Bell shaped holes?

[demuire]

Hi all,

I'm digging the holes for my carport at the moment, and according to the plans from Titan the holes are supposed to be bell shaped:



What's the best way to make them bell shaped? The holes are 300x600, and according to the drawing the bell should be 150x200 (which would make the bottom of the hole 600mm wide, although that doesn't really fit the scale of the drawing, maybe the drawing is referring to a deeper hole). I've just used the post hole digger to chip away the insides at the bottom, but it's slow going and difficult to make the bell that wide...

Also, one of my holes has hit the storm water pipe:



I'm guessing I'll have to re-route the storm water, what's the best way to do this? Chip away the sides until I get clear access to the pipe and then cut and put in 4 x 45 degree bends in it to get it further away or something? Or should I just dig the hole wider to get better access? If I do this, how do I "define" the hole again? Re-fill and reshape the hole? The pipe is about 300mm underground, so about half way down the hole. I've also got to tap into this pipe to pipe the gutters from the carport into it... Is that just a case of putting a T-piece on the pipe?

Lastly, do I need to cover or mark the holes to prevent anyone from falling in? It's in my front yard (away from the street, but still in my front yard...)

Thanks!

[Bleedin Thumb]

OK now I may get flamed for this advise but no one has respondes so....

Those type of details are usually taken with a grain of salt, IE you make an effort to comply but if it is impossible to comply (meaning the architect/engineer lives on another planet) you do the best you can do.

I usually use a crow bar to bell out the hole then get in there with your arm to take out the spoil.
Unless it was specified because you have very sandy soil - doesnt look it - as long as you dont have smooth sided holes I wouldn't panick.

AFA the stormwater pipe goes.... if it was me...I would leave it.... but that is the sort of person I am.

Its right on the edge - it wont effect the footing and if you have a problem in the future its easy to redirect them...but if it worries you now..go for it.

[demuire]

Thanks for the reply. I have to get the holes inspected by the council before I can proceed to put the car port up, not sure if they'd approve it with the storm water pipe there?

[Bleedin Thumb]

Ah...in that case it may be better to redirect it now because they are sure to pull you up.
Stuff something - rags, thick paper etc in the hole while you're working ..it saves cleaning out the hole again,


Obviously you would use a qualified plumber to do this work so there would be no need to make sure that the pipe is backfilled and cant be seen or mentioned to the inspector

[journeyman Mick]

It was pretty common practice to "bell" post footings in the past, but rarely specified now. Basically, as BT said, you do the best you can. That drain pipe is going to be a nightmare if you dig to it from the bottom of the existing hole. If you open up the existing hole you'll make a huge hole that you'll need to fill with concrete. More concrete = more $$. If possible I'd dig a new "U" shaped trench around the footing that intercepts the pipe either side. Cut the pipe and reroute then just smash the pipe in the bottom of the hole.

Mick

[demuire]

Hmm... Can I just make the hole bigger, re-route the pipe and then fill the "extra" section back up so that I still have just a "normal" hole? Also, with plumbing the gutter to the storm water, can I use a T-section, or would I need a Y-section to "keep the flow" (???). Or perhaps it would be easier to plumb it to a gravel pit and leave the storm water pipe by itself...?

[journeyman Mick]

Hmm... Can I just make the hole bigger, re-route the pipe and then fill the "extra" section back up so that I still have just a "normal" hole?..............

You can if you properly compact the soil, preferably with some type of mechanical compaction device (wacker packer, sheepsfoot trench roller, plate vibrator). But this would be more trouble than digging the "U" shaped trench, which you'll have to any way for the pipe to run in.

You should cover the holes up with ply or erect a barrier to prevent someone from falling in. In this litigious day and age you can be sued for someone else's stupidity/your negligence.

Mick

[ian]

can you move the car port 6 inches?
If so refill all the holes and redig them in the new locations
don't tell the council inspector

ian

[joe greiner]

The belled bottom is merely to provide sufficient bearing area on the soil. The taper is the minimum (with respect to horizontal) allowable for shear transfer within the shaft, while minimising the amount of concrete for cost. Although it'd require more concrete, the taper can run all the way to the top if it's easier to excavate that way. Council and engineer should have no quarrel with that.

Joe

[falcon]

I take it that the holes are to support the posts for the carport? Or are they a pier hole as part of foundation for the slab. If the later , you could fill in the hole and move it in a bit. (the easy way)

If it is for the post, how deep down is the pipe. What you'll have to remember is that you'll need a big hole to get good access to get in there and redirct it. Not sure how you'd go trying to pack in soil again to have a decent hole for concrete.


Its only storm water , so cant see why you couldnt poor concrete over it. (no expert on the matter tho, but worth a call to inspectors to discuss)

[joe greiner]

In my humble (but professional) opinion, that's not a perfect detail for the junction of the slab with the post footing. Better for the slab to be isolated, e.g. footing top flush with the top of the slab and cushioning between them. The detail legend (if I read it correctly) indicates this is "Option 2." How does "Option 1" accommodate the post? Or are these plans really, really, really generic?

Joe

[journeyman Mick]

The belled bottom is merely to provide sufficient bearing area on the soil..........

Joe,
I had always assumed that the bell was there to increase the hold down capability of the footing, but then I live in cyclone country. If it's not to increase the hold down capacity I'd be inclined to just dig the hole the same size all the way down and use a bit more concrete.

Mick

[demuire]

Hmm, okay will see if I can put something on the holes so people don't fall in. Or maybe put some cones around the hole and hope no one pinches them. Hopefully no one decides to fall in while I'm at work today

ian: Would prefer not to move the carport as it would mean it wouldn't line up with the house...

From what I'm reading I'm guessing the bell height doesn't matter, but the bottom should be the width specified (in this case 600mm)?

falcon: It's for posts. The pipe is about 300mm underground...

joe: I think the plans are very very generic...

[Barry_White]

With all my experience of selling and building sheds and carports belled holes in a non cyclonic area is overkill. As Demuire says the plans are probably generic and because they probably build all the time in cyclone areas they are just covering themselves. The belled hole as Mick says is to hold the carport down in the wind not support the weight as this is minimal compared to the wind uplift.

If you are pouring a concrete slab over the footings later there is no way it would blow away and pull the posts out of the ground. There would be more chance of the wind ripping the tin roof off but would leave the posts in the ground.

I don't think the council should mind if the concrete was poured around the stormwater. If it was sewerage that might be different.

[Outbackrr]

I agree with Mick that the 'belling' is to provide uplift resistance by acting as a soil anchor. Titan must have an old engineer or footing design, as there are no mechanical means of digging bell-shaped holes.

The concrete volume of a straight-walled footing would have to be increased to compensate, with weight, for the uplift resistance provided by the original design.