Replacing stones in driveway after drainage installation

I have removed about 1 metre wide of "crazy paving", on a driveway, to install a drainage pipe under it. As the regulations say, I placed 50mm thick (900mm wide) concrete slabs over the pipe spanning the trench. I have allowed for a 30mm gap between the top of the slabs and the underside of the paving stones. The latter are made from broken concrete 50mm slabs. The existing paving is resting on a thin layer of 10mm gravel which in turn is resting on tarmac about 120m thick. The paving has mortar on the joints, fairly wide in places.
My question is, in order to replace the paving stones I removed, which is the best technique I can use in my situation to fix them so that they will not rock or sink with the weight of the cars?
Here is a picture of the driveway (if it works)
Thanks in advance
[URL=http://imageshack.us ]
http://img341.imageshack.us/img341/2176 / drivewaycrazypavingxi9.jpg [/URL]
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No I think the picture link did not work, I'll try again:
http://img341.imageshack.us/img341/2176/drivewaycrazypavingxi9.jpg
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On Sat, 12 May 2007 05:23:25 -0700, peternoon wrote:

Looking at the picture, I'm wondering two things. How wide is the trench for the waste pipe and what is the external diameter of the pipe?
For all one can see, the 900mm flags might just be resting on 25mm of soil on each side and the trench might be 850mm wide. Depending on the width of the trench (if it's, say, 300mm or less) it might now be safe just to replace the gravel and crazy paving.
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To clarify things, I am posting this diagram of my construction, thanks
http://img72.imageshack.us/img72/7358/neighbourstrenchpipevu4.jpg
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On Sun, 13 May 2007 03:43:08 -0700, peternoon wrote:

Yup! That's what I wanted to know. As I previously stated, if the trench was up to 300mm wide you could probably get away with finishing the job off.
As the trench is 500-550mm then I would advise you get some more advice. Maybe someone in this or another NG with engineering qualifications would be better suited to helping you.
You could finish the job off and it might be ok so long as the biggest car that'll ever drive over it is a Nissan Micra. I'd worry if you had an XJ6 or even worse a Rolls-Royce.
I hope you see my point. Replacing the top layers now might work, but then again it might not.
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Thanks for the reply, but what do you think might happen, that the concrete slabs could sink or something like this?

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On Sun, 13 May 2007 09:33:22 -0700, peternoon wrote:

Well if the trench is too wide and a large weight were to sit on the crazy paving over the line of flags there is the possibility that one or more of the flags could snap, and everything would collapse into the trench. Unless the flags are reinforced, which is doubtful.
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