Test 20 - Soil Sampling and In-Situ Testing

Question 1 ప్రశ్న 1

A proposed raft foundation is underlain by soft saturated clay. The engineer needs samples for determining natural compressibility, consolidation characteristics and stress history. Which sampling strategy is most appropriate?

A Collect only loose soil cuttings from rotary drilling and remould them before every test. B Obtain high-quality relatively undisturbed clay samples using a suitable thin-walled or piston sampler and assess their condition before testing. C Use only dry soil collected from the excavation surface because groundwater does not affect consolidation. D Obtain SPT split-spoon samples and assume that their natural structure is perfectly preserved.

Question 2 ప్రశ్న 2

A disturbed soil sample is collected below the groundwater table for natural water-content determination and soil identification. Which handling procedure is most appropriate?

A Leave the sample exposed to sunlight until it reaches constant mass before recording its natural water content. B Mix the sample with dry soil from another depth to obtain an average water content. C Add water until the specimen appears saturated and then label it as a natural sample. D Place the sample promptly in a properly sealed and labelled moisture-resistant container, recording its origin and sampling depth.

Question 3 ప్రశ్న 3

The cutting edge of a thin-walled soil sampler has an outside diameter of 80 mm and an inside diameter of 76 mm. Using area ratio Ar = [(Do² - Di²)/Di²] × 100, what is the sampler area ratio?

A 10.8%. B 5.0%. C 20.5%. D 25.0%.

Question 4 ప్రశ్న 4

A very soft saturated clay deposit must be sampled at considerable depth for laboratory strength and consolidation tests. Which method is generally preferred for reducing disturbance caused by sampler penetration and withdrawal?

A Aggressive wash boring with only the returned cuttings preserved. B Repeated driving of a thick-walled open sampler using large impact forces. C Carefully controlled piston sampling with an appropriate thin-walled tube and proper sample preservation. D Collecting remoulded clay from the drilling-fluid settling tank.

Question 5 ప్రశ్న 5

Two samplers of similar diameter are proposed for obtaining cohesive-soil specimens. Sampler A has a substantially smaller cutting-edge area ratio than Sampler B, while other sampling conditions are comparable. Which conclusion is most technically defensible?

A Sampler A is generally more favourable for reducing displacement-related disturbance, but area ratio alone cannot guarantee sample quality. B Sampler B must always recover a perfectly undisturbed sample because more metal contacts the soil. C Both samplers necessarily produce identical disturbance regardless of their cutting-edge geometry. D Area ratio determines the soil's natural permeability and is unrelated to sampling.

Question 6 ప్రశ్న 6

A tube sampler is pushed 0.60 m into a cohesive soil layer, but the recovered soil specimen has a length of 0.45 m. What is the sample recovery ratio, expressed as a percentage, and what is the appropriate interpretation?

A 60%; the sample is necessarily undisturbed. B 75%; the soil must be cohesionless. C 133.3%; the sampler has experienced excessive recovery. D 75%; incomplete recovery should be recorded, and recovery percentage alone does not establish sample quality.

Question 7 ప్రశ్న 7

A borehole investigation produces disturbed soil samples from several clay layers. Which proposed laboratory-testing programme makes the most appropriate use of these samples without assuming that their natural structure is preserved?

A Determine the undisturbed preconsolidation pressure from remoulded specimens without qualification. B Conduct soil classification, grain-size and Atterberg-limit tests where suitable, while obtaining higher-quality specimens for representative natural-structure consolidation testing. C Use the disturbed samples directly to establish the exact in-situ stiffness of every layer. D Assume all laboratory strength results from remoulded samples represent the original intact clay strength.

Question 8 ప్రశ్న 8

During a Standard Penetration Test, the recorded blow counts for three successive 150 mm penetration increments are 6, 10 and 14. Assuming the full penetration is achieved without refusal, what is the uncorrected field SPT N-value?

A 14. B 20. C 24. D 30.

Question 9 ప్రశ్న 9

Which combination correctly describes the nominal hammer mass, free-fall height and penetration interval used to determine the SPT N-value under the current Indian SPT method?

A 63.5 kg hammer, 750 mm fall and blows for 300 mm penetration after a 150 mm seating drive. B 50 kg hammer, 500 mm fall and blows for the first 150 mm penetration only. C 63.5 kg hammer, 750 mm fall and blows for the entire 450 mm penetration including the seating drive. D 100 kg hammer, 1000 mm fall and blows for a continuous 1 m penetration.

Question 10 ప్రశ్న 10

An SPT performed in sand gives a field N-value of 24. The measured hammer energy efficiency is 45%, and the specified normalization is N60 = N × (ER/60%), with all other equipment correction factors taken as unity. What is N60?

A 12. B 16. C 18. D 32.

Question 11 ప్రశ్న 11

A field SPT N-value in a cohesionless deposit is 20. The measured hammer energy efficiency is 75%, the reference efficiency is 60%, and the specified effective-overburden correction factor CN is 1.20. Taking all other equipment factors as unity, what is the energy-corrected and overburden-normalized value (N1)60?

A 20. B 24. C 25. D 30.

Question 12 ప్రశ్న 12

For saturated fine sand below the groundwater table, the specified Indian SPT correction sequence has produced an overburden-corrected value of 31. Using the stated dilatancy correction Ncorrected = 15 + 0.5(Nprevious - 15) when Nprevious exceeds 15, what is the corrected value?

A 15. B 23. C 31. D 46.

Question 13 ప్రశ్న 13

During an SPT drive, 50 hammer blows produce only 40 mm of sampler advancement in a dense deposit containing possible coarse fragments. What is the most appropriate field interpretation?

