Wet Analysis, Important co-efficient, Relative Density

1. Wet Analysis:
   This method of analysis is used for the particles of size less than 75mic, because they can not be analysed using the mechanical sieve analysis. Wet analysis of the soil is based upon the Stoke's law. The sample which passes through the IS Sieve of diameter 75 micron is taken and is mixed in the water to settle down. It is assumed that the particles settle down, in different layers of different sizes.There are few assumptions made in the wet analysis of the soil particles:
   (a) The particles are spherical in shape.
   (b) The particles are of smaller sizes and are not affected by the other particles while the settlement takes place.
   (c) It is required that the liquid through which the particles pass must be of indefinite extent.
2. Important co-efficient:

1. Co-efficient of uniformity: The co-efficient which describes the uniformity of the soil is known as the uniformity co-efficient. It is represented as Cu and can be obtained by the following formula:

Cu= D60/D10

Where D60 is the diameter of the Sieve through which the 60% of the soil sample passes down.

D10 is the diameter of the IS Sieve through which only 10% of the soil sample passes down. Larger the value of the Cu, larger is the range of the particle sizes, and if it is lower that means the particles are of almost the same diameter.

If the value of the Cu is smaller than 2, then it is considered as the uniformly graded soil, containing particles of almost same size. For well graded gravel, Cu>= 4

and for well graded sand, Cu>=6.

2. Co-efficient of Curvature: The co-efficient of curvature describes the general shape of the particle distribution curve. It is denoted by Cc.

It can be calculated as below:

Cc= (D30)²/ D60*D10

For well graded soil the co-efficient of curvature lies between 1 and 3.

3. Relative Density:

Relative density is an important index property of the cohesionless soil, it is also termed as the relative compactness of the natural soil deposits of the cohesionless soil. It is represented by I_D

and can be calculated as (e_max- e)/(e_max – e_min).

'e' is the natural void ratio and other two are maximum and minimum of the given soil sample. The value of the relative density is 0 when the soil is present in its loosest state in nature, and it is equal to 1 when it is present in its densest state in nature.

S.No.	Value of relative density	Type of soil
1	0 to 0.15	Very loose
2	Between 0.15 to 0.35	loose
3	Between 0.35 to 0.65	Medium dense
4	Between 0.5 to 0.85	Dense
5	0.85 to 1	Very dense.