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Home > Forums > Structural Engineers > Activities > Structural engineering other technical topics Forum

Cutting hole into existing laydown slab

Read More Threads Like This One

aeroelastic1 (Civil/Environmental)

4 Sep 12 8:16

Hi,

We are putting a steel gate post into an existing 225mm thick cocnrete laydown area. The concrete is reinforced with 10mm long bars (200mm c/c) and 6mm transverse bars (400 c/c). The slab normally carries flask transporters with 15tonne axle load.

A 1.2x1.2m hole will be dugged into the existing slab and the fence post will be cast into a new concrete foundation in the hole.

My question is will the existing concrete laydown slab still be capable of resisting the 15tonne axle load around the cut out hole? What do I need to check?

Regards,

aeroelastic1

Ron (Structural)

4 Sep 12 8:52

Why would wheel loads be that close to a gate post? The hole will be a new "slab edge". If the existing slab edge has the capacity, then the new one will also.

Keep in mind that when you cut a square hole in your slab, cracks will emanate from the corners of the cut.

paddingtongreen (Structural)

4 Sep 12 10:32

Following Ron's note: Best to core the corners and then, for appearance, cut the straights with a saw as much as possible before breaking out the rest.

I don't know what your post is, but why such a big hole? If it is a round post you can drill a little oversize and grout the difference.

Michael.
Timing has a lot to do with the outcome of a rain dance.

dik (Structural)

4 Sep 12 14:53

Can you core a hole for the fence post, drive the post into the soil, and epoxy it in place... 9" slab provides some resistance for the post... else can you core a 12" hole (or whatever) and drill a 12" hole into the soil and fill it with concrete, providing an isolation joint at the slab/post support interface?

Dik

msquared48 (Structural)

4 Sep 12 15:26

I, too agree with Ron here.

If you cut a 48" or so hole in the slab, auger into the grond for the post footing, undercut the slab by say 4" or so for a foot down the augered hole, then backfill with concrete after the post for the gate is installed, you should be fine.

I assume the gate is metal and cantilevered - the reason for the large footing?

Mike McCann
MMC Engineering
http://mmcengineering.tripod.com

aeroelastic1 (Civil/Environmental)

5 Sep 12 8:10

Thanks all for the advice. Yes it's a big cantilever gate with steel post thus the size.

The plan is to dig deeper than the slab and cast the post in with concrete.

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