NEW METHOD TO OBTAIN OPTIMUM PRESPLITTING SPL ITTING DESIGN CRITERIA CONSIDERING CONSIDERING THE ROCK MASS PROPERTIES
1 Al varr o Gonzal ez, Car Alva Car lo s M uñ oz , Álvar Álvar o Andrades Sou outt h Regi Region on Techni Techni cal Ser Servi vices ces,, Ori Ori ca Min M inin ing g Ser Servi vices ces-LA -LAT TAM 1
[email protected]
As i ex 2012
Why Why Wall Contr Control? ol? Wall Control Control is directly related to: Sustainability Mining
Costs Mining plans and opportunity cost Productivity Mine profitability
Typical Wall Control values
>15 MUSD/Year
The influence of rock blasting in the slope stability Vibrations & resonance in the far fiel Pre-Split & Buffer rows
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The influence of rock blasting in the slope stability Typical blast damage over benches
The influence of rock blasting in the slope stability
The Pre-Splitting practice-An introduction • Is the most used technique in the named “controlled blasting”. • Basically it consist in to obtain a pre-split plane that permit to control the rock blasting damage. • To control and reduce seismic vibrations from the rock blasting. • To reduce back break and reopening of preexisting geological structures. • Safety of people and equipments working around benches. • Maintain integrity of benches, final highwalls and overall pit slope angle. • To reduce bench remediation costs.
The Pre-Splitting practices-An introduction •
Pre Split design is directly related to buffer row design
• Basically the pre-split practice consist of detonates two simultaneous de-coupled explosives charge spaced to a S distance
The detonation of the explosive charges produces a stress that it is transmitted to the rock massif in form of shock wave and gas pressure. The last one is considered as the responsible for the creation of the pre-split planes.
• The objectives is to obtain a pre-split plane that permit to reduce damage related to rock blasting
The Pre-Splitting practices-An introduction The most used formula for to obtain the S distance between two de-coupled charges at which the pre-split plane can be obtained is based on Sanden (1974)
Current methods consider only the static tensile strength and a constant decay of borehole pressure with the square of distance.
The Pre-Splitting practices-An introduction Current methods can not be scaled to rock massif
Dynamic method for pre-splitting design The dynamic method to pre-split design follows the work developed for Liu and Katsabanis (1993) and Onederra et al (2004) The pressure decay proposed by Liu and Katsabanis;
Ro
r
Relation between Vp and Pre-Split Spacing
Relation between RQD and Pre-Split Spacing Análisis para un macizo fracturado con Vp < 3,000 m/s, RQD<65% RCU:60 Mpa RQD:65% Disminu ción de RQD
RCU:60 Mpa RQD:60%
RCU:60 Mpa RQD:<50%
Relation between density and Pre-Split Spacing
2.3 ton/mt³ 2.6 ton/mt³ 2.8 ton/mt³
4.7 ton/mt³
Método canadiense
Application of dynamic method, case study n°1 Pre-split design in argilic andesites
Current pr e-split spacing = 2.2 m Dymani c met hod=1.8-1.9 m
Application of dynamic method, case study n°1 Case study area
BANCO 495
Filtro de precrote 65%
BANCO 480 Current pre-split design
BANCO 465
Application of dynamic method, case study n°2 Pre-split design in chlorite metandesites
Current pr e-split spacing = 1.8 m Dymani c met hod=1.2 m
Current pre-split design
Case study area
Application of dynamic method, case study n°3 Pre-split design in Qz-Sericite Granodiorite
Current pr e-split spacing = 0.9-0.7 m Dymanic met hod=1.3 m
Results with S=1.8 m Results with S=1.3 m (Dynamic method)
Design achieved with S=1.3 m
Conclusion
The new method proposed considers Vp and Ed as a relevant variables into the borehole pressure decay factor. Therefore geotechnical properties are contemplate.
Geotechnical properties of rock massif can be evaluated by cross hole techniques (Vp).
The spacing of pre-split holes can be obtained for different geotechnical domains follow the dynamic method.
Dynamic methods demonstrates Improvements in bench quality and bench design achieved.
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