Cation exchange capacity is factor influencing swelling of soil. The degree of shrinkage depends upon type and amount of clay minerals, mode and environment of deposition.

As per IS: 2720-part 40, free swell of a soil is defined as increase in volume of a soil without any constrains, on submergence in water.

Adsorbed water which is attracted by forces within soil and pore water are two types of soil water divided based on inter-particle forces.

As neutral pressure should not have any effect on void ratio or property of soil, it is transmitted through pore fluid.

The ratio of water adsorbed by dry soil in a saturated atmosphere at a given temperature to weight of oven-dried soil, has following average values Sands 1% silts 7%, clays 17 %.

Explanation:

Effective stress is ratio of force at contact of particles of soil to total area. It cannot be obtained practically but we can calculate effective stress by measuring total stress and pore water pressure as:

Total stress (σ) = effective stress (σ’) + pore water pressure (u)

Effective stress (σ') = Total stress (σ) - pore water pressure (u)

If we increase ground water table n value of pore water pressure increases and effective stress decreases.

If we lowering groundwater table below ground n value of pore water pressure decreases and effective stress increases. 

Due to frost boils, re is a formation of pot holes by extrusion of soft soil and water under dynamic action of wheel loads.

Rise in temperature results in a decrease of surface tension (TC) and hence decrease in soil suction.

The maximum capillary rise is given by,
(h_c)_max=4T_s/(?_wd)
At 20°C, T_s=72.8 dynes/cm and ?_w=9.78kN/m³
? (h_c)_max=4*72.8 *10^-8/(9.78*10^-6* d)
? (h_c)_max=0.2975/d cm.

The effective stress principle was given by Terzaghi. It is physical interaction between water and soil solids.

This concept was assumed to be applied to fully saturated soil and relates 3 types of stresses. i.e. total stress, Pore water pressure and effective stress.

Mamatically, σ? = σ - U

• The effective stress diagram of soil for submerged and saturated soil is different because buoyancy effect is taken into account in case of submerged soil.
• In submerged soil, pore water pressure is equal to hydrostatic pressure, which means that effective stress is reduced due to upward force of water.
• Hence effective stress in zone of submerged soil will become 0