A Report an ordinary completed N-value of exactly 50 for the full 300 mm test drive. B Assume that the material is definitely continuous sound bedrock. C Record the penetration and blow-count details as a refusal condition and investigate the possible cause before selecting design parameters. D Ignore the observation and assign an N-value of zero.

Question 14 ప్రశ్న 14

An SPT borehole is advanced into saturated sand below the groundwater table. Which drilling precaution is particularly important to avoid an artificially low penetration resistance caused by disturbance at the borehole bottom?

A Maintain adequate water or drilling-fluid head in the borehole and clean the bottom without causing loosening or upward piping. B Lower the borehole water level below the external groundwater head immediately before testing. C Jet water aggressively through the sampler during penetration to remove soil resistance. D Drive the casing below the test level so the sampler penetrates only previously disturbed material.

Question 15 ప్రశ్న 15

Two nearby SPTs in a nominally similar sand layer produce markedly different field N-values. The drilling logs also show differences in borehole stability, hammer energy and the presence of gravel. Which engineering response is most defensible?

A Treat both uncorrected N-values as exact and directly interchangeable measurements of friction angle. B Discard all geological information and adopt the arithmetic average as the final design parameter. C Select the larger N-value because it always represents the safer foundation design. D Review test execution, energy normalization, soil variability and possible gravel interference before developing representative design parameters.

Question 16 ప్రశ్న 16

During a static cone penetration test, the measured force on the cone tip is 20 kN and the projected cone base area is 1000 mm². Neglecting any pore-pressure area correction, what is the cone-tip resistance qc?

A 2 MPa. B 20 MPa. C 200 MPa. D 0.20 MPa.

Question 17 ప్రశ్న 17

A cone penetration test records cone-tip resistance qc = 10 MPa and sleeve-friction stress fs = 100 kPa at a particular depth. Using friction ratio Rf = (fs/qc) × 100%, what is Rf?

A 1.0%. B 0.1%. C 10.0%. D 100.0%.

Question 18 ప్రశ్న 18

A foundation investigation requires closely spaced resistance measurements through alternating sand and clay layers. Which comparison between CPT and SPT is most appropriate?

A SPT provides a perfectly continuous resistance profile without disturbing any soil. B CPT routinely provides intact soil samples suitable for every laboratory consolidation test. C CPT can provide a near-continuous penetration-resistance profile, while SPT provides discrete blow counts and recovered disturbed samples at selected depths. D Neither CPT nor SPT can provide any information about changes in soil strata.

Question 19 ప్రశ్న 19

During a piezocone penetration test, a CPTu system records cone resistance, sleeve friction and pore-water pressure. Which interpretation of the additional pore-pressure measurement is technically correct?

A The recorded pore pressure must always be equal to the long-term hydrostatic groundwater pressure. B Pore-pressure measurement eliminates the need to consider soil drainage conditions. C The pore-pressure response alone determines the exact mineral composition of every soil layer. D The pore-pressure response helps distinguish drainage behaviour and soil response during penetration, while dissipation observations can provide additional information about groundwater and consolidation behaviour.

Question 20 ప్రశ్న 20

For a saturated clay, an empirical CPTu interpretation uses su = (qt - sigma_v0)/Nk. At the test depth, corrected cone resistance qt = 2.4 MPa, total vertical overburden stress sigma_v0 = 0.4 MPa and the project-adopted cone factor Nk = 15. What is the estimated undrained shear strength su?

A 80.0 kPa. B 133.3 kPa. C 160.0 kPa. D 200.0 kPa.

Question 21 ప్రశ్న 21

In an in-situ vane shear investigation of soft saturated clay, the measured undisturbed undrained shear strength is 50 kPa. After remoulding the soil at essentially the same water content, the measured undrained strength is 12.5 kPa. What is the soil sensitivity, and what does it indicate?

A Sensitivity = 4.0; the undisturbed soil has four times the remoulded strength. B Sensitivity = 0.25; remoulding increases the shear strength fourfold. C Sensitivity = 37.5; sensitivity is the difference between the two strengths. D Sensitivity = 62.5; sensitivity is the sum of the two strengths.

Question 22 ప్రశ్న 22

A square steel plate measuring 0.50 m by 0.50 m is used in a field plate-load test. A centrally applied vertical load of 45 kN produces a recorded settlement of 5 mm. What is the corresponding average contact pressure beneath the plate?

A 90 kPa. B 112.5 kPa. C 225 kPa. D 180 kPa.

Question 23 ప్రశ్న 23

A plate-load test records a settlement of 6 mm at contact pressure 150 kPa and 12 mm at 240 kPa. Assume straight-line interpolation between these two measured points only. What contact pressure corresponds to an interpolated plate settlement of 10 mm?

A 180 kPa. B 195 kPa. C 210 kPa. D 225 kPa.

Question 24 ప్రశ్న 24

A plate-load test performed on the founding stratum gives a favourable load-settlement response. However, borehole information indicates a thick compressible clay layer beneath the depth substantially influenced by the small test plate but within the stress-influence zone of the proposed large raft. Which conclusion is most appropriate?

A The plate-test settlement is automatically equal to the final settlement of the raft. B The plate-load result must be supplemented by investigation and settlement analysis of the deeper clay because the full foundation influences a larger soil volume. C The underlying clay can be ignored because it is not directly in contact with the plate. D The plate-load test proves that consolidation settlement cannot occur.

Question 25 ప్రశ్న 25

Two properly isolated piezometers are installed in hydraulically connected soil at different elevations. Their screened measuring points are vertically separated by 3.0 m, with the upper piezometer recording hydraulic-head elevation +105.0 m and the lower recording +103.0 m relative to the same datum. Assuming predominantly vertical flow between the points, what are the magnitude of the average vertical hydraulic gradient and the likely flow direction?

A 0.667 downward. B 0.667 upward. C 1.500 downward. D 2.000 upward.

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