Currently, the charging procedure for sublevel caving mining is carried out with no prior information of the rock mass condition. Thus, engineers are blindsided to unexpected rock conditions and ill-prepared to address issues associated with collapsing boreholes. This results on charging problems and, as consequence, bad fragmentation of the rock after blasting which difficult ore loading and transportation as the gravity flow of the rock is reduced.

This paper builds up the work done by Ghosh et al. (IJRMMS, 2018), to classify the geotechnical rock condition into five classes (solid rock, fractured rock, cave-in, minor and major cavity). From it, two applications based on the Measure While Drilling (MWD) technique have been developed: one for geotechnical rock condition of orebodies and the other for predicting the risk of collapse in boreholes. The work of Ghosh et al. has been improved into a geotechnical rock condition block model to simplify the quantitative assessment and automatic recognition of rock trends. A thorough correction of the MWD parameters has been also applied to minimize external influences other than the rock mass. From it, the risk of borehole collapses model has been developed by comparing different combinations of the geotechnical rock condition block-model with the charging length of 102 production fan-holes. The assessment of the number of collapsed and non-collapsed blastholes and the charging length/blasthole length ratio has been used to assign high, medium or low risk of collapse to each combination. The results predict collapses in the first half of the fan-holes for the high risk, collapses in the second half of the fan-hole for the medium risk and no collapses along the hole for the non-risk holes. The two models have been applied in large scale for two orebodies in the Malmberget mine, Sweden, which comprises 20 drifts and 5060 fan shape long-holes.