Abstract
Blasting is a major method of excavation in mining, civil construction and infrastructure projects. The integrity of the rockmass of the final wall after excavation is important for the stability and economics of the operation. Perimeter blasting achieves a planned surface of the rockmass. The pre-split is one such technique, deployed when there is no free face and, thus, involving several interactions of rockmass properties, including strength, joint spacing and joint orientation, with respect to blastholes, blast design, explosive configuration, blasthole deviations and other variables. The mechanism and models of the pre-split are perfunctory, particularly in defining interactions of pre-splitting variables. The basis of pre-splitting vis-à-vis dominant variables affecting performance is, accordingly, discussed here. Since the half cast factor, generally used for damage assessment, has its limitations, the index of blast damage has been compared while modelling performance. Models using response surface analysis for pre-splitting, for both blast damage index and half cast factor, were developed using historical data. The angle of the blasthole with respect to the major joint orientation, spacing of the joints, blasthole spacing, drill deviation, linear charge concentration and compressive strength has been used to compare the above-mentioned damage criteria. Blast damage index has been found to be a better predictor for determining rockmass damage due to blasting. The desirability of the variables deployed has been determined using optimization procedures. A fresh impetus to pre-split studies is expected to provide a ground for future research, particularly studies using advanced computational and numerical algorithms.
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Abbreviations
- S j/S b :
-
Ratio of joint spacing to pre-split hole spacing
- f(S j/S b):
-
Resolved values of Sj/Sb
- q lc :
-
Linear charge concentration (kg/m)
- θ :
-
Angle of inclination of blasthole between blasthole and major joint orientation in radians
- δ dd :
-
Drill deviation
- σ c :
-
Unconfined uniaxial compressive strength (weighted average) also referred to as UCS or uniaxial compressive strength of the rock
- σ t :
-
Tensile strength of intact rock
- σ td :
-
Dynamic tensile strength estimated from compressive strength
- d h :
-
Blasthole diameter
- p b :
-
Estimated blasthole pressure
- p n :
-
Normal component of blasthole pressure
- p t :
-
Tangential component of blasthole pressure
- v max :
-
Peak particle velocity
- ρ r :
-
Density of rock
- v p :
-
p-Wave velocity of rock
- k :
-
Rock constant
- I BD @1m:
-
Blast damage index calculated at 1 m from blasthole and HCF% is half cast factor percentage
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Acknowledgements
The author is thankful to the Director CSIR-Central Institute of Mining and Fuel Research, India, for his permission to publish the paper. The sponsorship of APGENCO is gratefully acknowledged. Thanks to all my colleagues for their help and cooperation during data generation. My profound thanks to Sri Ramesh for his critical views all along the study. Thanks to Suraj for help with references and Geeta and KP Madhu for critically examining the text for errors. Thanks to anonymous reviewers whose initial criticism has helped in improving the paper significantly.
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Raina, A.K. Influence of Joint Conditions and Blast Design on Pre-split Blasting Using Response Surface Analysis. Rock Mech Rock Eng 52, 4057–4070 (2019). https://doi.org/10.1007/s00603-019-01822-8
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DOI: https://doi.org/10.1007/s00603-019-01822-8