DDA JE Civil: Civil Engineering: Technical Core for DDA JE (Civil)

Civil Engineering is the technical core of the DDA JE (Civil) paper. It tests diploma-level applied knowledge across building materials, concrete technology, surveying, strength of materials, hydraulics, soil mechanics and quantity estimation, with DDA-relevant emphasis on CPWD-style specifications and urban development works.

Core rules you must be able to apply

• Concrete: nominal mixes M15 (1:2:4), M20 (1:1.5:3) and M25 (1:1:2) by volume; 150 mm cubes are tested at 28 days; characteristic strength is the value below which no more than 5% of results fall. Curing is 7 days for OPC and 14 days for blended cements.
• Surveying: reduce level = height of instrument minus staff reading; check levelling by ΣBS − ΣFS = last RL − first RL. Convert reduced bearing (RB) to whole-circle bearing (WCB) by quadrant: NE = RB; SE = 180° − RB; SW = 180° + RB; NW = 360° − RB.
• Strength of materials: stress = P/A, strain = ΔL/L, and the bending equation is M/I = σ/y = E/R.
• Soil: dry density γd = Gγw/(1+e); compaction peaks at OMC, and CBR is a penetration-strength index.
• Hydraulics: continuity Q = AV; Bernoulli applies along a streamline for steady ideal flow.

Worked example

A soil sample has G = 2.70, e = 0.60 and γw = 9.81 kN/m³. Find dry density. Use γd = Gγw/(1+e) = (2.70 × 9.81)/(1 + 0.60) = 26.487/1.60 = 16.55 kN/m³. The reasoning is direct substitution; do not confuse void ratio e with porosity n, where n = e/(1+e).

Traps that cost marks

Mixing nominal and design mixes; forgetting unit conversions such as mm to m; using total stress where effective stress is required; choosing the wrong bearing quadrant; and assuming 28-day strength directly from a 7-day result without allowing for the usual strength-gain relationship.