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Related Articles


Subgrade Inspection, and backfill

Subgrade Inspection, and backfill

Subgrade Inspection, and backfill

Material Earth-Fill Widen roads for bike lanes
Purpose: Length of trench 23 Metres
depth 2.5 metres
depth of bench 0.6 metres
width of trench 4.5 metres

Recent engineering graduate working as field inspector/quality control

Is settling and cracking, the governing failure mode for roadway filling? How come we only consider, Dry Density and optimal moisture content for compaction, and not other engineering properties such as shear strength.

What happens if the foreman adds another lift when the previous lift fails, how detrimental is this for 5-6 lifts are going to be added?

RE: Subgrade Inspection, and backfill

There is no way for us to clearly give you advice unless you preface your question with a statement as to exactly what this job is. Is this some large culvert for super highway with rigid specifications for compaction or is this water line under a driveway to a residence? What is your position, project engineer? contractor's superintendent? How deep is the trench and what is the soil type? The more detail that you can present, the better the results here. You are free to edit your post at any time.

RE: Subgrade Inspection, and backfill

benching is used for trench safety and also frequently used for embankments to provide better compaction along the edge. Soil cut from benches can be used for fill if it is suitable for use as fill material. Suitability should be defined in the specs. It would also need to be properly moisture conditioned. Top-soil would generally not be considered suitable. I would have thought that for filling a ditch, you would have stripped out the top layer of existing organic/silty material in the ditch which is unlikely to be suitable for embankment.

first lift has a much lower Dry Density value, compared to 2nd and 3rd lift - you will need to maintain the required percent compaction regardless of the type of material being placed.

what are the effects if another lift is added before the previous one has passed - you had better hope it passes, otherwise you may have to go back, remove it and re-compact it.

RE: Subgrade Inspection, and backfill

the contractor has an obligation to deliver all compacted fill to specification. Even the first lift!

soil derived from the bench excavation must meet spec when reused for earth fill. That's also the contractor's responsibility.

Hopefully the engineer defined the material requirements.


ípapß gordo ainÆt no madre flaca!

RE: Subgrade Inspection, and backfill

If you are backfilling over soft soils, the engineer may allow overexcavation to a reasonable depth and graduated compaction to your first left. Don't forget about that RFI!

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