Civil Engineering - Soil Mechanics and Foundation Engineering - Discussion

5. 

Which one of the following statements is true ?

[A]. Clays are more porous than sands
[B]. Pressure of organic matter in a soil decreases the bearing capacity of the soil
[C]. Aluminous cement is used for foundations in soils with chemical deposits
[D]. All the above.

Answer: Option D

Explanation:

No answer description available for this question.

Tine said: (Jan 7, 2014)  
How can clay be more porous as compared to sand?

Mayuri Patil said: (Feb 27, 2014)  
Porosity of clay is 33-60%.

And porosity of sand is 20-35%.

Hence clay is more porous than sand.

Chandan Ku said: (Mar 31, 2014)  
How many type of cement used in construction?

Biswa said: (May 8, 2014)  
Water easily pass through sand, but not incase of clay. So how option A is right?

Vk Kushvaha said: (Jun 29, 2014)  
Porosity is inversely proportional of permeability.

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

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

Bob Rat said: (Aug 13, 2014)  
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.

Yaregal said: (Feb 18, 2015)  
Pore size and it's connectivity determines the porosity of the soil. It is possible to have almost zero permeability for large spacing.

Akhil Ks said: (Feb 20, 2015)  
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.

Shehzad said: (Feb 28, 2015)  
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.

Abi said: (Feb 28, 2015)  
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.

Vicky said: (Nov 4, 2015)  
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.

Balram Yadav said: (Nov 17, 2015)  
Question is wrong. It need to be corrected, because clay will never be porous than sand.

Nitesh said: (Nov 29, 2015)  
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.

Shivam Chaudhary said: (Jan 11, 2016)  
The particle size range for sand as per IS soil classification?

Sravya said: (Mar 27, 2016)  
Yes, the clay has less porous than sand.

Divyesh Patel said: (Apr 10, 2016)  
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.

Shahin Vk said: (Apr 14, 2016)  
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.

Kiran said: (May 7, 2016)  
The porosity of clay is more than the sand.

Krishna said: (May 14, 2016)  
Clay is more porous than sand and sand has more permeability than clay.

Vikram said: (Jun 22, 2016)  
Clay is impermeable in nature.

Sand has high permeability.

Karan said: (Sep 4, 2016)  
This answer is wrong as sands are more porous clays.

Ayush said: (Nov 23, 2016)  
This can easily be understood by flour wheat example as after grinding of wheat it's volume increase as flour is finer its void ratio increases hence clay is porous than sand.

Chintu said: (Feb 18, 2017)  
Guys porosity is the water bearing capacity.

Clay can hold more water than sand.

Engir said: (Apr 8, 2017)  
Clays: Porous but impermeable (i. E they store water but not yield them back, because of tight molecular structure) as Aquicludes.

While Sand: yield sufficiently and are highly permeable (because of large grain size) but not as porous than clay.

Indhu said: (Apr 29, 2017)  
As the size of the particle decreases, porosity will increases. Hence on comparing the clay and sand particle, clay is having greater porosity. Even though the porosity of clay is higher, it doesn't mean that its permeability is more than sand. Since only interconnected pores will allow the passage of fluid.

Bunu said: (May 6, 2017)  
Aluminous cement is used for what type of chemical deposit?

Bhaskar Manna said: (May 17, 2017)  
I think Option B is the correct answer.

Hatem Alhamaidi said: (Aug 21, 2017)  
Clay is more porous than sand. The Permeability of sand is higher.

The reason for that is clay particles are platy and smaller in size which allows it to have more void space as a total, however, the individual spaces are smaller in size than the void spaces created by the sand particles. Other factors affecting the analysis is the tendency of clay to swell which allows it to have even higher volume than the sand. The Degree of compaction and initial void ratio and initial moisture content are other factors. In controlled testing where equal volumes of clay and sand (clay is suppressed with surcharge weights to avoid swelling), the porosity of clay would be higher than that of sand. The permeability of sand is obviously higher than clay which is not debatable.

Wangudu said: (Oct 31, 2017)  
@Chintu is right. Porosity is water holding capacity. So clay is more porous than sand.

Ganesh Vg said: (Dec 1, 2017)  
I think porosity is the number of pores. Not the holding capacity.

Ayon said: (Jan 6, 2018)  
Yes, porosity (No of the pore) is more in clay but it's not continuous.

Om Prakash said: (Feb 15, 2018)  
Porosity and permeability are directly proportional and its fact that porocity of clay is more then that of sand but in case of clay, particle are electrically charged and due to charged partical waters are hold by clay.

Viki said: (Feb 24, 2018)  
1. The main advantage is that it can withstand high temperatures so that it can be used in refractories, foundries and other workshops where high temperatures are involved.

2. The initial setting time is 3 hours than compared to that of PPC cement. And the final setting time of cement is 5 hours.

3. High Alumina Cement evolves great heat when setting so that these cements can be used in colder temperatures.

4. It is highly resistants to even concentrated acids and thereby it is widely used in chemical industries.

5. It sets fast and it attains a strength of 40 N/mm2 in just one day and 50 N/mm2 in three days.

Mohot Singh said: (Mar 15, 2018)  
We know that clay is less permeable then sand. And permeability is directly proportional to porosity then how clay is more porose then sand.

Dilip said: (Aug 18, 2018)  
Can anyone explain option C?

Niazi said: (Nov 6, 2018)  
Clay have more surface area than sand, thats why clay have more porosity than sand. As a thin water film is just on particles of clay and have less voids, permeability of clay is less than sand.

Tapas said: (Nov 9, 2018)  
Porosity has nothing to do with the passage of water through the soil much, it is the measure of pores present. In other words, it is the measure of how much water can the soil mass retain. As clay particles are the smallest so their intermolecular voids sum up to me much greater than that of sand. So, the pores present in clay mass is highest so is its water retaining capacity and so is its porosity.

Kiran said: (Jan 7, 2019)  
Presence of organic matter in the soil.

Not pressure of organic matter.

Manoj said: (Feb 6, 2019)  
What is the relation between Porosity, permeability and capillary rise ?

Abinet said: (Apr 13, 2019)  
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.

Jatin said: (Apr 29, 2019)  
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.

Sarada Panda said: (Aug 8, 2019)  
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.

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