NICET Geotech common mistakes
NICET Geotech · Understand the traps and how to avoid them.
Treating the Atterberg limits as one number - memorizing 'CL' or 'CH' by name - instead of computing plasticity index as LL minus PL and then placing the soil on the Casagrande A-line using both PI and LL together.
Candidates study classification by memorizing the USCS chart visually and never practice the arithmetic under time pressure, so they misplace borderline soils (e.g., PI just above or below the A-line) and miss that a soil with LL = 50 exactly is 'L' not 'H'.
What to do instead
Drill ten worked classification problems where you compute LL, PL, PI, and the A-line PI (0.73 × (LL − 20)) side by side, then state the group symbol and name. Practice the boundary rules explicitly: LL of 50 is low-plasticity, and the A-line comparison uses the rounded PI.
Reporting a compaction test result as a single dry unit weight without stating the optimum moisture content, or reading the peak of the curve at the highest tested point when the curve is still rising at the edge of the data.
Candidates see a bell-shaped curve in study material and assume every field curve has a clean interior peak; real curves can peak outside the tested range, requiring extrapolation or a retest, and the exam expects you to recognize the paired nature of maximum dry density and OMC.
What to do instead
Always report the pair (maximum dry density and optimum moisture content) and check whether the peak is bracketed by at least two points on each side. Practice computing dry unit weight from wet unit weight and moisture content (γd = γ / (1 + w)) so you can build the curve from raw scale data rather than reading it off a figure.
Confusing relative compaction with relative density, or applying the field compaction specification to the wrong reference - dividing field dry density by the maximum dry density from a different compactive effort (e.g., Standard vs. Modified Proctor).
Both terms involve 'relative' and a comparison to a maximum, and laboratory reports may list both Standard and Modified Proctor values, so candidates grab whichever number appears first without checking which effort the specification cites.
What to do instead
Write the definition before calculating: relative compaction = field γd ÷ lab maximum γd for the specified effort, expressed as a percentage. Confirm the specification's compactive effort (ASTM D698 Standard vs. D1557 Modified) before dividing, and keep the two lab maxima labeled in your notes.
Using total stress or total unit weight in a bearing capacity or slope stability calculation where the water table is present, instead of substituting effective stress and buoyant (submerged) unit weight below the water table.
Candidates learn the Terzaghi bearing capacity equation with γ and then apply it mechanically; the water table correction is a small step that is easy to skip, and the problem statement often buries the groundwater depth in a sentence.
What to do instead
Before any bearing or slope calculation, sketch the profile, mark the water table, and label each layer's unit weight as total above and buoyant below (γ′ = γsat − γw). Practice three problems where the water table sits at different depths (above footing base, at base, below base) so the correction becomes automatic.
Misreading a boring log - treating the blow counts from a split-spoon sample as if the sampler were driven continuously, or failing to correct field N-values for hammer energy, rod length, and sampler type before using them in correlations.
Logs present N-values in a depth column that looks continuous, and candidates use raw N directly in correlations (e.g., friction angle or settlement) without applying the correction to (N1)60, which changes the answer materially in loose or deep soils.
What to do instead
Practice reading a sample log and stating the depth interval each blow count represents (typically 6 in. seating, then 6 in. and 6 in. recorded). Then apply the standard corrections step by step and record both N and (N1)60, noting which one the correlation requires.
Skipping the sieve-versus-hydrometer consistency check - reporting a gradation curve where the percent passing the No. 200 sieve from the wash/sieve analysis does not match the percent finer from the hydrometer analysis.
The two tests are run and reported separately, and candidates plot both without reconciling the overlap, producing a curve with a vertical jump or offset at the No. 200 boundary that signals a data or dispersion error.
What to do instead
Always compare the percent passing No. 200 by sieving with the percent finer at the same particle size from the hydrometer, and investigate any discrepancy before plotting. Practice one full combined gradation so you know where the two data sets must join and how to adjust for dispersing agent or deflocculation differences.
Reporting a Proctor or CBR specimen's moisture content from the target moisture rather than from an oven-dry measurement of the actual specimen, or averaging moisture contents across specimens without tracking which specimen produced which density.
Candidates shortcut the moisture determination because the target value is written on the batch sheet, and the exam tests whether you understand that moisture content must be measured on the tested material, not assumed from the mix design.
What to do instead
For every density point, pair the measured oven-dry moisture with the measured dry density from the same specimen. Practice a data table where target and measured moisture differ, and compute the moisture from wet and dry masses (w = (Mwet − Mdry)/Mdry × 100) so the measurement path is habitual.
Applying a settlement or consolidation formula without distinguishing normally consolidated from overconsolidated clay - using the compression index Cc when the stress path stays below the preconsolidation pressure and the recompression index Cr governs.
The standard formula with Cc is the one most practiced, and the preconsolidation pressure is often given in a separate sentence or must be read from an e-log p curve, so candidates default to Cc and overestimate settlement.
What to do instead
Before computing, locate the preconsolidation pressure and compare the initial and final effective stresses to it. Practice three cases: stress range entirely below, entirely above, and crossing the preconsolidation pressure, so you can write the correct piecewise expression including both Cr and Cc segments.
Treating a permeability or seepage problem as a single-layer calculation when the flow passes through stratified soil, or forgetting to convert hydraulic conductivity units before computing the gradient or flow rate.
Layered systems require the harmonic mean for vertical flow and the arithmetic mean for horizontal flow, and candidates apply one formula to both directions; unit conversions between cm/s and ft/day are also a frequent silent error.
What to do instead
Draw the flow direction relative to bedding before choosing the averaging method, and write the formula with units attached at every step. Practice one vertical and one horizontal layered permeability problem side by side, plus a Darcy flow calculation where the conductivity is given in cm/s and the answer is requested in ft³/day.
Answering a field quality-control question with the laboratory acceptance criterion - for example, accepting a lift because the nuclear gauge reading matches the lab maximum density, without checking the specified relative compaction, lift thickness, or the required number of passes and proofrolling.
Candidates conflate 'the density looks right' with 'the work meets specification,' and the exam tests the field inspection role: sampling frequency, lift thickness limits, moisture conditioning at placement, and documentation, not just a single density number.
What to do instead
Build a one-page field QC checklist covering sampling frequency per volume of fill, required relative compaction, moisture tolerance at placement, maximum lift thickness, and acceptance versus rejection actions. Practice scenario questions where the density passes but another criterion (lift thickness or moisture) fails, so you learn to check all conditions before signing off.