NICET CMT Soils flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Liquid limit (LL)

Water content at which soil transitions from plastic to liquid state, determined at 25 blows in Casagrande device or by fall cone; key for plasticity and classification.

Plasticity index (PI)

PI = LL − PL; range of water content over which soil remains plastic; high PI indicates clay and potential volume change.

USCS gravel-sand boundary

In USCS, gravel is retained on 4.75 mm (No. 4) sieve; sand passes 4.75 mm and is retained on 0.075 mm (No. 200) sieve.

AASHTO group index

GI = (F−35)[0.2+0.005(LL−40)] + 0.01(F−15)(PI−10), where F is percent passing 0.075 mm; higher GI means poorer subgrade performance.

Standard Proctor energy

Standard Proctor (ASTM D698) applies 12,400 ft·lbf/ft³ (600 kN·m/m³) using 2.5 kg hammer, 305 mm drop, 3 layers, 25 blows.

Modified Proctor energy

Modified Proctor (ASTM D1557) applies 56,250 ft·lbf/ft³ (2,700 kN·m/m³) using 4.54 kg hammer, 457 mm drop, 5 layers, 25 blows.

Zero air voids curve

Theoretical curve γd = Gs·γw/(1 + w·Gs/Sr) at Sr = 100%; no field compaction point can plot to the right of this curve.

Specific gravity (Gs)

Ratio of soil particle density to water density; typically 2.65–2.75 for mineral soils; used in phase relations and ZAV curve.

CBR test

California Bearing Ratio: penetration resistance of compacted, soaked sample at 2.5 mm and 5.0 mm compared to standard crushed stone; expressed as percent.

Hydrometer analysis

Sedimentation test using Stokes' law to determine particle size distribution of fines passing 0.075 mm; measures density of suspension over time.

Sand cone test

ASTM D1556 field density method: volume of hole determined by calibrated sand; dry unit weight = dry soil mass divided by hole volume.

Nuclear gauge density test

ASTM D6938 method using gamma radiation to measure wet density and moisture; must be calibrated to sand cone and corrected for trench effects.

Relative compaction

RC = (field dry unit weight ÷ lab maximum dry unit weight) × 100; typical specification 95% standard Proctor for fill.

Optimum moisture content (OMC)

Water content at which a given compaction effort produces maximum dry unit weight; varies with soil type and compaction energy.

Oven-dry moisture method

Standard moisture determination: dry soil at 110 ± 5°C to constant mass; water content = (wet mass − dry mass) / dry mass × 100.

One-point Proctor

Field compaction test at one moisture content; uses family of curves to estimate maximum dry unit weight and OMC for that soil.

Rubber balloon test

ASTM D2167 field density method: volume of test hole measured by water-filled balloon; suitable for coarse or hard soils.

Compaction test frequency

Typical specification: one field density test per 500–1,000 m² per lift or per 100–200 m of trench; verify project-specific requirements.

Lift thickness

Loose soil layer thickness before compaction; typically 150–300 mm for embankment; must not exceed effective compaction depth.

Proof-rolling

Inspection by rolling loaded equipment over prepared subgrade to identify soft spots, pumping, or rutting that require repair before fill placement.

Benching embankment slopes

Cutting horizontal steps into existing slope before placing new fill to ensure bonding and prevent slip failure between fill and original ground.

Frozen fill prohibition

Frozen soil, snow, or ice must not be placed in fill; thawing causes settlement, low density, and instability.

Backfill compaction

Placing and compacting backfill in thin lifts on both sides of structures to prevent unbalanced loads and ensure density around utilities.

Subgrade preparation

Removing topsoil and organics, scarifying, moisture-conditioning, compacting, and verifying grade and crown before placing base or fill.

Fill slope ratio

Embankment side slope typically 1V:2H to 1V:3H; flatter slopes improve stability and reduce erosion; verify project specifications.

Inspection record content

Log lift number, location, material source, moisture, density test results, and acceptance status for each lift placed.

Undisturbed sampling

Thin-walled Shelby tube or block sample taken without disturbing structure; sealed with wax, labeled with orientation, and transported carefully.

Disturbed sampling

Bag or bulk sample for classification, Proctor, or other tests where structure is not preserved; protect from moisture loss and contamination.

Test report requirements

Report must include sample ID, test method, results, calibration, deviations, technician, date, and remarks; retain raw data.

Specification hierarchy

Contract drawings and specifications govern; standard test methods apply as referenced; conflicts must be resolved in writing by the engineer.

Ethical reporting

Report data accurately, never alter or discard results, disclose test deviations and calibration issues, and maintain confidentiality of client data.

Chain of custody

Documented record of sample handling from collection through testing; required for forensic or dispute work to ensure integrity.