Cambridgeshire County Council have done lots of this round here.
One particular bridleway used to be just a nice grassy lane, with a muddy section at the lowest point.
They had some money to improve countryside access for the new town of Northstowe. So they ripped it up, dumped a mixture of rubble, bits of plastic and general crud on it, covered it in gravelly crud and earth and then waited for Winter.
Winter duly came and it's now a churned up mess. I used to be able to cycle along without putting a foot down (it's only a bridleway next to a field) but that's impossible now. The middle section after some rain is just glooptastic mudfest madness.
This is a photo of an earlier section where it's actually passable. It's just ugly.
I've come to suspect that the people who work in Cambridgeshire County Council actively dislike the countryside.
EDIT: they cause way more damage than MXers ever could.