DETERMINATION OF THE GRAIN SIZE DISTRIBUTION BY SIEVING

TITLE:

DETERMINATION OF THE GRAIN SIZE DISTRIBUTION BY SIEVING

OBJECTIVES:

• To determine the distribution of coarse grained soil.

•  To classify the coarse grained soils.

THEORY:

 Soil having particle larger than 0.075 mm size are termed as coarse grained soils. In these soils, more than 50% of the total material by mass is larger than 75 Micron. Coarse grained soil may be a boulder, cobble, gravel and sand.

Boulder- more than 300 mm diameter.

Cobble-  smaller than 300 mm and larger than 80 mm diameter.

Gravel- smaller than 80 mm and larger than 4.75 mm diameter.

    Coarse grained - 80 mm to 20 mm.

    Fine gravel- 20 mm to 4.75 mm.

Sand- smaller than 4.75 mm and larger than 0.075 mm diameter.

   Coarse- 4.75mm to 2 mm

   Medium:2.0 mm to 4.25 Micron

TITLE:

DETERMINATION OF THE GRAIN SIZE DISTRIBUTION BY SIEVING

OBJECTIVES:

• To determine the distribution of coarse grained soil.

•  To classify the coarse grained soils.

THEORY:

 Soil having particle larger than 0.075 mm size are termed as coarse grained soils. In these soils, more than 50% of the total material by mass is larger than 75 Micron. Coarse grained soil may be a boulder, cobble, gravel and sand.

Boulder- more than 300 mm diameter.

Cobble-  smaller than 300 mm and larger than 80 mm diameter.

Gravel- smaller than 80 mm and larger than 4.75 mm diameter.

    Coarse grained - 80 mm to 20 mm.

    Fine gravel- 20 mm to 4.75 mm.

Sand- smaller than 4.75 mm and larger than 0.075 mm diameter.

   Coarse- 4.75mm to 2 mm

   Medium:2.0 mm to 4.25 Micron

   Fine: 425 Micron to 75 Micron. 

Soil having less than 5% of particles of size smaller than 0.075 mm are designed by the symbols

GW- well graded gravel

GP- poorly graded gravel

SW-well graded sand

SP- poorly graded sand

Dry sieve analysis is done if fines are less than 5% for cohesionless soil.

Wet sieve analysis is done if fines are more than 5% and cohesive in nature.

 The degree of uniformity of soil is expressed by the coefficient of uniformity, which is,

`C_u=D_(60)/D_(10)`

 To identify whether the soil is uniform or well graded, coefficient of curvature is used, which is,

`C_c=D_(30)^2/(D_(10)*D_(60))` 

PROCEDURES:

Sieve analysis is carried out by using a set of standard sieve. A known quantity of air dried soil was taken.The soil was then passed through a set of sieves. The sieves are arranged in such a way that the sieve with the largest opening is at the top and the sieve with smaller opening is at the bottom. The set of sieve was then taken for 10 minutes in the sieve shaker. The soil retained on each sieve was computed. Then, the percentage retained on each sieve was computed. Finally, the percentage of particles finer than sieve size was then used in the analysis. 

OBSERVATIONS:

CALCULATIONS:

Now, from the semi log graph, we get

Note:These data may slightly vary as per person ...

`D_(10)=0.2`

`D_(30)=0.49`

`D_(60)=1.5`

The coefficient of curvature is,

`C_c=D_(30)^2/(D_(10)*D_(60))` 

`=0.8`

The coefficient of uniformity is,

`C_u=D_(60)/D_(10)`

`=7.5`

RESULTS:

Thus, the coefficient of curvature and uniformity are found to be `0.8` and  `7.5`, which shows that the given soil is medium graded (as given by uniformity coefficient) and slightly poorly graded (as given by value of `C_c` since it doesn't lies between 1 and 3).

PRECAUTIONS:

1. While drying, the temperature of the oven should not be more than 105 degree Celsius because higher temperature may cause some permanent change in the 75 Micron materials.

2. During shaking, soil sample should not be allowed to come out.

CONCLUSIONS:

Hence, the grain size distribution was determined by sieve analysis.