Nov 02, 2012 3:52 pm
I am building on a property where the engineer designed the footing to be of pier and beam design with the pier being about 2m deep. The soil report actually recommended the use of screw steel piles because water was found in particular one of the bore hole where it came in quickly (the other two water came in slowly).
After quite a bit of reading, I do prefer concrete piers over steel screw piles as the foundation method but it seems there might be some problems when trying to put them in due to bore holes possibly collapsing. A couple of builders I talked to are saying that screw piles will be the way to go but it seems like they say that because it's the easier for them. Ont he other hand, I asked the engineer again and he still thinks that concrete pier is the way to go. This includes my uncle who is also a structural engineer. I called up foundation companies and they prefer concrete piers also.
What would people do in this case? I have to put in about 40 piers of 400m thickness. I got a few quotes done and going concrete piers would be around $8-10K while steel screw piles will range from 11k to 15k (because they have to go down to 5m based on experience within the area of this piling company).
The soil profile is something like this:
0 < 1m : Brown and Grey silt clay sand FILL (loose)
1m < 2m Dark Grey black silty sand (loose)
> 2m: Light Grey brown sandy clay (medium density to stiff - very stiff)
Re: concrete piers or screw steel piles?2
Nov 02, 2012 4:30 pm
Sounds very similar to what my designer has planned for our new place - 65 piers, 450dia x 2000 min piers. Concrete all the way!
Your builder recommends it, you ‘resident’ structural engineer recommends it, you prefer it after your own research - it's a no brainer – concrete.
There are a couple of ways around collapsing holes, the crew that install the piers will take care of it. There was a good example of how it’s done last week on Grand Designs Australia.
Re: concrete piers or screw steel piles?4
Nov 02, 2012 11:01 pm
Do a search for Grand Designs Australia S03E02 and you may find something of interest....
Abut 9 minutes in for a minute or two.
They use a continuous flight auger piling machine.
Re: concrete piers or screw steel piles?6
Nov 03, 2012 7:32 am
No casing required for this process. The auger drills down into the ground, removes most of the dirt as it goes. Any that falls back in on the screw is dragged out when the auger is pulled up. As it's being raised, concrete is pumped (through the hollow tip of the auger) into the base of the hole filling the space immediately made available below the tip of the auger. Once the auger is out a steel reo cage is pushed down into the wet concrete.
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