Civil Engineering - Soil Mechanics and Foundation Engineering - Discussion

Question is wrong. It need to be corrected, because clay will never be porous than sand.

Porosity is measure that tells you how much water can be retained in a soil while permeability is measure of ease with which water can pass through. So clay is more porous.

The particle size range for sand as per IS soil classification?

Yes, the clay has less porous than sand.

Porosity of clay is 33-60%.

And porosity of sand is 20-35%.

Hence clay is more porous than sand.

Porosity is inversely proportional of permeability.

That is porosity of clay >silt >sand > gravel.

Where as permeability is gravel >sand >silt> clay.

Porosity and permeability are directly proportional. As your porosity increases, so does your permeability. Porosity is related mathematically to your void space as porosity, let's call it p, p = v_v/v_t where v_v is volume of voids and v_t is volume total.

If your void space is increased then the ability for water to flow through is also increased because there is more space for fluid to flow naturally. Therefore, Biswas's confusion above is legitimate. This question is improperly worded.

Pore size and it's connectivity determines the porosity of the soil. It is possible to have almost zero permeability for large spacing.


Porosity refers to the open spaces within a material. Porosity values are based on the ratio of pore volume to total volume and it is more in clayey soil.

Porosity of gravel: 25-40%.

Porosity of sand: 25-50%.

Porosity of clay: 40-70%.

Permeability refers to the ability of a material to allow for the passage of a fluid due to interconnected voids. Permeability of gravel>sand>clay.

Yes, porosity (No of the pore) is more in clay but it's not continuous.

The porosity of clay is more than the sand.

Clay is more porous than sand and sand has more permeability than clay.

Clay is impermeable in nature.

Sand has high permeability.

This answer is wrong as sands are more porous clays.