Grade beam with earth form 1

[ldg1945]

Aci 301 was referenced in the specifications.We want the grade beam to be formed with metal or wood forms however the contractor plans to use the earth as a form. By referencing ACI 301 can we make the contractor form the sides of the grade beams.
LDG1945

 

[boffintech]

I guess you mean the following:

ACI-301 2.2.2.3 Do not use earth cuts as forms for vertical or sloping surfaces unless required or permitted by Contract Documents.

As long as you have 3" of cover for the rebar in the grade beam why do you care if the contractor uses earth for the forms? The contractor is responsible for means and methods so why are you getting into the actual construction?

As an alternative, you could visit the job for an pre-pour inspection and measure the cover down to the nearest 1/8" and make him "wish" he had used metal or wood forms.

 

[SlideRuleEra]

ldg1945 - Since your question is can you "require" forms based on ACI 301, I would say yes.

However if you "choose" to waive the requirement for forms, a compomise could be to use ACI SP-4, Formwork for Concrete, as the authority. On many jobs we allowed an ADDITIONAL three inches of concrete rebar cover (for a total rebar cover of say 5 or 6 inches) to be substituted for forms.

Here is a link for general information

http://www.concreteconstruction.net/pclinic/pc_template.asp?ProbClinicID=C910838A

http://www.SlideRuleEra.net

 

[archeng59]

my specs require formed sides for grade beams, but not footings. contractors frequently request approval to use earth forms to save $$, but I seldom approve the request. Usually, they bid the wood/metal forms and ask to use earth forming so they can increase their profit margin. in my area, the soil typically is not cohesive enough to prevent sloughing of the sides of the excavation during rebar placement. the sides of the grade beams are not truly vertical and the grade beam typically has the top much wider than the bottom. the grade beam then acts as a combination footing and beam spanning between piers. the sides of the grade beam bear slightly on the soil, which is why I say it acts partially as a footing. If your soils are not expansive, as they are in my part of the world, that likely isn't a problem and you won't have to worry about uplift. for footings, I really don't care if the sides are earth formed since everything bears directly on the soil. earth forming usually isn't as "exact" as when wood or metal forms are used.

 

[henri2]

If your specs required wood forms and the contractor used metal forms instead with asking you for permission, would this be a problem?

 

[archeng59]

in my opinion, metal or fiberglass forms are acceptable unless the concrete is exposed architectural concrete, when you might need to be concerned with color uniformity. elevated structural slabs & beams are often cast using metal pan forms, so metal forms are acceptable and can be reused more often than wood forms.

 

[boffintech]

Being a construction inspector I have decided to make it a practice to see if specs reference ACI-301. Sure enough I have been to 3 big jobs this week, each spec referenced ACI-301, and each superintendent had no idea (or claimed to have no idea) that that “earth cuts as forms” line was in there.

ACI-301 2.2.2.3 Do not use earth cuts as forms for vertical or sloping surfaces unless required or permitted by Contract Documents.

On one job the specs read that “Formwork shall comply with ACI-301 Chapter 2.” It seems to me that specs don’t get any more clear or specific than that. The contractor wanted to pour a foundation for a cooling tower consisting of 4 spread footings connected by 4 tie beams of which all were in earth cuts. This footing rested in residual soils suitable for support of the design load of 3000psf (which I verified with a hand auger and a DCP on the previous date) and only minor sloughing of the excavation sides was evident. Some soil fall-in material had to be removed, but this was just material kicked in by the rod-busters and the carpenters during placement of the rebar and the templates for dowels, respectively. I wrote up an inspection report that referenced the specs and the relevant line in ACI-301 and noted that the proposed concrete placement did not comply with the contract documents. The concrete placement was held up for an entire DAY while the contractor sorted this out with the EOR. Apparently neither the contractor not the EOR was happy with my mastery of ACI minutia.

I knew the contractor was upset with me and I sensed that he wanted me leave his office-trailer. I got this feeling because he gave me a little hint, a clue, a sort of suggestion; he said, “Get out of my trailer.” I said look I don’t write the specs, I just write reports that note discrepancies between the specs and the work, that’s all. So he was OK after that, but still not very happy.

 

[AggieYank]

For typical slab on grade beams, we use earth cuts all the time with no problems at all. Just make sure that there isn't a lot of loose soil in the beam soffits, and if there is, have them clean it out.

 

[BigH]

In UK, from what I understand, they use excavation side slopes quite extensively as formwork. You can see Tomlinson's book "Foundation Design and Construction". The only thing is that with casting against the earth excavation walls, you will likely use a bit more concrete - but this would be offset by the savings in labour and forming materials.