Soil Mechanics (421-438)

Updated: Apr 28, 2020

a) Both A and R are true and R is the correct

explanation of A

b) Both A and R are true but R is not a correct

explanation of A

c) A is true but R is false

d) A isfalse but R is true


421. Assertion A : At depth Z below the surface of a submerged soil, water

pressure is γ𝓌 Z and it is the stress caused by the water which is called the "neutral stress".

Reason R : The water pressure acts equally in all directions and transmits the

same fully on grain to grain contact causing compression in the soil.

a

422. Assertion A : The safe height (2Z) to which an unsupported vertical cut in clay can be made is 4C/γ

Reason R : Active earth pressure of cohesive backfill shows that the negative

pressure (tension) is developed at top level. This tension decreases to zero at

depth Z and total net pressure up to a depth 2Z is zero a



423. Assertion A : Negative skin friction will act on piles in filled up soils, which should be considered in design of pile foundations.

Reason R : The filled up soils start consolidating and develop a drag force on

the pile a


424. Assertion A : Constant-head permeability test is not used for fine-grained soils.

Reason R :The lesser the permeability of the soil, lesser is the discharge

a

425. Assertion A : In box shear test, the failure plane is predetermined and is

horizontal.

Reason R : The shear stress is applied in the vertical direction

c

426. Assertion A : In the case of sand deposits with uniform density, N values are found to increase with depth.

Reason R : Overburden pressure increases with depth below ground level.

a

427. Assertion A : In the case of unconfmed compression test, Mohr's circle passes

through the origin.

Reason R : The major principal stress is zero.

c


428. Assertion A : Permeability continues to decrease with the increase in dry density of a compacted soil.

Reason R : Soil particles in water surroundings may be mutually attracted or

repulsed.

c

429. Assertion A : For a fully saturated soil, the pore pressure parameter is equal to

zero.

Reason R : The compressibility of water is much smaller than the coefficient

of volume compressibility.

d

430. Assertion A : Wash boring is recom mended to obtain undisturbed soil sample above ground water table.

Reason R : In wash boring, water pumped through the hollow drill rods

emerges through the ports of the chopping bit carrying disintegrated soil fragment. d

431. Assertion A : Terzaghi's theory of consolidation considers only primary

consolidation.

Reason R : Secondary consolidation takes place only at the end of the primary

consolidation. c

432. Assertion A : Mohr's circle for unconfmed compression test passes

through the origin.

Reason R : In an unconfmed compression test, the axial stress is equal to confining stress c



433. Assertion A : Secondary consolidation takes place at a rate much slower than that of primary consolidation..

Reason R : There is dissipation of excess pore water pressure during secondary consolidation. a

434. Assertion A : The ratio of operating frequency of machine 'f and natural

frequency of foundation soil system 4f should be either less than 0.5 or more than 1.5.

Reason R : The high amplitude caused during resonance (f = f) would damage

the delicate parts of the machine. a



435. Assertion A : When a saturated soil mass is subjected to consolidation, its volume at any instant is related to the total stress.

Reason R : Total stress is equal to the sum of the effective stress and pore water

pressure d

436. Assertion A : Highly plastic swelling type of clay can be best stabilized by

using lime as admixture.

Reason R : Absorption of water by lime in the soil improves its shear

resistance a

437. Assertion A : The load carrying capacity of bored cast in-situ pile in a sandy soil is much less than that of a driven pile of similar dimensions.

Reason R : A drive pile generates much more point bearing resistance than a

bored pile a

438. Assertion A : The phenomenon of quicksand occurs mostly in coarse sands

and gravels.

Reason R : Quicksand condition does not occur in clayey soils as their cohesion

holds the grains together even under upward flow at critical hydraulic gradient

d






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