Civil Engineering: Structural, Geotechnical, Water and Transportation Design
Civil Engineering in IESL Part III spans structural analysis and reinforced concrete design, soil mechanics and foundation design, hydraulics and water resources, transportation and surveying, and construction materials and quality control.
Core rules and concepts
- Structures: use limit state design with factored load combinations, and check both ultimate (bending, shear, bond, deflection is serviceability) and serviceability criteria. For a simply supported beam, M = wL²/8 under uniformly distributed load; design steel from M ≈ 0.87 fy As × lever arm, with lever arm near 0.9d for lightly reinforced sections.
- Geotechnics: bearing capacity from Terzaghi/Meyerhof with shape and depth factors; use effective (submerged) unit weight below the water table; check settlement, not only capacity; retaining walls need stability against overturning, sliding and bearing failure.
- Hydrology: the rational method Q = C·i·A/360 for Q in m³/s, i in mm/h and A in hectares; unit hydrographs for larger catchments.
- Transportation: horizontal curve radius from R = V²/(127(e + f)) with consistent units.
- Surveying: reduce levels from a benchmark, close the traverse, and distribute misclosure before computing coordinates.
Worked example
A simply supported RC beam spans 6.0 m clear, carries a design UDL of 20 kN/m, with b = 300 mm, d = 500 mm and fy = 460 N/mm². Design moment M = wL²/8 = 20 × 36/8 = 90 kNm. Taking the lever arm as 0.90d = 450 mm, As = M/(0.87 fy × 0.90d) = 90 × 10⁶/(0.87 × 460 × 450) ≈ 500 mm². That is roughly 2T20 (628 mm²), then verify minimum steel, maximum steel, shear links and deflection.
Traps that cost marks
Mixing kNm with N·mm; using clear span where the code requires effective span; using total unit weight below the water table; forgetting the units inside the rational method constant; and treating bearing capacity as the only geotechnical check.