"charles" wrote in message
...
In article m,
dennis@home wrote:


"The Natural Philosopher" wrote in message
...

tunnelling by definition means that you are going deep enough to make
cut and cover impractical

So how deep is that? 20 feet? 50 feet?

Its very hard to cut and cover under main roads, railways, etc. so they
frequently put in a shallow tunnel.

There are plenty of situations on the M25 where existing roads and
railways
have been put onto bridges. This would work for railways, too.

Not quite a tunnel running underneath a main road to avoid going under the
buildings either side though.

Its relatively easy to dig a couple of big holes either side of a railway
and then build a bridge under it.