Differing site conditions: when the ground is not what the documents show
At 10:20 the superintendent sends photos: the excavator has hit a concrete wall and slab 1.4 m down at the north-east corner of a new brewery. Nothing on the drawings or in the geotechnical report shows a structure there. The operator wants to break it out and keep the trucks moving.
Stop disturbing it, record it against what the contract documents show, and give written notice before anyone breaks it out or covers it; keep working elsewhere meanwhile. The owner needs evidence to assess the find, and hauling the concrete away removes that evidence. The US federal clause, for one, covers hidden physical conditions that differ materially from those the contract indicates, and unknown ones of an unusual nature that differ materially from conditions ordinarily encountered in that work; it requires written notice promptly and before they are disturbed.
- Stop that spot and make it safe, and move the crew to other work, as in deciding with incomplete information.
- Record it where it lies: photos with a rod for scale and a fixed point in frame, depth and extent from gridlines, and a sketch.
- Set it beside the documents — drawings, geotechnical report, borehole logs — and note exactly how it differs.
- Send written notice the same day to the person the contract names: the facts, how they differ from the documents, the work affected, and that you consider it a differing site condition. Ask for an inspection and a written instruction.
- Track it as a change from the first hour: its own cost code, daily crew, equipment and standby records, and its effect on the schedule.
Common mistakes
- Breaking it out to keep the trucks moving before anyone else has seen it.
- Waiting for the engineer's visit before putting anything in writing.
- Booking the removal to the excavation cost code.
Checklist
When the ground surprises you
- That spot stopped, the rest still working
- Photos with scale; depth, extent and a sketch
- Documents compared, difference written down
- Written notice today, before it is disturbed
- The owner's instruction in writing
- Its own cost code from hour one
Check your understanding
The geotechnical report is marked "for information only" and is not a contract document. Your excavation finds wet sand where its logs show clay. Do you still give notice?
