Introduction to soil

A short introduction about soil, three phase theory,main types of soil and their sizes

1. Soil Mechanics

CED, UET-P Muhammad Bilal



Three Phase theory
In geotechnical Engineering or soil mechanics the soil is considered to be made of three parts,
they’re air, water and soil solid. The air and water are collectively called voids



Classification of Soil


 In coarse grain soils we have gravel and sand
 In fine grain soils we have silt and clay

Coarse
grain
soil
Fine
grain
soil
Soil
Introduction to
Soil

2. Soil Mechanics

CED, UET-P Muhammad Bilal
Coarse grain soils
Type of soil Particle size range
Gravel Greater than 4.75mm
Sand Between 4.75-0.075mm
Fine grain soils
Type of soil Particle size range
Silt between 0.075-0.002mm
clay Less than 0.002mm

Besides that clay can be also called cohesive soil while the rest can be called non-
cohesive, cohesive means having low permeability which practically means it
won’t allow water to pass through it easily.
 Coarse grain soils has more bearing capacity than fine soils
 In lab if we want to check the distribution of different particles in coarse
grain soils we perform sieve analysis or mechanical analysis
ASTM D-6913
 For fine grain soils the test conducted is known as Hydrometer analysis
ASTM D-442
 Both these tests are conducted to obtain gradation curve
 Gradation curve is actually particle size in mm on x-axis and percent
passing on y-axis
 From gradation curve we can see the distribution of different particles in a
soil sample