The Compressed Cure That Broke the Critical Path
A 14-month wastewater pump station upgrade must finish before a regulatory deadline that cannot move. The baseline critical path runs through: site mobilization (10 d) → deep excavation (30 d) → precast wet well delivery (procurement lead 60 d, can start after design freeze) → wet well installation (20 d) → mechanical fit-out (25 d) → commissioning (15 d). The client directs the team to compress the schedule by 45 days without adding cost. The planner proposes crashing excavation by 15 days (adding a second crew, +$180k), overlapping installation and fit-out by 10 days, and reducing commissioning by 5 days. During review, the superintendent notes the wet well cannot be set until excavation is complete and dewatered, and commissioning cannot begin until the electrical utility energizes the site-a 30-day utility process that currently starts only after fit-out.
1. Evaluate the proposed compression plan. Which actions actually shorten the project duration, and what is the correct way to recover the 45 days?
Read the worked answer
Test each action against the driving path, not against individual activities.
Excavation crash (−15 d): Excavation is on the critical path, so crashing it shortens the path only if the downstream successor (wet well installation) can start earlier. But wet well installation also requires the precast unit on site. If the 60-day procurement finishes later than the crashed excavation, the crash buys nothing-the path floats to procurement. Check the procurement finish date first. If procurement is the true constraint, crashing excavation is wasted money.
Installation/fit-out overlap (−10 d): Only valid if the work is genuinely separable. The superintendent states the wet well must be set and dewatered before fit-out-so a full overlap is not physically possible. A partial overlap (fit-out starting in completed zones) may be defensible; a blanket 10 days is not.
Commissioning reduction (−5 d): Check whether commissioning is truly on the driving path. If the 30-day utility energization starts only after fit-out, then energization is a hidden critical path parallel to commissioning. Cutting commissioning 5 days while energization still runs 30 days after fit-out yields zero schedule benefit.
Correct recovery strategy: Re-sequence the utility energization to start during fit-out (or earlier, after the electrical room is dry and secure), pulling the 30-day process off the tail of the schedule. That single logic change can recover up to 30 days at near-zero cost. Then attack the true longest remaining path-likely procurement, by expediting the precast delivery or releasing the design freeze earlier. Only crash excavation if, after the logic fix, excavation is confirmed driving. Lesson: compress the driving path, verify physical/logic constraints, and look for hidden parallel critical paths (permits, utilities, procurement) before spending money on crashing.
2. The client insists the 45-day recovery be shown as achievable in a revised schedule. What validation steps must the planner perform before submitting it?
Read the worked answer
Before submitting, the planner must prove the revised schedule is logic-valid and resource-feasible:
- Re-run the critical path after the logic changes and confirm the new driving path and total float. A recovery that doesn't move the critical path is fiction.
- Confirm all constraints are honored: the wet well cannot precede dewatered excavation; commissioning cannot precede energization. Any overlap must be justified by a defensible start-to-start relationship with lag, not an arbitrary date constraint.
- Check procurement and permit lead times against the new dates-expediting a 60-day precast lead is a real commitment, not a schedule edit. Get vendor confirmation.
- Resource-load the crashed activities: a second excavation crew needs space, equipment, and dewatering capacity. Verify the resource histogram doesn't create a new constraint.
- Remove or justify any hard constraints / date constraints that mask true float; a schedule held together by constraints will not survive execution.
- Identify the new near-critical paths (float ≤ 5–10 days) so the team knows where risk now lives.
Only after these checks should the revised schedule be issued-with the assumptions (expedited procurement, re-sequenced utility) documented as schedule basis.