Civil Engineering - Soil Mechanics and Foundation Engineering - Discussion

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.

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

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.

Porosity is inversely proportional of permeability.

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

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

Water easily pass through sand, but not incase of clay. So how option A is right?

How many type of cement used in construction?

Porosity of clay is 33-60%.

And porosity of sand is 20-35%.

Hence clay is more porous than sand.

How can clay be more porous as compared to sand?