bentonite soil

  

What is soil and type of SOIL .?

What is soil?  

     Soil is a mixture of mineral particles, organic materials, air, water, and living organisms.

TYPE OF SOIL:-                                                                                                                         There are mainly 3 types of soil.

1. sandy soil:-  (size vary from 0.075 mm to 2 mm)

 It consists of small particles of breaking down of rocks like granite, limestone, and quartz. This is the poorest type of soil for the growth of plants, having low nutrients, acidic and poor water holding capacity. This type of soil good in the drainage system. In this soil Helical piers are used for the construction of buildings.

      

 

 2. Silt soil:-     (size vary from 0.002 mm to 0.075 mm)

soil that has particles smaller than sandy soil and larger than clay is known as silt soil. it's found near the river, lake and other water bodies.it is more fertile than the other type of soil.
This soil is not good for construction purposes.

3. Clay soil:-  (size less than 0.002 mm) 

It has the smallest particles among the others. particles are very close to each other and having good water holding capacity. it feels sticky when wet and smooth when dried.it is also called expensive soil. this causes foundations to crack, shift, and heave.

some different type of soil in India

1.lacustrine soil:-  deposited at the bottom of lakes

2.Alluvial soil:- transportation by running water

3.Aeoline soil:- transportation by wind 

4.Marine soil:- deposited in sea water

5.Peat/Muck soil:- organic soil