Optimization of blast design to improve fragmentation of limestone at Dire-Dawa Quarry, Eastern Ethiopia

Abstract This study focuses on optimizing blast design parameters to improve limestone fragmentation at the Dire-Dawa Limestone Quarry in Eastern Ethiopia. Efficient fragmentation is essential for enhancing quarry productivity, reducing operational costs, and conserving energy. The primary objective is to determine the optimal blasting geometry to achieve better fragment size distribution in muck piles. A combination of field measurements and laboratory tests were employed to evaluate existing blasting practices. Key parameters recorded on-site included bench height, burden, spacing, rock hardness (measured with Schmidt hammer rebound values), joint orientation (using a Brunton compass), joint spacing, and aperture. Laboratory analyses involved density measurements and point load testing to estimate the uniaxial compressive strength (UCS) of the rocks. Geotechnical properties were further assessed using Rocscience software tools. Fragmentation outcomes were analyzed using the Kuz-Ram empirical model and WipFrag image analysis software. Additional models estimated loading times and energy consumption. Results indicated that current blasting practices produced approximately 15% of oversized boulders exceeding the crusher’s feed capacity (1050 mm) and 30.17% of the fragments under 100 mm. The mean fragment size was 30 cm, which could potentially be optimized to 24.48 cm. Furthermore, loading time could be reduced from 81 to 76 s, and energy consumption for blasting decreased from 0.50 to 0.41 kWh/ton. To prevent oversized boulders, reduce energy costs, and ensure consistent fragmentation across downstream operations, it is strongly recommended that the current blast design be optimized based on site-specific rock mass characteristics.