Planning, Estimation and Management
Planning, Estimation and Management covers project stages, bar charts, CPM/PERT, rate analysis, quantity surveying, tendering and contracts. WBPSC AE questions often use PWD schedule of rates, standard measurement rules and simple network float calculations.
Core rules
- Estimate types: preliminary, plinth area, cubic content, approximate and detailed.
- Rate analysis includes labour, material, plant, overheads, contractor profit and GST.
- CPM: the critical path has zero total float; total float=LS−ES or LF−EF.
- PERT uses three time estimates t_e=(t_o+4t_m+t_p)/6; variance=((t_p−t_o)/6)².
- Measurement: bricks in masonry, concrete in m³ and steel by weight; wastage factors apply.
Worked example
For 1 m³ of M20 nominal mix 1:1.5:3, dry volume=1.54 m³. Cement volume=1.54×1/(1+1.5+3)=0.28 m³. Cement bags=0.28/0.0347≈8.1 bags. Sand=0.42 m³ and coarse aggregate=0.84 m³ before adjustments for bulking and wastage. The 1.54 factor accounts for voids in dry ingredients; it is not a universal code constant.
Traps
- Using wet volume directly for cement content.
- Forgetting GST and overheads in rate analysis.
- Confusing free float with total float.
- Claiming CPM is probabilistic; PERT is the probabilistic network.
- Ignoring wastage and bulking in quantity estimates.