To determine the particle size distribution of coarse-grained soil by sieve analysis.

Object: To determine the particle size distribution of coarse-grained soil by sieve analysis.

Standard:

AASHTO:T88-86

ASTM:D422-82

BS1377:part 4

Apparatus:

• Stack of sieves, including pan and cover
• Balance (with an accuracy of 0.01 g)
• Rubber pestle and Mortar (for crushing the soil if lumped or conglomerated)
• Mechanical sieve shaker
• Oven

Theory:

The determination of the particle size distribution of soil is an important part of classification. The particle size distribution of granular soils is essential to the stability of the material for use in different civil works. Particle size distribution can be done by dry sieving or wet sieving. Dry sieving is done for coarse-grained soils, whereas wet sieving is performed for finer soils.

Procedure:

1. Take a representative oven-dried sample of soil.
2. If soil particles are lumped or conglomerated, crush the lumped and not the particles using the pestle and mortar.
3. Determine the mass of the sample accurately. W_t (g).
4. 
   
   Prepare a stack of sieves. Sieves having larger opening sizes (i.e., lower numbers) are placed above the ones having smaller opening sizes (i.e., higher numbers). The very last sieve is #200, and a pan is placed under it to collect the portion of soil passing the #200 sieve. Here is a full set of sieves. #4 and #200 should always be included
   
5. Make sure sieves are clean; if many soil particles are stuck in the openings, try to poke them out using a brush.
6. Weigh all sieves and the pan separately.
7. Pour the soil from Step 3 into the stack of sieves from the top and place the cover. Put the stack in the sieve shaker and fix the clamps; adjust the time to 10 to 15 minutes; and get the shaker going.
8. Stop the sieve shaker and measure the mass of each sieve + retained soil.

Calculations:

The results of the sieve analysis shall be reported as follows:

Weight of the dry soil sample =gm.

The percentage passing shall be plotted on the semi-logarithmic paper to obtain a curve known as the gradation curve.

Gradation curves are the best representation of soil nature, i.e., whether it is well-graded, uniformly graded, or poorly graded soil.

The uniformity coefficient (Cu) and coefficient of curvature (Cc) can also give us an idea of soil nature. They are calculated as follows:

(𝐷30)²

𝐶𝑐 = (𝐷60) ∗ (𝐷10) ==

𝐶𝑢 =

𝐷60

==

𝐷10

Where 𝐷10, 𝐷30 𝑜𝑟 𝐷60 are diameters or sizes for 10%, 30%, and 60% passing, respectively. Now,

If Cu > 5, the soil is well-graded.

If Cu< (5), the soil is uniformly graded.

And if Cc lies between 0.5 & 2, the soil is well graded.

Comments: