NICET CMT Soils cheat sheet

Atterberg limits: LL = water content at 25 blows (Casagrande) or per fall cone; PL = water content at 3.2 mm thread; PI = LL − PL.

USCS: G gravel (>4.75 mm), S sand (0.075–4.75 mm), M silt, C clay, O organic, Pt peat; use Cu = D60/D10 and Cc = (D30)²/(D10·D60) for GW vs GP.

AASHTO: group index GI = (F−35)[0.2+0.005(LL−40)]+0.01(F−15)(PI−10); F = % passing 0.075 mm; report as A-1-a (0) etc.

Proctor compaction: standard = 12,400 ft·lbf/ft³ (600 kN·m/m³), modified = 56,250 ft·lbf/ft³ (2,700 kN·m/m³); peak dry unit weight at OMC.

Sieve analysis: wash #200 before nested sieves; record cumulative % passing; hydrometer for fines (<0.075 mm) using Stokes' law.

Specific gravity (Gs): pycnometer; typical 2.65–2.75 for mineral soils; used in phase relations and zero-air-voids curve.

Zero air voids curve: γd = Gs·γw / (1 + w·Gs/Sr); at Sr = 100% gives upper bound on compaction; compare field point to ZAV.

CBR: compact to target density, soak 4 days, measure penetration at 2.5 mm and 5.0 mm; report higher of ratios to standard loads (13.44 and 20.3 kN).

Organic content: loss on ignition at 440°C; high organics (e.g., >5–10%) degrade compaction and strength; classify as Pt or OH/OL.

Sand cone (ASTM D1556): calibrated sand density; volume = mass of sand in hole / sand bulk density; γd = dry mass / volume.

Nuclear gauge (ASTM D6938): direct transmission for density, backscatter for shallow; calibrate with sand cone; correct for moisture and trench effects.

Rubber balloon (ASTM D2167): volume by water-filled balloon; suitable for coarse or hard soils where sand cone is difficult.

Field moisture: oven-dry at 110 ± 5°C to constant mass; microwave or speedy moisture are rapid but require calibration.

Relative compaction RC = (γd field / γd max lab) × 100; typical spec 95% standard Proctor for fill, 98% for base.

Percent compaction relative to modified Proctor is lower for same field density; always match lab method (standard vs modified) to spec.

Test location frequency: often 1 per 500–1,000 m² per lift or per 100–200 m linear for trenches; verify project spec.

Reject a test if field moisture > OMC + 2% or < OMC − 2% unless spec allows; adjust with drying or water addition.

One-point Proctor (ASTM D698/D1557): compact at field moisture, use family of curves to estimate max dry unit weight and OMC.

Lift thickness: typically 150–300 mm loose for embankment; must not exceed depth of effective compaction (usually ≤ 300 mm).

Proof-rolling: observe for pumping, rutting, or soft spots; reject areas that deflect excessively under loaded equipment.

Subgrade preparation: remove topsoil and organics, scarify, moisture-condition, compact to spec, verify grade and crown.

Backfill to structures: use free-draining granular material unless spec allows; compact in lifts on both sides to prevent unbalanced load.

Trench backfill: place and compact in lifts; do not drop large lifts; check density at each lift and around utilities.

Embankment benching: cut steps into existing slope before placing new fill to ensure bonding; minimum bench width per spec.

Frozen material, snow, or ice must not be placed in fill; frozen lifts cause settlement and low density.

Slope stability: control fill slope (typically 1V:2H to 1V:3H), compact surface, and provide drainage to prevent erosion.

Inspection records: log lift number, location, material source, moisture, density test results, and acceptance status.

Disturbed samples: representative bag samples for classification and Proctor; avoid contamination and moisture loss.

Undisturbed samples: thin-walled tube (Shelby) or block; seal with wax, label with orientation, and transport without disturbance.

Sample labeling: project, location, depth, date, sampler, test requested; maintain chain-of-custody for forensic or dispute work.

Test report contents: sample ID, test method (ASTM/AASHTO), results, calibration, deviations, technician, date, and remarks.

Specification hierarchy: contract drawings and specifications govern; standard test methods apply as referenced; resolve conflicts in writing.

Ethics: report data accurately, never alter or discard results; disclose test deviations and calibration issues to the engineer.

Confidentiality: client data and test results are confidential; do not release without authorization.

Conflict of interest: disclose any relationship that could bias testing or inspection; decline work if impartiality is compromised.

Record retention: retain raw data, calibration records, and reports per contract and legal requirements (often 3–7 years).