Civil Engineering - Soil Mechanics and Foundation Engineering - Discussion

The porosity of clay is more than the sand.

Sand is more porous than clay because sand particles are larger and the pore spaces between the particles are also larger. So a 'sand' can contain more fluid than a clay, which has platy particles that stack together well and limit the size and connectivity of the pore spaces.

But are you asking about porosity or about permeability?
Porosity is about the amount of physical 'room' in which fluids can be stored in a rock mass, and permeability is about how well the pore spaces are CONNECTED and therefore how well fluid can move through the rock.

A rock mass can be porous but not particularly permeable. So fluids may get into the rock but can't move around through it very well - such a rock is porous but not permeable.

A rock mass might be tight and not very porous but the pores or open spaces it does have might be large and connected (fractures, or even a cave system) and fluids can move 'through' that rock mass with great ease.

However, a sand is both more permeable and more porous than a clay.

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, the clay has less porous than sand.

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

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.

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

D correct.

Porosity - % age of availability of pores.

Permeability - % age of water flow through it.

In sand - Pores % age are less, so we are not compacted.

In soil - Pores % age are more, so we are compacted mechanical mean.

Simple.

Porous layer means D layer in which water can pass. As compared to clay the sand is more porous, so that in case of slow sand filter or rapid sand filter the sand bed are used.

Let us talk in terms of bulk density. Bulk density of clay's is less than that of sands. If we compare the masses of both clay and sand particles in two containers of equal volume, then there will be larger volume of voids inside the container of clay's which shows higher porosity of clay than sands.