Geotechnical Engineering and Foundations
Geotechnical questions in the Egyptian consultant exam test whether you can interpret a soil investigation, choose a foundation type, and check both bearing capacity and settlement under ECP 202. The exam often uses shallow footings, piles, retaining walls and groundwater problems where the governing issue is not strength alone but serviceability and construction method.
Core rules and concepts
- Site investigation: boreholes, trial pits, SPT, CPT and laboratory tests define stratification, groundwater level, strength and compressibility. The foundation design must reflect the actual borehole log, not a single average soil type.
- Bearing capacity: for shallow foundations, compute ultimate bearing capacity using drained or undrained parameters, then apply a factor of safety. ECP 202 practice commonly uses a global factor of about 3 for static shallow foundations, with settlement checked separately.
- Settlement: immediate and consolidation settlement must stay within code limits; differential settlement is often more damaging than total settlement.
- Piles: capacity is the sum of shaft friction and end bearing, reduced by group effects; negative skin friction and uplift must be checked where fill or groundwater lowering occurs.
- Retaining walls: check overturning, sliding, bearing and global stability, using active and passive earth pressures and water pressure separately.
Worked example
A strip footing 2.0 m wide is founded at 1.5 m depth in soil with c = 20 kPa, φ = 25°, and bulk unit weight 18 kN/m³. Above the water table, use Terzaghi factors Nc = 25.1, Nq = 12.7, Nγ = 9.7. The surcharge is q = γDf = 18 × 1.5 = 27 kPa. Then qu = cNc + qNq + 0.5γBNγ = 20(25.1) + 27(12.7) + 0.5(18)(2)(9.7) = 502 + 342.9 + 174.6 = 1019.5 kPa. With a factor of safety of 3, qall = 340 kPa. This is a strength check only; settlement, eccentricity and groundwater must still be verified.
Traps that cost marks
- Using total unit weight below the water table instead of submerged unit weight.
- Applying a bearing-capacity factor of safety and then treating the result as a settlement limit.
- Ignoring eccentric load or inclined load reductions.
- Designing a pile group from single-pile capacity without group efficiency and block failure checks.
- Forgetting construction-stage stability for excavations and retaining walls.