Assessment of Excavation Method of Obajana and Ewekoro Limestone Deposits

Abstract

The research work assessed the optimum excavation method of limestone deposits at Obajana in Kogi State and Ewekoro in Ogun state. Geological mapping was carried out to measure the orientations of discontinuities. The orientation data obtained were plotted on stereonets to determine pole concentration and major joint sets using Dips 5.0 software from Rocscience. Two joint sets were identified in Obajana with orientations of 72 0 /089 0 and 88 0 /221 0 while three joint sets with orientations of 61 0 /048 0 , 16 0 /280 0 and 90 0 /140 0 were identified in Ewekoro quarry face. Schmidt hammer hardness and Unit weight tests were performed. The results obtained were used to evaluate the Uniaxial Compressive Strength (UCS) and consequently, the Point load index (I s) of the rock studied. The excavation method was assessed using Discontinuity Spacing Index (I f), the Point load index (I s) and the Geological Strength Index (GSI). The discontinuity spacing index was evaluated from the major joint sets identified and the determination of the volumetric joint count (J v).The geological strength index was estimated using an inbuilt chart of RocLab 1.0 from Rocscience. Excavation assessments revealed that "Very Hard Ripping" is a possible method of excavating Obajana and Ewekoro Type III deposits while the less dense Type I deposit of Ewekoro can be "Ripped". The only feasible excavation method for Ewekoro type II deposit is "Blasting".