EVALUATION OF BLASTABILITY CHARACTERISTICS OF SELECTED ROCKS USING ROCKMASS CLASSIFICATION FOR EXPLOSIVES SELECTION

Abstract

The research work evaluates the blastability characteristics of dolomitic marble in Glister Success Limited, Alaguntan, Oyo state and granodiorite in FCC Quarry, Akure, Ondo State, using rock mass classification for explosive selection. Rock samples were collected from these quarries and tested in laboratory for point load strength index using point load tester. Uniaxial compressive strength was estimated from the point load strength index result. The hardness test was carried out in- situ using schmidt hammer while the specific gravity was carried out in accordance with International Society of Rock Mechanic Commission (ISRM). Geological data, joint spacing, dip and dip direction were determined in the field using compass clinometer. The explosive was selected using the relationship between the mean fracture spacing and geomechanical properties. The petrographic analysis was also carried out on the samples to determine their mineralogy constituent. The results of the various analyses showed that the mean point load strength index value for dolomitic marble and granodiorite are 3.52 MPa and 4.37 MPa respectively, classified as high strength while the estimated mean uniaxial compressive strength value for dolomitic marble and granodiorite samples are 93.55 MPa and 111.05 MPa respectively classified as very high strength. The mean specific gravity value for dolomitic marble and granodiorite are 2.72 and 2.75 respectively. The mean results of Volumetric Joint Count, Rock Quality Designation (RQD), Rock Mass Rating (RMR) and Blastability Index (BI) for dolomitic marble are 2.55 m, 106.59, 82, and 55.5 respectively while the mean result of granodiorite are 2.16 m, 107.88, 79, and 57.88 respectively. The mean joint orientation value for dolomitic marble and granodiorite are 240 and 270 dip while dip direction was 1430 and 1170 respectively. The mean fracture spacing for dolomitic marble and granodiorite are 1.59 m and 1.90 m respectively. ANFO was selected for dolomitic marble while Slurry, Nitro-glycerine based explosive and ANFO were selected for the granodiorite. The results of the petrographic analysis showed that four minerals biotite (26.53%), plagioclase (20.41%), quartz (34.69%) and hornblende (6.12%) were present in the granodiorite while two minerals calcite (25%) and dolomite (62.5%) are present in dolomitic marble. Others are opaque. The blastability parameters were correlated with the Rock Quality Designation (RQD), Rock Mass Rating (RMR), and Blastability Index (BI) using SPSS for both dolomitic marble and granodiorite rock will assist in predicting the variables when data are supplied. The result revealed that strong relationship which is positive exists among the parameters correlated for both dolomitic marble and granodiorite. The result obtained will serve as a guide to mining engineers in selection of appropriate explosive for rock having similar characteristics