NICET Geotech cheat sheet

Civil Engineering Technology - Soils (CMT-Soils)

• Sieve analysis applies to particles retained on the No. 200 (0.075 mm) sieve; hydrometer analysis covers the finer fraction passing it. Percent passing is plotted on a semi-log gradation curve with sieve size (mm) on the log x-axis.

• Atterberg limits: liquid limit (LL) is the water content at 25 blows in the Casagrande cup; plastic limit (PL) is the water content where a 3.2 mm thread crumbles; plasticity index PI = LL − PL.

• Classification: AASHTO uses PI, LL, and percent passing No. 10, No. 40, and No. 200 sieves; USCS uses percent passing No. 200, LL, PI, and Cu/Cc from the gradation curve to assign group symbols (e.g., CL, CH, SM, SC, GP, GW).

• Compaction: Standard Proctor (ASTM D698) uses a 2.5 kg rammer, 305 mm drop, three layers, 600 kN·m/m³ energy; Modified Proctor (ASTM D1557) uses a 4.54 kg rammer, 457 mm drop, five layers, 2700 kN·m/m³ energy.

• Field density: sand cone (ASTM D1556) and nuclear gauge (ASTM D6938) measure in-place wet density; relative compaction = field dry density ÷ maximum dry density from the specified Proctor test, expressed as a percentage.

• Effective stress: σ′ = σ − u. Total vertical stress σ = Σγh; pore pressure u = γw·hw with γw ≈ 9.81 kN/m³ (62.4 pcf).

• Consolidation: coefficient of consolidation cv from the log-time (Casagrande) or square-root-time (Taylor) construction; overconsolidation ratio OCR = σ′p/σ′v0.

• Shear strength: Mohr–Coulomb τ = c′ + σ′·tan φ′. Direct shear (ASTM D3080) gives drained parameters; unconsolidated-undrained triaxial (ASTM D2850) gives total-stress parameters.

• Permeability: constant-head test for coarse soils (k = QL/(A·h·t)); falling-head test for fine soils; k is proportional to the square of the effective grain size (Hazen: k ≈ C·D10²).