Wet sloppy base to concrete pier/pad footings

[Amb]

Hi everybody. This is my first post, though I've been reading for quite some time. I'm just about to pour the concrete footings for my 7x12 m colourbond shed. The 12 holes are about 450mm diameter and 700 mm deep. The holes where dug a couple of weeks ago, and we've had a lot of rain since then. I kept emptying the holes out, but inevitably the bottom of the holes, which was once solid heavy clay, has become soft and sloppy. If I poke a stick into the sloppy bottom, the clay becomes hard about 200-300 mm in. It will be almost impossible to clean out that very sloppy clay, and if I do, the holes will end up being 900-1000 mm deep! I know the base of the hole should be clean and solid, but will it make difference for a simple lightweight colourbond shed? I am guessing that pouring the concrete on top, the sloppy clay will have no where to go, and should be able to support the weight of the concrete until the sloppy clay dries out. I can put up with some settlement and movement (so can the steel shed), but maybe I'm heading for disaster with large amounts of settlement? Thanks for any help. Amb

[thebuildingsurv]

why dont you dig it out the morning your concrete arrives. You may get a bit of movement. One option could be to get a dry bag of concrete or even just cement nd ram it in to the base of the hole.

[Tommy]

The trouble with clay is it is a very reactive soil.What you should do is just get a bob cat in with a 450 auger and dig the piers out until you have stable soil.He will be lucky to be there for an hour and should only charge you about $80.00.The extra concrete would be only about a half a cubic meter and is only about $100.00..So for $180.00 is a small price to pay when it comes to footings and piece of mind..

[Amb]

Thanks for both your advice. Tommy, good idea, but I will still have to get the slop out by hand, too sloppy for the auger. I cleaned out one hole, and found the clay is stiff enough 100 mm or so below the slop. I could auger forever looking for just right clay, the deeper you go, the clay just gets a little bit stiffer, but still not good and stiff. I think the best I can do is scrape out the bottom a bit, and then as buildingsurv suggested mix in half a bag cement or so. Will be pouring on monday, nice weather then, am open to suggestions until then. I'm going down to the 'junk' shop now to find a good old saucepan with a strong handle - I reckon that will be good for scrapping out the bottom.

[MrFixIt]

Hi

If is really is THAT sloppy, what I would do is to get some 20mm bluemetal, mix the blue metal with dry cement and put his in the bottom of the hole.

Ram the bluemetal/cement mix INTO the clay/slop and use it as the "wet" portion of the "concrete" mix. Use a relatively small size ram eg 75mm square, or even use the shovel.

The nett result should be a brown but firm and rock hard when set, concrete base. This will provide a stable base on which to pour your footings.

BTW a 700mmx450mm lump of concrete is hard to move :D

[Amb]

Thanks mrfixit and others. The advice from the 3 of you helped me decide what to do. Today I emptied out any water but didn't remove any of the sloppy clay. Then i dry mixed about 1/2 bag cement with 1/3 barrow of a coarse gravel/crushed rock mix I've got lying around. Put most of that in the bottom of a hole and worked it in well with the sloppy clay. Then I got in the hole and worked it really well with my heels, all the time adding a bit more from barrow until it was not sticking to my boots and became very well compacted. It took about 15 minutes a hole, and I'm very happy with the result. Formed a very sound base that will set like concrete. Well maybe not quite that hard, but it would have be harder than the existing clay, even in summer. It also means I won't have to order as much concrete. A small minimixer will do it, which will be able to get in close to the holes, so no barrowing! Thanks again. http://www.woodworkforums.ubeaut.com.au/images/smilies/actions/2thumbsup.gif :2tsup:

[Amb]

Thanks mrfixit and others. The advice from the 3 of you helped me decide what to do. Yesterday I emptied out any water but didn't remove any of the sloppy clay. Then i dry mixed about 1/2 bag cement with 1/3 barrow of a coarse gravel/crushed rock mix I've got lying around. Put most of that in the bottom of a hole and worked it in well with the sloppy clay. Then I got in the hole and worked it really well with my heels, all the time adding a bit more from barrow until it was not sticking to my boots and became very well compacted. It took about 15 minutes a hole, and I'm very happy with the result. Formed a very sound base that will set like concrete. Well maybe not quite that hard, but it would have be harder than the existing clay, even in summer. It also means I won't have to order as much concrete. A small minimixer will do it, which will be able to get in close to the holes, so no barrowing! Thanks again. http://www.woodworkforums.ubeaut.com.au/images/smilies/actions/2thumbsup.gif :2tsup:

[Amb]

Thanks mrfixit and others. The advice from the 3 of you helped me decide what to do. Yesterday I emptied out any water but didn't remove any of the sloppy clay. Then i dry mixed about 1/2 bag cement with 1/3 barrow of a coarse gravel/crushed rock mix I've got laying around. Put most of that in the bottom of a hole and worked it in well with the sloppy clay. Then I got in the hole and worked it really well with my heels, all the time adding a bit more from the barrow until it was not sticking to my boots and became very well compacted. All up it took about 15 minutes a hole, and I'm very happy with the result. Formed a very sound base that will set like concrete. Well maybe not quite that hard, but it would have be harder than the existing clay, even in summer. It also means I won't have to order as much premix. A small mini mixer will do it, which will be able to get in close to the holes, so no more barrowing! Thanks again.