Blasting Geometry Evaluation In Order To Produce Desired Fragmentation On Andesite Rock Blasting Activities At PT Mandiri Sejahtera Sentra, Purwakarta, West Java Province

Abstract

PT Mandiri Sejahtera Sentra is located in Kampung Pamoyanan, Sukamulya
Village, District Tegalwaru, Purwakarta, West Java. The company produces products such
as split andesite and graystone, with a 41.2 hectares concession area.
Breaking of andesite from the bedrock is conducted by blasting activities using
ANFO explosives and triggered by power gel. Staggered and rectangular blasting pattern is
used along parallel series of non-electric detonator.
Blasting activities carried out as many as 44 times In June, with a target of blasting
production in the month is 68.962 BCM. Production target per detonation is 1,567
BCM/Blasting.
The actual blasting geometry is as follow : burden ; 3 m, spacing ; 4 m, stemming ;
2 m and subdrilling; 0,5 m. It produces 24 % boulder (≥ 80 cm diameter). The company
expects that the study are able to reduce the amount of boulder.
Geometrical improvement has been done to solve those problems, not only by
comparing the actual detonation geometry design with the equation R. L. Ash and C. J.
Konya, but also considering the economical factors.
Based on the field observations, blasting activities obtained 24 % of boulder, instead
of 39,02 % (based on Kuz-Ram’s distribution fragmentation calculation theory). That being
said, there is a difference of as much as 15.02 %. Hence, geometrical improvement is
needed in order to get good fragmentation with boulder amount equal to 0 %.
The improvement produces blasting geometry (based on C.J. Konya’s theory) as
follow : burden ; 2,6 m, spacing ; 3,6 m, stemming ; 2,6 m and subdrilling ; 0,5 m. It will
produce 14,45 % boulder (size of ≥ 80 cm) with the use of Powder Factor 0,44 Kg/BCM.
C. J. Konya is chosen since it gives best result of the three existing blasting
geometry. It needs at least 14 blast holes to achieve 1.567 BCM’s production target.