We don't have synonyms for heapstead yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are hempstead, hampstead and halstead.
(n) :
(mining, historical) The elevated framework of wood or iron at bank, to the top of which the pit is continued above the surface, to provide the necessary height to pass the coals over the skreens into the wagons.
(n) :
(mining, historical) The elevated framework of wood or iron at bank, to the top of which the pit is continued above the surface, to provide the necessary height to pass the coals over the skreens into the wagons.