done that, worked a treatWe dug a trench in our field next to the road nice and deep with a 16ton digger, dropped a fairly thick walled 2 inch pipe with a cap welded on the end in the trench and the digger pushed the pipe under the road.
Obviously this isn’t legal but no one ever knew any different and it did no damage to the road, the man driving the digger had done it many times, he just got one of us to watch the tarmac in case there was movement.
From memory he had dug a fairly large hole on the opposite side so we knew when to stop