Civil Engineering - Soil Mechanics and Foundation Engineering - Discussion

I agree with you @Biswa because it is totally wrong clay has less porosity than sand.

We know that clay is less permeable then sand. And permeability is directly proportional to porosity then how clay is more porose then sand.

Porosity: is a measure of the void spaces in a material.

Permeability: a measure of the ability of a material (such as rocks) to transmit fluids.

Porosity and permeability are related properties of any rock or lose sediment. Both are related to the number, size, and connections of openings in the rock. More specifically,
the porosity of a rock is a measure of its ability to hold a fluid. Mathematically, it is the open space in a rock divided by the total rock volume (solid and space). Permeability is a
measure of the ease of flow of a fluid through a porous solid. A rock may be extremely porous, but if the pores are not connected, it will have no permeability. Likewise, a rock may have a few continuous cracks which allow ease of fluid flow, but when porosity is calculated, the rock doesn't seem very porous.


Louisiana subsurface sediments consist mostly of gravel, sand and clay. Clay is the most porous sediment but is the least permeable. Clay usually acts as an aquitard, impeding the flow of water. Gravel and sand are both porous and permeable, making them good aquifer materials. Gravel has the highest permeability.

Regarding porosity:

Number of pores in fine-grain soil>>> Number of pores in CGS. Therefore porosity is high.

Imagine the number of FGS particles present in 1kg soil v/s number of cgs particles present in 1kg soil. Fgs outnumber the cgs zillion times.

Option A is wrong I think.

According to me, the correct answer is "Clay is more porous than the sand".

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.

At what % of shear strain the interlocking resistance in loose sand break? Please give details.

Porosity is inversely proportional of permeability.

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

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