Phenomenology of control blasting in close proximity to densely populated communities-A case study of Mopan's area J open pit

Blasting is the process of fracturing material through the detonation of industrial explosives
placed into drilled holes suitably located to a free surface. Every blast hole containing a
calculated amount of explosive charge undergoes impulsive loading when detonated and
results in the dynamic transfer of a powerful shock wave to the surrounding rock. It is this
shock wave that brings about rock breakage when the tensile stress is produced after the
stress wave reflects on the free face or change in material density of rock material tensile
strength. However, this shock wave comes along with unwanted destructive consequences
such as ground vibration, noise and flyrock.
The consequences highlighted above are likely to affect the Wusakile Community in Kitwe
as Mopani Copper Mines (MCM) Plc. wishes to expand the pit towards the community that
lies within 150m from the pit rim. As part of the commitment given by MCM to the Zambia
Environmental Management Agency (ZEMA), all blasting operations close to a community
must maintain at least below the maximum vibration threshold of 10 mm/s with no flyrock.
Furthermore, all noise levels must be kept below the maximum threshold of 134dB in order
to reduce environmental concerns raised by the community. In order to meet the above
requirement, the phenomenology of rock breakage and other factors such as the maximum
projection distance, size of the fragment, shape of the fragment, angle of projection, the state
of confinement of an explosive charge, design faults, deviation in implementation and
unforeseen geological conditions were considered during the study.
Analysis of data showed that vibrations directed towards the community were kept below the
maximum acceptable limit of 10mm/s. Furthermore, all higher vibration readings recorded at
MCM Synclinorium offices were quickly dumped on the subsequent seismograph positions
located at Kalela Basic School thereby confirming its dumping effect. In addition, no flyrock
was observed to have gone beyond the safe blast limit of 100m and over 90% of crack
monitors on cracked houses revealed no expansion during the project life.
This dissertation therefore illustrates the possibility of conducting blasting operations close to
a community with improved fragmentation while mitigating all adverse effects to the
environment by use of controlled blasting techniques. It further suggests the possibility of
incorporating such blasting techniques and their threshold values onto the Zambian
Regulations.