Short-delay blasting with single free surface: Results of experimental tests

Abstract Delay blasting with relatively long-delay intervals is widely used in mining engineering since the former detonated blast-holes can produce new free surfaces for the later detonated blast-holes. With the application of electronic detonators, which have a minimum delay and a delay accuracy of 1 ms, a new blasting pattern using short-delay intervals is proposed in the present study in order to improve rock breaking and control blast-induced vibrations in cutting blasting with single free surface in underground mines. Theoretical analyses are firstly conducted to investigate the mechanisms of blasting crater formation and vibration reduction of short-delay blasting. Then a series of blasting crater tests with different delay intervals are performed to compare the characteristics of blasting craters and blast-induced vibrations produced by short-delay and simultaneous blastings. The results of crater sizes show that it is possible to form a common blasting crater only when the delay intervals are shorter than the formation time of a new free surface. It is also found that the short-delay blasting can effectively reduce PPV compared with the simultaneous blasting, particularly in the near-field. Spectral analysis indicates that there is less energy in the low-frequency content in short-delay blasting than simultaneous blasting. The possibility and feasibility of reducing vibration via short-delay blasting in underground mines are also discussed in this study.

[1]  D. P. Blair,et al.  Non-linear superposition models of blast vibration , 2008 .

[2]  Xiuzhi Shi,et al.  Application of Hilbert-Huang transform based delay time identification in optimization of short millisecond blasting , 2016 .

[3]  Daniel Johansson,et al.  Stress Wave Interaction Between Two Adjacent Blast Holes , 2016, Rock Mechanics and Rock Engineering.

[4]  Zheming Zhu,et al.  Numerical prediction of crater blasting and bench blasting , 2009 .

[5]  C. Dowding.  Blast vibration monitoring and control , 2004 .

[6]  C S Wu,et al.  Blasting in twin tunnels with small spacing and its vibration control , 2004 .

[7]  G. Ghodrati Amiri,et al.  Comparison of Different Methods of Wavelet and Wavelet Packet Transform in Processing Ground Motion Records , 2009 .

[8]  M. Stagg.  Influence of blast delay time on rock fragmentation: One-tenth scale tests , 1987 .

[9]  Yi Luo,et al.  A study of smooth wall blasting fracture mechanisms using the Timing Sequence Control Method , 2017 .

[10]  Chen Shou-ru.  Explosive blasted per delay and burden effects on the time-frequency characteristic of vibration induced by blast , 2009 .

[11]  G. R. Abrahamson,et al.  The dynamics of explosion and its use , 1979 .

[12]  Per-Anders Persson,et al.  Rock Blasting and Explosives Engineering , 1993 .

[13]  R. D. Ambrosini,et al.  Size of craters produced by explosive charges on or above the ground surface , 2002 .

[14]  C. Kuzu,et al.  The importance of site-specific characters in prediction models for blast-induced ground vibrations , 2008 .

[15]  T. Singh,et al.  Evaluation of blast-induced ground vibration predictors , 2007 .

[16]  D. P. Blair.  Blast vibration control in the presence of delay scatter and random fluctuations between blastholes , 1993 .

[17]  R. Nateghi.  Evaluation of blast induced ground vibration for minimizing negative effects on surrounding structures , 2012 .

[18]  Xibing Li,et al.  Impact of blasting parameters on vibration signal spectrum: Determination and statistical evidence , 2015 .

[19]  Hong Hao,et al.  Characterisation of underground blast-induced ground motions from large-scale field tests , 2003 .

[20]  G. Valentine,et al.  Scaling multiblast craters: General approach and application to volcanic craters , 2015 .

[21]  Daniel Johansson,et al.  Numerical modelling for blast-induced fragmentation in sublevel caving mines , 2017 .

[22]  X. Z. Shi,et al.  Delay time optimization in blasting operations for mitigating the vibration-effects on final pit walls' stability , 2011 .

[23]  Chuangbing Zhou,et al.  Frequency comparison of blast-induced vibration per delay for the full-face millisecond delay blasting in underground opening excavation , 2016 .

[24]  Lin Tian,et al.  A Study on the Vibration Frequency of Blasting Excavation in Highly Stressed Rock Masses , 2016, Rock Mechanics and Rock Engineering.

[25]  Jian Zhou,et al.  A Comparative Study of Ground and Underground Vibrations Induced by Bench Blasting , 2016 .

[26]  G.G.U. Aldas,et al.  Waveform analysis in mitigation of blast-induced vibrations , 2008 .

[27]  P. D. Katsabanis,et al.  Timing effects on the fragmentation of small scale blocks of granodiorite , 2006 .

[28]  S. Mchugh.  Crack extension caused by internal gas pressure compared with extension caused by tensile stress , 1983 .

[29]  G. F. Kinney,et al.  Explosive Shocks in Air , 1985 .

[30]  Daniel Johansson,et al.  Shock Wave Interactions in Rock Blasting: the Use of Short Delays to Improve Fragmentation in Model-Scale , 2012, Rock Mechanics and Rock Engineering.

[31]  R. L. Parrish,et al.  Development of a predictive capability for oil shale rubblization: Result of recent cratering experiments , 1984 .

[32]  Gento Mogi,et al.  Optimum delay interval design in delay blasting , 2000 .

[33]  Daniel Johansson,et al.  Numerical simulation for the influence of delay time on the rock fragmentation , 2013 .

[34]  Jessie L. Bonner,et al.  Quantification of ground vibration differences from well-confined single-hole explosions with variable velocity of detonation , 2010 .