ABSTRACT
ABSTRACTIn room and pillar mining in jointed rock, bothroom and pillar dimensions are governed by the structuralcharacteristics of the rock mass. The techniquesof engineering geology in determining such dimensionsis reviewed and then applied for the case where theoverall plan dimensions of the stopes are restrictedand the pillars are slender. Techniques are examinedfor the collection of data on orientation, spacing,persistance and roughness. Methods are outlined fordetermining support of wedges in exposed pillar wallsand for the statistical treatment of pillar failure byjoint transection. Unstable roof blocks are determinedby the limiting horizontal stress across the roof ordensity of artificial support.The simple results of the application of engineeringgeology to room and pillar behaviour compared wellwith observations. Slender pillars had an effectivepost yield characteristic with a field loading similarto that calculated for simple joint transection. Mostmodels of pillar load and deformation rely too heavilyon intact rock parameters and appear irrelevant toactual performance of such pillars.INTRODUCTIONMost examinations of pillar design and performancein hard rock mining are based on studies of intact rockbehaviour. However for slender pillars the geologicaldiscontinuities are extremely important and the conventionalapproaches to hard rock pillar design becomeirrelevant. This paper examines the role of engineeringgeology in understanding the performance of pillarsand in dimensioning room and pillars in jointed rock.Data collection is illustrated with reference to theDolphin orebody of King Island Scheelite at King IslandAustralia. The performance of many slender pillars inthe orebody has been monitored over the past four yearsand the expected behaviour is compared with the observedfield response.The Dolphin orebody is a shallow-dipping wideorebody situated on the south-east shores of KingIsland. Mining commenced with a open pit operation,
