Geotechnical Analysis, Design, and Construction Considerations
What to know
This domain tests judgment across the design–build interface. Understand ASD versus LRFD: LRFD applies load factors greater than one to loads and resistance factors less than one to nominal resistances, checking ΣγiQi ≤ φRn. Know typical resistance factors for bearing capacity (roughly 0.45–0.65) and driven piles (roughly 0.5–0.75) so you can spot a misplaced factor.
Construction topics recur: dewatering (wellpoints, deep wells, cutoffs), ground improvement (stone columns, wick drains with surcharge, dynamic compaction, compaction and permeation grouting, deep soil mixing), and earthwork control (lift thickness, moisture within a few percent of optimum, relative compaction specified as a percentage of maximum dry density from the standard lab test). Instrumentation - settlement plates, inclinometers, piezometers, extensometers - drives observational design.
Also know expansive soil mitigation (overexcavation and replacement, moisture barriers), frost depth and heave, liquefaction mitigation, vibration and settlement monitoring for adjacent structures, and the difference between a design change and a differing site condition.
Traps
Mixing relative compaction with relative density; forgetting shrinkage and swell when converting cut, loose, and compacted volumes; and applying resistance factors to loads instead of resistances.
Worked example
Cut 10,000 cy bank. Fill required: 8,000 cy compacted, with 15% shrinkage, so bank volume needed = 8,000/0.85 ≈ 9,410 cy. Surplus = 10,000 − 9,410 ≈ 590 cy in bank measure. If the surplus is hauled with 25% swell, it occupies about 740 cy loose.