Abstract: Small scale production of coal in Indonesia began in 1849, increasing up until the Second World War. Indonesian coal was subsequently eclipsed by oil, until the oil crisis in the 1970s when production was assessed anew. During the 1980s and 1990s output has expanded massively, with much of the investment coming from abroad. The current coal industry including opencast coal mines, coal terminals, and coal types is reviewed. Indonesia is becoming an important exporter of low-sulphur, low-nitrogen coal. For the present Indonesian mines use small scale equipment, partly encouraged by some aspects of Indonesian mining law. As the industry becomes better established larger equipment may be used. 7 figs., 3 tabs.

Abstract: This paper presents the results of a recent study on the development of an in situ testing method for determining coal strength in mine pillars. The strength testing is performed in the horizontal holes drilled into the coal rib using a penetrometer, which is an hydraulically powered device that uses an indenter to press on the surface of the borehole until the load reaches the failure point of the coal. The pressure and the penetration of the loading pin are recorded by a data-acquisition unit. The results collected from several coal mines indicate that this testing method is ideally suited for the realistic coal strength measurements. The new testing system not only improves the accuracy of the pillar-strength determination, but it is more cost efficient than the conventional method. 8 refs., 4 figs., 3 tabs.