Soil Permeability
Permeability is the Ease with which the water can flow through the soil. It helps us to understand engineering problems like seepage problems, settlement calculations etc.
What is permeability?
Permeability is the Ease with which the water can flow through the soil. Larger the pores more the permeability and vice versa.
• Gravel would have the more permeability compare to the sand, silt and clay.
• Flocculated structure would have more permeability than the dispersed structure
Why should we measure permeability?
• It helps us to understand engineering problems like seepage problems,settlement calculations etc.
• Pore water pressure existed will develop the stress and it will dissipate with time based on the permeability and finally the settlement takes place.
Darcy's Law
Q=KiA.
• V = Superficial velocity
• i = Hydraulic Gradient
• K = Coefficient of permeability.
Flow is assumed as laminar, valid for all the soils except for coarse gravel. Superficial velocity V is calculated considering the flow through the entire area.
What are the methods for determination of permeability?
Laboratory tests.
• Constant head permeability test.
• Variable head permeability test.
Field tests.
• Pumping out tests.
• Pumping in test.
Indirect methods.
• If the particle size and specific surface area are known then permeability can be determined.
• From the consolidation data
What are the factors affecting permeability?
• Particle size
• Effect of void ratio
• Effect of permeant
• Shape of particles
• Degree of saturation
• Effect of soil fabric
• Impurities in water
• Effects of adsorbed cation on clay mineral surface