the determination of the size range ofparticles present in a soil, expressed aspercentage of the total dry weight.

In any soil mass, the sizes of the grainsvary greatly. To classify a soil properly,you must know its grain-sizedistribution.

Two Methods Use in Determining the Particle SizeDistribution of Soil

1. Sieve Analysis

Use in determining particle size distribution for coarse rained soil (For particle sizes larger than 0.075 mm in diameter)

2. Hydrometer Analysis

Use in obtaining the particle size distribution for fine rained soil (For particle sizes smaller than 0.075 mm in diameter)

A sieve analysis is conducted by taking a measuredamount of dry, well-pulverized soil and passing itthrough a stack of progressively finer sieves with a pan atthe bottom. The amount of soil retained on each sieve ismeasured, and the cumulative percentage of soil passingthrough each is determined. This percentage is generallyreferred to as percent finer.

1. Oven dry the soil and then break all lumps into smaller particles .

2. The soil is then shaken through a stack of sieves with openings of decreasingsize from top to bottom.

3. After the soil is shaken, the mass of soil retained on each sieve and pan isdetermined.

4. Determine the total mass of the soil : M1 + M2 + ….Mn =Ʃ M.

5. Determine the cumulative mass of soil retained above each sieve. For the ithsieve, it is : M1 + M2 + ….Mi

6. The mass of soil passing the ith sieve is ƩM – (: M1 + M2 + ….Mi)

7. The percent of soil passing the ith sieve( or percent finer) is

8 . Once the percent finer for each sieve is calculated, the calculations are plottedon semi logarithmic graph paper with percent finer as the ordinate and sieveopening size as abscissa which is referred to as the particle size distribution curve.

based on the principle of sedimentation of soil grainsin water. When the soil specimen is dispersed in water,the particles settle at different velocities, depending ontheir shape, size, and weight, and the viscosity of thewater. For simplicity the soil particles are assumed tobe sphere.

1. Effective Size (D10)

The diameter in the particle-size distribution curve corresponding to 10% finer.

Good measure to estimate the hydraulic conductivity and drainage through soil

2.Uniformity Coefficient (Cu)

3. Coefficient of Gradation( Cc)

Cc =[D30]2/[(D60)(D10)]

4. Sorting Coefficient( So)

1.Poorly Graded Soil

Particle sizes are distribute over a wide range

2.Well Graded Soil

Has uniformity coefficient greater than about 4 forgravel and 6 for sand and coefficient of gradationbetween 1 to 3( for gravel and sands)

3.Gap Graded Soil

Combination of two or more uniformly gradedfractions

Soil classification: “The ordering of soilsinto a hierarchy of classes. The product isan arrangement or system ofclassification designed to expressinterrelationships of soils and to serve asa filing system. Broad groupings are madeon the basis of general characteristics;subdivisions on the basis of more detaileddifferences in specific properties.” – SoilScience Society of South Africa

Why would we want to classify?To enable communication betweenspecialists

In theory constructionAdvancement in science = the ability to

make generalizations and predictivestatements

For mapping purposes

USDA CLASIFICATION SYSTEM

AASHTO SOIL CLASSIFICATION SYSTEM

USCS