Non correct Excavation

[hoshang]

Hi everybody

During the excavation for a mat foundation, we encountered a wrong excavation elevation by the surveyer for approximately 50% of the area. So, we recommended the contractor to continue the excavation with correct elevation until we solve the extra excavated area. The elevation difference is about 2.15m. Please any help.

 

[hoshang]

Hi

I forgot to include these:

1- should we fill the extra excavated area (about 2.5m) and then lay the mat.
2- should we design columns (of height 2.5m) under the mat in the area of the wrong elevation
or other options

 

[dhengr]

“other options....” It seems to me that this foundation design and excavation project could benefit significantly by having some local, and real, engineering experience and judgement applied to it. If you find yourself in trouble while digging yourself into a hole, the first thing you should do is stop digging.

 

[ztengguy]

I would fill the hole with fill, or clsm

 

[hoshang]

Hi

Is the filling the best solution?

 

[hokie66]

We cannot possibly solve your problem without knowing more about your site and your structure. Why does the building have a mat foundation? There is a likelihood that a mat foundation sited on two different materials, native soil at one end and fill at the other, will experience differential movement problems. Agree with dhengr...the decision is not simple, and needs evaluation by competent geotechnical and structural engineers.

 

[EngineeringEric]

Are you thinking that the design and construction of many short concrete columns and footings and redesigning of the mat is easier than laying down a bunch of compacted fill? I think dhengr provides the best advice on this one... sorry

 

[hoshang]

Hi

I wonder if there are other solutions.

 

[CANPRO]

How big is this mat foundation? To take care of the different support conditions you could always excavate the remaining area down to the "wrong" elevation then bring the entire area back up to the "right" elevation with compact structural fill.

I do agree with others, your best course of action is probably to find a local experienced engineer to help with the most economical solution. Since this is the surveyors/contractors mistake you could also put the burden of solving the problem on them, with the solution to be approved by you or another engineer.

 

[msquared48]

Option #10: Dig the rest of the mat down to the incorrect elevation and pour a super thick mat.

Mike McCann
MMC Engineering

 

[oldestguy]

A common problem with "over excavation" is that it gets filled in improperly and structure settlement results. Generally that filling in is done by those on the job, sometimes trying to hide their mistake. Then the question of "why" takes time and expense. I sense a "can of worms" there.

 

[cvg]

2.15 meters is a lot. I would seriously consider replacing the contractor at this point.
columns are just a silly idea, you need to backfill
that fill could be in order of cost and suitability to handle heavy loads
a) structural concrete
b) lean concrete
c) very well compacted aggregate base course
d) and last but worst would be compacted native material

 

[hanihafiz]

The solution depends on over-excavation geometry and soil nature. In a case we got irregular over-excavation in hard rock. We used back fill 24 MPa concrete to reshape to the original foundation level.