"No such thing as a small mistake"
A lot have people have probably seen the picture of two sides of a bridge not quite meeting in the middle with the caption "In civil engineering there's no such thing as a small mistake" which looks far too perfectly wrong to be real.

Things like this do happen on occasion though:
There was a story of a local engineer who set out the corners of some council houses that were all L shaped. Unfortunately he put one the wrong way around and nobody realised until after they started building it. Apparently the engineer walked to the beach, to the sea and just kept walking and was never seen again...

While I was at uni one of the engineers I knew from the company I was working for in the holidays had been banished out on site. Among other things he was responsible for setting out start/end points and levels for sewers. Not your normal household sewer but huge ones you could walk through which required big deep holes and lots and lots of stone bedding. To save time one company started at the top and the other at the bottom but when they got to the middle they were about 1m out (he'd forgotten to carry the 1 or something). In the end a couple of hundred metres of this very expensive pipe run had to be taken out and relaid, some of it had already been backfilled as well.

Apologies for size, but they were quite big mistakes.
( thistle, Thu 25 Oct 2007, 20:09, 2 replies)

In Syracuse NY in the 80s
a sudden sinkhole appeared in a couple of front yards.

It turned out that a brick storm sewer, about 12' wide and about as tall, was built about a hundred years before. At the time the surveyor in the tunnel blew an angle and they ended up a couple of hundred feet outside of the easement. So he did what any sane person who was working in a tunnel with men using picks and shovels to dig all day who would resent knowing that they had dug several hundred feet of tunnel in the wrong place would do- he made a couple of corrections and eventually got back to the easement, and carried that secret to his grave.

I think the state ended up just repairing the thing and settling with the property owners.
( The Resident Loon Not a demographic. Do not measure., Thu 25 Oct 2007, 23:10, closed)

Wrong map
A mate of mine had a temporary job in local government.

He was just there to do some basic computing work but, as is the way, ended up filling in for his way more experienced colleagues.

He was asked to print off a street plan of a certain location and to make sure he included all pipes/cables etc.

So he printed off the map, a bloke came round to collect it, and that was that as far as he was concerned.

Until, several days later when he was asked about the map printout. It seems he'd printed the wrong section of street. Instead of tearing up the surface and finding the relevant section of pipework, they found nothing.

Cue two days of umpteen specialist teams digging up most of the stretch of road in search of a missing pipeline. Of course, nobody questioned the veracity of the map as that would be just stupid wouldn't it?
(Fanta Menace Is tall enough to see over the fence, Fri 26 Oct 2007, 13:21, closed)