Observations of ground collapse above shallow underground coal mine workings on the Stockton Plateau, New Zealand

This paper presents a number of examples of different ground collapse mechanisms observed above shallow abandoned underground coal mine workings on the Stockton Plateau, and attempts to elucidate some of the underlying strata failure mechanics. The worked coal seam is typically 5-10 metres thick and overlain by 20-40 metres of interbedded mudstones and often massive moderately strong sandstones. Historic plans date the majority of mining back to the early to early 1900¿s and indicate a variety of styles of underground mining, with significant areas that have apparently been heavily extracted by a combination of pillar splitting, pillar robbing, gallery development and hydro mining, and/or severely affected by underground coal fires.