Correspondence between John Nye and William [Bill] Ward concerning problems with backfilling abandoned mines Discussing issues around filling old mines to prevent subsidance. Ward was discussing the mechanics of the process with Nye. Includes theoretical calculations by Nye, illustrating how a pile of material being pumped into a mineshaft would behave, and letters from Ward discussing progress and issues with equipment. Includes reprints of two reports into the mine filling project. 1983-1985