Clay foul sewer under drive. - Depth of cover over a clay pipe under a

[ger]

My drive currently consists of concrete slabs 900x600 and probably was laid when the house was built in 1964 [the slabs are well weathered]. There is a slope in the drive up from the pavement [700mm over 6 meters]. There is a main clay foul sewer pipe which runs across under the drive and garden, this pipe serves my house and other houses as it goes under their gardens and drives.
I now want to block pave the drive and some of the garden to take two cars side by side. I would like to flatten the slope as much as possible which would involve digging out the area where the pipe runs under. The pipe is approximately 400mm under the drive [top of concrete slab to top of clay pipe 400mm].
The question is how much can i reduce the cover over the pipe or is the 400m the limit. Perhaps some form of concrete cover to protect the pipe any suggestions. Ger.

[GB_Groundworks]

to handle the weight i'd be tempted to encase the whole pipe in concrete, not just on the top but at the sides and bottom as well to pass the load around the pipe not onto it. i'd also protect the pipe aswell before concrete with some kingspan or the like.

flowjoe will be able to tell you the exact cover required.

[lutonlagerlout]

the pipe should be concreted in already,but if you expose it and encase with 100mm of concrete all round ,then lay your 125mm of type 1 over that you should be ok,dont forget the pipe will be falling so may be higher at one end
cheers LLL

[GB_Groundworks]

as a side note heard of another groundworker round here who on pouring a footing for a conservatory shot the concrete straight out the wagon onto a 4 inch clay pipe, broke the pipe and put almost 2 cube down the sewer. they left it and was a road up job etc got right into the main sewer expensive fix.

[Dave_L]

Holy crap! That doesn't even bear thinking about.

[seanandruby]

should be 100/150 ml concrete cover all round at that depth, also fibreboard movement joints at every coller.

[ger]

Many thanks for all the replies. I shall check to see if the pipe has some concrete around it and take it from there. Ger

[Tony McC]

This is what you need.

[ger]

Thanks that explains everything. Ger.