Help! concrete pads atop drain pipe - Drainage, footings

[piper]

I am building a Durabase DIY conservatory which has 4 (450mm cubed) concrete pad footings with a steel base sitting on top of pins on a plate. Unfortunately I have discovered a field drain on the furthest projecting corner (this is hole 'B' in picturetrail link below, of pic no. 1020436, and the sewer is the furthest to the right hole. I have asked durabase, and they admit they are not qualified to answer this type of question. I have clay soil.

http://www.picturetrail.com/sfx/album/view/13290713

So far, I have bought a lintel (in 1020436), and a 19cmx19cm metal plate was supplied by Durabase to spread the load. The photo 'drain pipe 2 options' for concrete pad hole B, the top red x is the original place for the pin to sit on. Can i stick to the original plan, rather than moving all pads over a decimeter (orange x) dig every other hole to the right? The distance from the top of the pipe to the top of the slab is approx 12cm at a guess ('drain profile'), but this is the highest point in the garden. I need to leave 225cm from DPC level for the skirtings. On the concrete pad plan it gives a range of -top of pads to top of steel 250-290mm. (top of steel will be the DPC level).

Also, do you have any advice on when is safe to concrete in winter? (I know i chose the wrong time to do this, hindsight and all that) I have seen many websites about it and suggestions of using warm water, heated aggregates, and 12inch insulation over the concrete. I was thinking to put a disposable barbeque into the hole on top of the gravel, add in the rest after.... With the next few days seeing lows of -9C, I'm not going to bother yet, but when its 0 and -1, perhaps I could try? I am desperate to get some components out of the house, and make use of the annual leave i've taken too....

thanks for any helping the helpless...greatly appreciated

[lutonlagerlout]

4 degrees and rising m8
any lower and you risk total failure
if there is a risk of frost or sub zero temperatures then cover with hessian ,available from builders merchants
LLL

[seanandruby]

I would clear all round the pipe and enough along it to be able to cut the pipe either side of where the padstone will be. This will enable you to incorporate two movement joints, which should be not more than 150ml either side of the beam, padstone, or structure. You can purchase two wrap around flexi collars for this, or two sliding/slip collars. Needs to be 3 degrees and rising with no drop below 4 degrees in 24 hours. and needs covering over whilst curing.

[lutonlagerlout]

whilst surfing the net,i found this mine of useful info
helpful stuff
relating to good practise etc
regards LLL