... his own consultancy and I still work with him when they have jobs including monitoring active railway arches. Active is the right term as well as I have seen videos of movement across a crack in an arch and a skewback of a viaduct moving backwards and forwards as trains passed over. During my study period the Transport and Road Research Laboratory had a program of eight tests to destruction on redundant arches and one brand new one that was built on the test floor in our laboratory at Dundee where my contracting experience proved very useful. 3137_290125_120000000.jpg 3137_290125_120000001.jpg The shiny discs were home designed pressure cells to measure the contact pressure between the fill and the arch ring. I also watched the demolition of an arch at Cargill on the old Caly main line from Perth to Aberdeen that was just up the road from where we lived at the time. A lot of time and money was wasted installing explosives into the arch when all that's needed is to simply lift the crown. Anyway the photo below shows the digger sitting on the solid masonry backing above and behind the abutment. ...