Foundations - bridging a drain run

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Hello,

I'm in the process of replacign all of the old clay foul and surface water drains at the rear of our house with new plastic pipes for our new rear extension. As we are head of the run, the drain pipes are quite high and close the the ground surface. As a result they will be intersecting the foundations quite high up. My question is:

Can I shutter the trench from top to bottom and essentially pour the concrete on either side, filling the hole with pea shingle and using lintels over the top OR is there a maximum depth of pea shingle allowed below the pipe and do I have to carry the concrete up to a certain depth below the drain pipe to bridge the two side?

If I don't need to bridge the concrete below the pipes, I suppose I could leave a step in the existing ground below the drain pipe up to 100mm below the pipe and fill that with pea shingle?

Any advice will be much appreciated.
 
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I recently had to build over a sewer at both ends of my foundations, with the sewer decreasing in depth from one end to the other.

At the shallower end I left the soil in place to the same width of the sewer. I then placed decent paving slabs agaist the soil walls on both sides, then used 3" x 2" timber to brace against them and then lent ply against the timbers. At ground level, I put a bit more timber between the 3" x 2"'s so that they couldnt move. This provided a strong brace for the concrete to be poured on each side.

Once dry I removed the timbers and then the ply. Then bridged over the sewer with lintels and built up from that.

Filled up the void with pea gravel, left the paving slabs in place

Worked very well
 
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All of the suggestions are workable.

However, if the pipe is close to the surface of the trench concrete then many bco's will accept the pipe wrapped in compressible material, i.e. fibreglass insulation.
 
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Yes this is relatively simple!
stop concrete short at each side of pipe, best about o/d od pipework +100 - 150 each side for gravel protection, standard concrete lintel width of opening + 150mm bearing each side, so for 110 diameter pipe lintel size should be circa 700mm.
If the top of pipe is that shallow that the lintel will be exposed when finished levels you may need to consider a steel lintel, you could have a 100mm box section with a 10mm plate wlded to the bottom that would project to bridge cavity and give bearing for external face. steel would have to possibly be galved or painted with bitumastic to BCO recommendation.
Russell
 

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