Civil Engineering - Soil Mechanics and Foundation Engineering - Discussion

Discussion Forum : Soil Mechanics and Foundation Engineering - Section 1 (Q.No. 5)
Which one of the following statements is true ?
Clays are more porous than sands
Pressure of organic matter in a soil decreases the bearing capacity of the soil
Aluminous cement is used for foundations in soils with chemical deposits
All the above.
Answer: Option
No answer description is available. Let's discuss.
57 comments Page 1 of 6.

Santosh Kumar said:   2 years ago
Of course, Clay is more porous but quite less permeable than sand.

Smile said:   2 years ago
As The surface area increase, proportionally the porosity also increases as the clay has more surface area than sand it is more porous.

Vikas said:   2 years ago
Porosity is a measure of pore spaces in soil. It is a volumetric ratio. It is ratio of total volume of voids (filled with water or air) to the total aggregate volume of soil mass.

It is dependent on so many factors like texture, structure, arrangements of particles and organic content.

Clays have particles size below 2 microns and these small particles have small pores and the interconnected pores gives more voids which makes it more porous.

Sand have particles size greater than clay and these particles have small pores compared to same volume.

Hence clays is highly porous than sand. However, clays are not permeable (water can't flow easily through them because of these small pore size) and sands on the other hand offer excellent drainage properties.

When it comes to porosity, then clay is more porous than sand. This is because the grain size of clay is much smaller than sand. So inter-granular space between the individual grains is much more in case of clay than sand. But all these pores are not interconnected so the permiability of clay is poor. However the intergranular space in sand is more so it has greater perbiability.

But then again everything can happen depending on the degree of compaction and lithification.

Porosity (n) is the percentage of void (Vv) in the total volume+void (V) of a solid of earth material. According to Fetter, pg 75, in table 3. 4, Porosity ranges for sediments.

Well-sorted sand or gravel = 25-50%.

Mixed sand and gravel = 20-35%.

Clay = 33-60%.

This is according to Meinzer (1923a) ; Davis, 1969; Cohen, 1965; and MacCary and Lambert, 1962.

So, Clay should be much porous than sand thou not pretty much.

As mentioned 'the dispersive effect of the electrostatic charge present on the surface of certain book-shaped clay minerals causes clay particles to be repelled by each other resulting in relatively large proportion of void space.

Saroja said:   3 years ago
At what % of shear strain the interlocking resistance in loose sand break? Please give details.

Naresh said:   3 years ago
Clay has a flocculated structure which increases its void but the flocculated structure does not allow percolation of water.

Ziyaurahman Ansari said:   3 years ago
A) Generally in the construction field, only 3 types of cement are mostly in practice

1. Ordinary portland cement,
2. Pozollona portland cement,
3. White cement.

Rajbanshi said:   3 years ago
According to me, the correct answer is "Clay is more porous than the sand".

Masum said:   4 years ago
Option A is wrong I think.

Shianrilong Reamei said:   4 years ago
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.

Murtaza said:   4 years ago
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.

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