Civil Engineering
Civil Engineering in SSC JE tests materials, surveying, estimating, soil and fluid mechanics, and structural behaviour at junior-engineer depth. Questions reward direct formula recall and unit discipline rather than long derivations.
Core rules
- Concrete nominal mixes are volume-based: M20 = 1:1.5:3, M15 = 1:2:4, M10 = 1:3:6. Design mixes are strength-based and need trial mixes.
- Workability is measured by slump, compaction factor, or Vee-Bee; slump is not a strength test.
- In levelling, reduce levels by height of instrument (HI) or rise-and-fall; always check arithmetic with ΣBS − ΣFS = last RL − first RL.
- Bearing capacity is a soil property; safe bearing capacity = ultimate bearing capacity / factor of safety.
- For a simply supported beam with central point load W and span L, maximum BM = WL/4 at midspan; shear is maximum at supports.
Worked example
Estimate cement for 1 m³ of finished M20 nominal concrete. Take dry-volume factor 1.54 and cement bulk density 1440 kg/m³. Total mix parts = 1 + 1.5 + 3 = 5.5. Cement volume = 1.54 × (1/5.5) = 0.28 m³. Cement mass = 0.28 × 1440 ≈ 403 kg, about 8 bags of 50 kg. The reasoning matters: the 1.54 factor converts wet placed volume to dry ingredients; skipping it understates cement by about 35%.
Traps
- Using wet volume directly in mix calculations.
- Mixing slump with compaction factor or calling slump a strength measure.
- Forgetting unit conversion in BM, stress, or discharge.
- Adding or subtracting levels in the wrong direction in levelling tables.