Construction Methods, Marine Equipment and Project Management
Marine construction questions test plant selection, method sequencing, measurement rules, and the contractual management of weather and ground risk.
Marine plant and methods
- Piling runs from jack-up platforms or floating barges with templates; vibratory hammers for sheet piles, hydraulic impact hammers for bearing piles, with set criteria from dynamic testing or restrike.
- Concrete underwater is placed by tremie from the bottom up with the pipe kept embedded; never free-fall concrete through water.
- Caissons and cofferdams need sinking and ballasting control, sealing checks, and a dewatering check against uplift.
- Rock and armour placement uses fallpipe vessels for accuracy and side-dump for bulk; positioning by DGPS with tolerance stated per layer.
Measurement and payment
- Dredging may be measured in situ by before-and-after survey, in the hopper, or in barges; each yields a different number because of bulking and overflow losses, so read the specification before pricing.
- Reclamation fill is often paid on placed compacted volume; subsoil settlement risk usually sits with the employer, construction tolerances with the contractor.
Programme and cost control
- Critical path and float: weather downtime belongs in the programme as a probabilistic allowance, not as a fixed line item added at the end.
- Earned value: CPI = EV/AC and SPI = EV/PV; a CPI below 1 means each unit of work costs more than planned.
- Risk allocation: ground conditions, wave climate and permitting delays are the classic dispute areas on marine contracts.
Worked example
A piling package: planned value PV = 1,000 units, earned value EV = 800, actual cost AC = 900. CPI = 800/900 = 0.89, so work costs 12% more per unit than planned. SPI = 800/1,000 = 0.80, so 20% of planned work is not yet done. Forecast cost at completion = BAC/CPI = 1,000/0.89 ≈ 1,124 units - valid only if the variance is systemic rather than a one-off, which is the judgement the question expects you to state.
Traps
- Comparing dredging volumes measured on different bases without conversion factors.
- Programming zero weather downtime and claiming it later as a variation.
- Quoting CPI and SPI without stating the baseline or whether the variance is typical.