Geotechnical · MCQ practice Shear Strength of Soils MCQs – Part 3
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Part 3 of 4 Question 31 Medium
Select the INCORRECT statement in the case of a triaxial test.
A The state of stress within the specimen during any stage of test as well as at failure is completely indeterminate B The stress distribution on the failure plane is uniform C All the three drainage conditions can be performed with complete control under the test D Precise measurement of pore pressure and volume change during test are possible
Answer: A. The state of stress within the specimen during any stage of test as well as at failure is completely indeterminate
In a triaxial test σ₁ and σ₃ are known at every stage, so the stress state is fully determinate. Statement (a) is incorrect.
Question 32 Easy
Which of the following parameters is determined by the triaxial test?
A Hydraulic gradient B Permeability C Shear strength parameters D Grain size
Answer: C. Shear strength parameters
The triaxial test gives the shear strength parameters c and φ (total or effective).
Question 33 Easy
Which one of the following tests cannot be done without undisturbed sampling?
A Shear strength of sand B Shear strength of clay C Compaction parameters D Atterberg limits
Answer: B. Shear strength of clay
Clay strength depends strongly on its natural structure and stress history, so an undisturbed sample is essential.
Question 34 Easy
The vane shear test is used to find the shear strength of:
A clayey soil B gravelly soil C sandy soil D all of the above
Answer: A. clayey soil
The vane test is suitable only for soft cohesive (clayey) soils.
Question 35 Medium
The appropriate triaxial test to assess the immediate stability of an unloading problem, such as excavation of a clay slope, would be the:
A Unconsolidated-undrained test B Consolidated-undrained test C Consolidated-drained test D Unconsolidated-drained test
Answer: A. Unconsolidated-undrained test
Immediately after excavation in clay there is no time for drainage, so undrained (UU) strength governs short-term stability.
Question 36 Easy
A footing is resting on fully saturated clayey strata. For checking the initial stability, shear parameters are used from:
A Consolidated undrained test B Unconsolidated drained test C Unconsolidated undrained test D Unconsolidated undrained test with pore pressure measurement
Answer: C. Unconsolidated undrained test
Initial (short-term) stability of a footing on saturated clay is governed by undrained strength: use the UU test.
Question 37 Easy
The effective stress strength parameters of a soil are c = 10 kPa and φ = 30°. The shear strength on a plane within the saturated soil mass at a point where the total normal stress is 300 kPa and the pore water pressure is 150 kPa will be:
A 90.5 kPa B 96.6 kPa C 101.5 kPa D 105.5 kPa
Answer: B. 96.6 kPa
\(\sigma' = 300 - 150 = 150\) kPa; \(\tau = 10 + 150\tan 30^\circ = 10 + 86.6 = 96.6\) kPa.
Question 38 Easy
The expansion of soil due to shear at a constant value of pressure is called:
A Apparent cohesion B True cohesion C Dilatancy D Consistency
Answer: C. Dilatancy
Volume increase during shearing (dense soils) is called dilatancy.
Question 39 Easy
The shear strength in plastic clay is due to:
A none of these B inter-granular friction C cohesion D internal friction
Answer: C. cohesion
Plastic clays get their strength mainly from cohesion.
Question 40 Medium
The shearing strength of a cohesionless soil depends on:
A Dry density B Rate of loading C Confining pressure D All the above
Answer: D. All the above
Sand strength τ = σ′ tan φ depends on confining (normal) pressure, on φ (which rises with dry density) and to a smaller extent on rate of loading.
Question 41 Easy
The strength of a soil is usually identified by:
A Direct tensile stress B Direct compressive stress C Ultimate shear stress D Effective stress
Answer: C. Ultimate shear stress
Soil strength is the ultimate (maximum) shear stress it can resist.
Question 42 Easy
The useful method of finding the shear strength of very plastic cohesive soils is by means of the:
A Cone test B Penetration test C Vane shear test D Torsional shear test
Answer: C. Vane shear test
Very plastic (soft) cohesive soils are best tested with the vane shear test.
Question 43 Easy
In a triaxial test:
A Stress in all the three directions is the same B Stress in all the three directions is different C Stress in vertical direction is different from the stress in the other two directions D Stress in X direction is equal to stress in Y and Z direction
Answer: C. Stress in vertical direction is different from the stress in the other two directions
The two horizontal stresses equal the cell pressure σ₃; the vertical stress σ₁ = σ₃ + σd is different.
Question 44 Easy
The process by which a mass of saturated soil, due to external forces, suddenly loses its shear strength and behaves as a fluid is called:
A Piping B Slide C Quick condition D Fluidity
Answer: C. Quick condition
Sudden loss of strength with fluid-like behaviour of saturated soil is the quick condition.
Question 45 Easy
The equation t = C + S tan φ (shear strength = cohesion + normal stress × tan φ) is given by:
A Rankine B Coulomb C Newton D Mohr
Answer: B. Coulomb
τ = c + σ tan φ is Coulomb's equation (1776).
Part 3 of 4