Increased blast size with controlled vibration levels
Maliakhera Mines and Karunda Mines are surrounded by villages, which are at present, around 500 metres and above from the working benches. A new crusher has been set up to be fed from both the mines. With the new crusher coming in, the production rate would double up to 12000 tonnes per day from a single mine. Moreover, as the mines will expand in the future, the distance with the villages will be decreased, but it will be no less than 300 metres.
Following are the main problems mines management was facing in their operations:
• Small blasts due to higher vibration levels near the village
• Non-availability of established benchmark blast designs to carry out bigger blasts to meet the production demand of 12000 MT/ day
• Acceptable fragmentation with reduced vibration levels at POIs
At the outset, a meeting was held between Orica management and JK Cement works, Nimbahera management to discuss the issue and ascertain the problem with a sustainable solution.
After scoping the site and its expansion plans for criticality, Orica proposed Advanced Vibration Management (AVM) services to deal with the situation. The agreed key deliverables were:
• Keeping ground vibration levels below 2 mm/s at POIs at 95% confidence limit
• To increase the size of the blast in all areas and establish Drill & Blast designs
• Acceptable fragmentation levels to be fed to primary crusher
Orica used Unitronic™ Blasting System for site constants estimations and blast trials of suggested blast designs. After accurate data collection of vibration levels at different distances from the blast, and simulating blasts with Monte-Carlo Simulation Model, Orica planned to divide the mines into three zones based on criticality:
• Severe (less than 500 metres from the village)
• Critical (less than 600 metres from the village), and
• Safe (where village is more than 600 metres away).
A mutually agreed decision was made to go for deck charging in the severe zone of the mines, and suggested initiation pattern in the critical and the safe zone. Based on the predictions of Monte-Carlo Simulation Model and Firing Time Optimisation tool, Orica benchmarked Drill and Blast designs in the present working benches.
The following benefits were realised:
• Blast size in the severe zone of the mines was increased three-fold with Peak Particle Velocity (PPV) not exceeding 1.5 mm/s at POIs.
• The blast size in the critical zone was increased to 30 or more holes and 50 or more holes in the safe zone, which would generate at least 11000 tonnes and 16000 tonnes respectively, from a single blast.
• With deck blasting in the severe zone, the benchmark PPV of 1.5 mm/s was achieved at 300 metres with increased holes.
• Mine-wise Drill & Blast designs were established to be followed by the mines to continue achieving desired results.
To read the whole Case Study and the Testimonial from JK Cement Works, Nimbahera, please download it here>