Jointing mains water pipe underground

Hi,
Another plumbing one...
At some point, I want to move where my water pipe enters the house (it goes up the outside wall right now and is susceptible to freezing). I'd like to bring it up through the wall/concrete floor (45 degree core drilling job) further along and put the main stop cock inside.
The supply pipe I have is blue plastic covered 15mm malleable copper (comes on a roll type of stuff) and was put in by the water company about 10 years back.
At the same time, I want to run as much as possible of the new section in 25mm MDPE, ready to upgrade the last leg back to the road when I have a reason to lift the drive.
Q1) Is it acceptable to have joints under the ground or will I need to make a little pit around it?
Q2) Whats the recognised way to joint plastic covered copper to MDPE? and later can I have an MDPE-MDPE joint underground?
Q3) Presumably, if I do bury it, I need to protect the exposed copper? Would I just over sleeve it with a bit of plastic waste pipe; or wrap with denso tape, or self-amalgamting tape?
Many thanks in advance :)
Cheers
Tim
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Why don't you box the supply pipe in, and fill the box with insulation? There seem to be all sorts of copper/plastic joints available so I'm sure you will find what you need. I have seen plenty of supply pipe joints go underground, so it must be OK. If you do replace a section of pipe, put it in some blue conduit (which I believe you are supposed to do anyway), so that when you come to replace the rest of the pipe, it'll be easy to replace the entire length.
T
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snipped-for-privacy@gmail.com coughed up some electrons that declared:

It's also partly that it's coming up in a less than ideal place - 2 birds, one stone sort of thing.
<snip>

That's a good idea.
Cheers
Tim
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You can get copper to MDPE compression joints in any plumbers merchants ... and fully acceptable to have them buried ... just cover with pea gravel wrap any exposed copper in Denso.
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Rick Hughes coughed up some electrons that declared:

Brilliant - thanks.

Excellent. I might combine this with Tom's ducting suggestion. The bit I'm extending is only about 4m long. There's another probably 12m to the road (takes the long route round a bend to avoid the trees). Re-threading the lot with a single length of pipe when doing the 12m bit wouldn't be a bad idea (One less joint near the foundations).
Thanks for that.
Cheers
Tim
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