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value of requiring compaction measurement for footings for light frame construction in good soil? 8

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Engineerataltitude

Structural
Oct 31, 2008
81
In the jurisdiction where I do most of my practice (Sierra Nevada in CA), the soil is really very good for footings for light frame construction. All the preliminary geotechnical investigations I have seen in the past 30+ years have either 2000 or 3000 psf soil bearing allowable for locations where there are no troublesome soil indicators. The local building departments in this area are very reasonable about not requiring geotech reports unless there is some kind of indicator for atypical soil.

With that in mind, is there much or any value to requiring compaction testing for the bottom of footings placed in competent native soil placed at the prescribed embedment depth (either 18" or 24")? Seems like overkill testing to me. My understanding is that if you have excavated into untouched native soil, it is usually compacted adequately for building light frame construction. Correct?

Any benefit to compaction testing I might be missing? I try to be sensitive about not requiring costly inspections if there is limited value to either safety or quality.

btw, I am a civil engineer in practice in this area for the past 30+ yrs. For whatever that's worth.
 
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Every time this comes up I always like to ask:

A: What percentage of the soil along the possible slip surfaces does a compaction test on the soil immediately beneath the footing test?

B: What percentage of the soil in the zone of influence of the footing that will undergo elastic/consolidation/compression settlement does a compaction test on the soil immediately beneath the footing test?

C: What percentage of geotechnical consultancies low bid investigations and make money on compaction testing / footing inspections?

The answer to A: is generally 0% and the answer to B: is generally very close to 0%, and C: is very close to 100%

I suppose it would stop the contractor from doing something absolutely criminally negligent - I tend to think that the battle has already been won or lost during the ground investigation and selection of design parameters.

 
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