No passenger trains today

At Harrogate station, the usual passenger trains have temporarily been replaced by wagons of ballast and various other types of heavy track maintenance machinery.
This army of rail workers were busy installing some new points and a line cross-over. Behind them two large and very noisy machines were slowly advancing along the tracks towards them. They appeared to be bedding down the ballast (see first extra), as there were big piston-like jacks at each side thumping the ground. (Any railway experts amongst you may be able to explain exactly what they were doing.) 
Exciting stuff for a Sunday afternoon!