CCIL CCIL - Canadian Council of Independent Laboratories Soil Testing and Geotechnical Analysis Questions and Answers 4 — Questions and Answers
Question 1: Which ASTM standard governs the laboratory determination of the shrinkage limit of fine-grained soils?
- ASTM D427 (Correct answer)
- ASTM D4318
- ASTM D2216
- ASTM D854
Correct answer: ASTM D427
ASTM D427 covers the test method for shrinkage factors of soils by the mercury method, defining the shrinkage limit.
Question 2: In a consolidated-undrained (CU) triaxial test, pore pressure measurements are used to calculate which parameter?
- Effective stress strength parameters (c' and φ') (Correct answer)
- Total stress cohesion only
- Compression index Cc
- Coefficient of uniformity Cu
Correct answer: Effective stress strength parameters (c' and φ')
CU tests with pore pressure measurement allow back-calculation of effective stress parameters c' and φ' from Mohr-Coulomb failure envelopes.
Question 3: According to ASTM D1556, what material is used as the filling medium in the sand cone density test?
- Ottawa sand passing No. 20 and retained on No. 30 sieve (Correct answer)
- Dry silica sand of any gradation
- Graded gravel 4.75 mm to 9.5 mm
- Fine-grained natural sand from the site
Correct answer: Ottawa sand passing No. 20 and retained on No. 30 sieve
ASTM D1556 specifies Ottawa sand (or equivalent) passing the No. 20 sieve and retained on the No. 30 sieve for consistent cone calibration.
Question 4: What does the term 'sensitivity' refer to when describing cohesive soils?
- Ratio of undisturbed to remolded undrained shear strength (Correct answer)
- Rate of consolidation under applied load
- Change in plasticity index with water content
- Degree of cementation between soil particles
Correct answer: Ratio of undisturbed to remolded undrained shear strength
Sensitivity (St) is the ratio of undisturbed peak undrained shear strength to remolded undrained shear strength at the same water content.
Question 5: Which sieve size defines the boundary between gravel and sand in the Unified Soil Classification System (USCS)?
- No. 4 (4.75 mm) (Correct answer)
- No. 10 (2.0 mm)
- No. 40 (0.425 mm)
- No. 200 (0.075 mm)
Correct answer: No. 4 (4.75 mm)
The USCS uses the No. 4 sieve (4.75 mm opening) as the boundary between gravel and sand particle sizes.
Question 6: In a falling-head permeability test, what must remain constant throughout the test?
- Cross-sectional area of the standpipe (Correct answer)
- Hydraulic gradient across the sample
- Water temperature and sample void ratio
- Head difference between inlet and outlet
Correct answer: Cross-sectional area of the standpipe
The standpipe area (a) is a fixed geometric parameter in the falling-head formula k = (aL/At) × ln(h1/h2).
Question 7: What is the primary purpose of back-pressure saturation in triaxial testing?
- To dissolve air bubbles and achieve near-100% saturation in the sample (Correct answer)
- To increase confining stress on the specimen
- To measure pore pressure at failure
- To consolidate the sample faster under higher stress
Correct answer: To dissolve air bubbles and achieve near-100% saturation in the sample
Back pressure forces air into solution in pore water, driving Skempton's B value toward 1.0 and ensuring full saturation before shearing.
CCIL CCIL - Canadian Council of Independent Laboratories Soil Testing and Geotechnical Analysis Questions and Answers 4
Which ASTM standard governs the laboratory determination of the shrinkage limit of fine-grained soils?