Civil Engineering - Soil Mechanics and Foundation Engineering - Discussion

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.

Clay particles are small in size, and pore water pressure is large, on the other hand for sand pore space is large but small in number for the same volume as clay and poor water pressure low. That's why the quick range of gravitational water (permeability).

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

Porosity = Volume of void/Total volume(Vv/V).
Since the Volume of void (Vv) is more in clay than sand.
Hence, Clay is more porous than sand.
So option D is correct.

Simply;

Porosity = Volume of the Void/Total volume of the soil mass, It indicates that the quantity of void in soil contain in which the void remains in the soil. The void are contained more than the sand. So D is the correct answer.

Option A is not in Answer n = Vv/V α K.

The material which is more porous will allow the liquid to pass though it easily. Statement was not about porosity, its about porous. Hence sand is more porous than clay.

Material with good porosity can be called "porous".

Mathematically, porosity can be expressed as the ratio of the volume of pore space to the total volume of the material.

Porosity :

Well-sorted sand or gravel 25-50%.
Silt 35-50%.
Clay 33-60%.

Permeability:
Well-sorted sand or gravel High.
Silt Medium.
Clay Low.

Clay soils are more porous than sandy soils. True because porosity is the ability of a material to hold water where as permeabilty is the ability of a material to allow passage of water through it.

What is the relation between Porosity, permeability and capillary rise ?