Footings in backfill

[gsouth]

All,

We had an excavation for a swimming pool completed which has caused a small issue with the planned deck.
While excavating a small septic tank was discovered (no longer used) which was right on the edge of the pool. This subsequently collapsed into the pool, leaving an area behind it which has been backfilled......

This area we have to put the post for the deck (Small walkway about 1300 wide and only 600mm off the ground.

What advice do you have for putting footings into this type of soil.. ?
The filled area can't 'slip' as it's surrounded by the original soil and the pool wall - it may 'sattle' over time, however great care was taken in filling this hole to ensure it's as compacted as its going to get....

Cheers
Geoff

I have tried to attach a pic - my first attempt to do so.




file:///C:/DOCUME%7E1/ADMINI%7E1/LOCALS%7E1/Temp/moz-screenshot.jpg17510

[silentC]

An engineer would probably tell you to dig a pier hole through the fill to the natural ground beneath. That might be overkill for your application. Can you go up a size on your bearers to span that area?

[bitingmidge]

I'm not an engineer, but dig through to natural ground.

You don't have to make the post that long, and you can even use a lighter concrete mix, but dig into natural ground.

Cheers,

P

[gsouth]

Thanks for the replies
Natural ground is about 2 metres down.....

Geoff

[silentC]

Better get a long shovel then!!

If you want to do it by the book, then that's what they'll tell you to do. Otherwise your only option is to find a way of not having a post there, perhaps by spanning it with a heavier bearer or cantilevering from another post.

Or you can throw the book away ;)

[rod1949]

Another option is to spread the footing over a larger area ie. instead of digging say a 300mm x 300mm hole to a great depth, make the hole say 600mm x 600mm this way the load is being spread over a larger area and the depth can be a lot shallower (say 600mm deep). You will need at least a 100mm of concrete under the bottom of the post/base plate.

[bitingmidge]

If you want to do it by the book, then that's what they'll tell you to do. Otherwise your only option is to find a way of not having a post there, perhaps by spanning it with a heavier bearer or cantilevering from another post.

You've got to wonder what they were thinking when they wrote the book eh??
;)
Yet another option would be to dig out the fill and compact it properly in small layers.

Yep, you could put a bigger footing on, but if the soil hasn't been compacted evenly, you'll get the post sinking on an angle!

Or you could just pack up the bearer in a year or two after it's all settled.

cheers,

P

[silentC]

You've got to wonder what they were thinking when they wrote the book eh??
They're just a bunch of nazis spoiling all our fun :p

[Tools]

Use a duragal stump with adjustable head,then adjust if and when settlement occurs.

Tools

[Dan_574]

heres a bit of an overkill for your job but have a look at the site below, a mate of mine does this and I ve worked with him, theres things are great. They screw them in with an excavator for just the thing we are talking about, they can also be left out of the ground as a conventional post.

http://www.steelfoundations.com.au/home.aspx

[ozwinner]

Or you can throw the book away ;)

Dont throw the book away, use it as a pad at the bottom of your posthole.
Surely all them regs must be able to hold up a piddly little post.

Al :D