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# GATE Q&A for Origin of soils and Clay Mineralogy

Question No 1

1. The clay mineral primarily governing the swelling  behavior of black cotton soil is  [GATE, 2014]  (A) halloysite  (B) illite  (C) kaolinite  (D) montmorillonite

Ans : Montomorillonite mineral exhibits the swelling behavior in black cotton soils.  Hence, the correct answer is option (D).

Question No 2

2. An earth embankment is to be constructed with compacted cohesionless soil. The volume of the embankment is 5000 m3 and the target dry unit weight is 16.2  kN/m3. Three nearby sites (see the given figure) have  been identified from where the required soil can be  transported to the construction site. The void ratios  (e) of different sites are shown in the figure. Answer  the specific gravity of soil to be 2.7 for all three sites.  If the cost of transportation per km is twice the cost  of excavation per m3 of borrow pits, which site would  you choose as the most economic solution? (Use unit  weight of water = 10 kN/m3) [GATE, 2015]
(A) Site X (B) Site Y  (C) Site Z (D) Any of the sites

Ans :

Question No 3

3. The relationship between porosity (η), specific yield  (S y) and specific retention (Sx) of an unconfined aquifer is [GATE, 2015]
(A) S y + Sx = η
(B) S y + η = Sx
(C) Sx + η = S y
(D) S y + Sx + η = 1

Ans :
Porosity = Specific yield + Specific retention  η = Sy + Sr
Hence, the correct answer is option (A).