Test 11 - Shear Strength of Soils

Question 1 ప్రశ్న 1

Which equation correctly represents the Mohr-Coulomb shear failure criterion in terms of effective normal stress for a saturated soil?

A tau_f = c' + (sigma_n + u) tan(phi'), where u is pore-water pressure. B tau_f = c' + (sigma_n - u) tan(phi'), where sigma_n is total normal stress. C tau_f = c' + sigma_n/tan(phi'), independent of pore-water pressure. D tau_f = (sigma_n - u)/(c' + tan(phi')).

Question 2 ప్రశ్న 2

On a graph of shear strength against effective normal stress, which interpretation of the linear Mohr-Coulomb failure envelope is correct?

A The intercept on the shear-stress axis equals the effective friction angle, while the slope equals cohesion. B The envelope must always pass through the origin for every type of soil. C The slope represents pore-water pressure, while the intercept represents total vertical stress. D The intercept on the shear-stress axis is c', while the slope is tan(phi').

Question 3 ప్రశ్న 3

A soil has effective cohesion c' = 20 kPa and tan(phi') = 0.50. If the effective normal stress on a potential failure plane is 140 kPa, what is the shear strength?

A 70 kPa. B 80 kPa. C 90 kPa. D 110 kPa.

Question 4 ప్రశ్న 4

At a potential failure plane in saturated soil, total normal stress is 220 kPa and pore-water pressure is 70 kPa. The soil parameters are c' = 15 kPa and tan(phi') = 0.40. What is the effective-stress shear strength?

A 75 kPa. B 87 kPa. C 103 kPa. D 163 kPa.

Question 5 ప్రశ్న 5

A saturated clean sand is idealized as having zero effective cohesion and an effective friction angle of 30 degrees. If the effective normal stress on a shear plane is 180 kPa, what is its drained shear strength? Take tan(30 degrees) = 0.57735.

A 90.0 kPa. B 103.9 kPa. C 120.0 kPa. D 180.0 kPa.

Question 6 ప్రశ్న 6

Two drained direct shear tests give failure shear stresses of 70 kPa and 110 kPa at effective normal stresses of 100 kPa and 200 kPa, respectively. Assuming a linear Mohr-Coulomb envelope, determine c' and phi'.

A c' = 20 kPa and phi' = 30.0 degrees. B c' = 30 kPa and phi' = 30.0 degrees. C c' = 40 kPa and phi' = 21.8 degrees. D c' = 30 kPa and phi' = 21.8 degrees.

Question 7 ప్రశ్న 7

A saturated cohesionless soil has tan(phi') = 0.50 and a constant total normal stress of 200 kPa on a specified plane. If positive pore-water pressure increases from 40 kPa to 100 kPa, by how much does its effective-stress shear strength decrease?

A 15 kPa. B 20 kPa. C 30 kPa. D 60 kPa.

Question 8 ప్రశ్న 8

A saturated clay is idealized by a total-stress undrained friction angle phi_u = 0 degrees and undrained shear strength su = 45 kPa. What shear strengths are predicted by this model at total normal stresses of 100 kPa and 200 kPa, respectively?

A 45 kPa and 45 kPa. B 45 kPa and 90 kPa. C 100 kPa and 200 kPa. D 145 kPa and 245 kPa.

Question 9 ప్రశ్న 9

A rapidly constructed embankment imposes a substantial new load on a thick, saturated, low-permeability clay foundation. Which strength assessment is generally most appropriate for evaluating the immediate end-of-construction condition?

A Use only the drained friction angle because all applied load is immediately carried by the soil skeleton. B Use the dry-soil angle of repose as the sole shear-strength parameter. C Ignore the soil strength because excess pore-water pressure prevents all resistance to shear. D Evaluate undrained behaviour using representative undrained shear strength and a consistent total-stress analysis.

Question 10 ప్రశ్న 10

Which statement correctly describes the drainage conditions used in conventional UU, CU and CD triaxial compression tests?

A UU allows drainage during both consolidation and shearing, while CD prevents drainage throughout. B UU prevents drainage in both stages, CU allows consolidation drainage but prevents drainage during shearing, and CD allows drainage during consolidation and shearing. C UU permits drainage only during shearing, CU prevents all drainage, and CD permits drainage only during initial loading. D All three tests use identical drainage conditions and differ only in specimen diameter.

Question 11 ప్రశ్న 11

A series of saturated clay specimens is tested using consolidated-undrained triaxial compression with pore-water pressure measurements at failure. Which conclusion is correct regarding determination of strength parameters?

A Only the soil permeability can be obtained because undrained shearing cannot generate shear-strength data. B The measured pore-water pressure must be added to total principal stresses to obtain effective principal stresses. C Total-stress failure results are available, and effective-stress failure parameters can also be evaluated by subtracting measured pore-water pressures from total stresses. D The effective friction angle must be zero because drainage is prevented during shearing.

Question 12 ప్రశ్న 12

In a conventional UU triaxial compression test on saturated clay, the total major and minor principal stresses at failure are 260 kPa and 100 kPa, respectively. Assuming the phi_u = 0 total-stress model, what is the undrained shear strength?

A 80 kPa. B 100 kPa. C 160 kPa. D 180 kPa.

