# Civil Engineering - Soil Mechanics and Foundation Engineering - Discussion

### Discussion :: Soil Mechanics and Foundation Engineering - Section 1 (Q.No.5)

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.

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.

 Ravi Ahir said: (Oct 22, 2019) Option A is not in Answer n = Vv/V α K.

 Dhan Bahadur K.C. said: (Apr 19, 2020) 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.

 Abhijeet Singh said: (Apr 22, 2020) 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.

 Pankaj said: (Jun 7, 2020) I agree with you @Biswa because it is totally wrong clay has less porosity than sand.

 Souryakanti Rana said: (Jun 16, 2020) 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).

 Murtaza said: (Aug 28, 2020) 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.

 Shianrilong Reamei said: (Sep 23, 2020) 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.

 Masum said: (Nov 4, 2020) Option A is wrong I think.

 Rajbanshi said: (Jun 12, 2021) According to me, the correct answer is "Clay is more porous than the sand".

 Ziyaurahman Ansari said: (Jun 23, 2021) 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.

 Naresh said: (Aug 29, 2021) Clay has a flocculated structure which increases its void but the flocculated structure does not allow percolation of water.

 Saroja said: (Sep 16, 2021) At what % of shear strain the interlocking resistance in loose sand break? Please give details.

 Vikas said: (Dec 11, 2021) 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.

 Smile said: (Jun 4, 2022) As The surface area increase, proportionally the porosity also increases as the clay has more surface area than sand it is more porous.