Question 13 ప్రశ్న 13

An unconfined compression test on a saturated clay specimen gives an unconfined compressive strength qu = 140 kPa. Under the conventional phi_u = 0 undrained interpretation, what is the undrained shear strength?

A 35 kPa. B 140 kPa. C 280 kPa. D 70 kPa.

Question 14 ప్రశ్న 14

During a direct shear test, the horizontal shear force at failure is 0.48 kN and the corrected area of the shear plane at failure is 60 cm². What is the shear stress at failure?

A 60 kPa. B 70 kPa. C 80 kPa. D 100 kPa.

Question 15 ప్రశ్న 15

A saturated soil has c' = 10 kPa and phi' = 30 degrees. The total normal stress on a plane is 200 kPa, and the pore-water pressure is 80 kPa. Using tan(30 degrees) = 0.57735, determine its effective-stress shear strength.

A 69.3 kPa. B 79.3 kPa. C 115.5 kPa. D 125.5 kPa.

Question 16 ప్రశ్న 16

On a potential slip plane, total normal stress is 220 kPa and the applied shear stress is 80 kPa. Soil strength parameters are c' = 10 kPa and tan(phi') = 0.50. Assuming these parameters remain constant, what positive pore-water pressure would bring the plane exactly to the Mohr-Coulomb failure condition?

A 80 kPa. B 60 kPa. C 100 kPa. D 140 kPa.

Question 17 ప్రశ్న 17

A cohesionless soil follows the effective-stress Mohr-Coulomb criterion with phi' = 30 degrees. In a triaxial compression test at failure, the minor effective principal stress is 100 kPa. What is the major effective principal stress at failure?

A 150 kPa. B 200 kPa. C 250 kPa. D 300 kPa.

Question 18 ప్రశ్న 18

Under the conventional Mohr-Coulomb triaxial compression failure model, what angle does the theoretical shear failure plane make with the major principal plane when the friction angle is 30 degrees?

A 30 degrees. B 60 degrees. C 45 degrees. D 75 degrees.

Question 19 ప్రశ్న 19

The major and minor effective principal stresses at a point are 260 kPa and 100 kPa, respectively. What are the centre and radius of the corresponding Mohr circle in the effective normal stress-shear stress plane?

A Centre = 160 kPa; radius = 100 kPa. B Centre = 80 kPa; radius = 180 kPa. C Centre = 180 kPa; radius = 80 kPa. D Centre = 260 kPa; radius = 100 kPa.

Question 20 ప్రశ్న 20

On a specified potential sliding plane, the total normal stress is 180 kPa, pore-water pressure is 20 kPa and applied shear stress is 70 kPa. The effective strength parameters are c' = 10 kPa and tan(phi') = 0.50. What is the factor of safety defined as available shear strength divided by applied shear stress on this plane?

A 1.29. B 1.00. C 1.14. D 1.57.

Question 21 ప్రశ్న 21

A soil has effective cohesion 10 kPa and tan(phi') = 0.50. If effective normal stress on a potential shear plane increases from 120 kPa to 200 kPa without changing the strength parameters, what is the increase in shear strength?

A 20 kPa. B 30 kPa. C 80 kPa. D 40 kPa.

Question 22 ప్రశ్న 22

Which statement best distinguishes peak shear strength from residual shear strength in a soil exhibiting strain-softening behaviour?

A Residual shear strength is always greater than peak shear strength because particle orientation continually increases resistance. B Peak strength is the maximum resistance mobilized during shearing, while residual strength is the lower resistance that may develop after large shear displacements. C Peak and residual strengths must always be identical for overconsolidated clays. D Residual strength can be measured only before any shear displacement occurs.

Question 23 ప్రశ్న 23

For dense and loose specimens of the same sand tested under comparable drained effective-stress conditions, which statement is generally correct?

A Loose sand always develops a higher peak friction angle because its void ratio is greater. B Dense and loose sand must have identical stress-strain curves at every strain level. C Dense sand commonly exhibits dilation and a pronounced peak shear resistance, whereas loose sand more commonly contracts during shearing. D Dense sand behaves as a purely cohesive material with zero effective friction angle.

Question 24 ప్రశ్న 24

A partially saturated soil exhibits an apparent cohesion intercept associated with capillary suction. Which engineering interpretation is most appropriate when the soil becomes substantially wetter?

A Apparent cohesion caused by suction must remain unchanged regardless of the soil water condition. B Wetting necessarily increases effective cohesion by the same amount as the increase in total water content. C Capillary suction can be treated as permanent cementation that cannot be reduced by infiltration. D Wetting can reduce matric suction and the associated apparent shear-strength contribution, so stability should not rely on that contribution remaining constant.

Question 25 ప్రశ్న 25

On a potential shear plane in saturated soil, initial total normal stress is 150 kPa and initial pore-water pressure is 50 kPa. A subsequent loading stage increases total normal stress by 80 kPa and pore-water pressure by 60 kPa. If c' = 10 kPa and tan(phi') = 0.50 remain unchanged, how does the effective-stress shear strength change?

A It increases from 60 kPa to 70 kPa. B It decreases from 60 kPa to 50 kPa. C It increases from 60 kPa to 100 kPa. D It remains constant at 60 kPa.

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