PERMFILE116578

• Permit No: M1988112
• IBM Index Class Name: Permit File
• Doc Date: 3/2/1989
• Section_Exhibit Name: APPENDIX III PIT DESIGN BLAST CONTROL MONITORING
• Media Type: D
• Archive: No

1
Blazt Control
' 1 It is mdctl that cautious blazing be practiced iII the victairy of the ultimate wall 'T'his is required in
O[dCr CO maintain Clio s[rCIIg[h CharaCCerlSti6 Cha[ are 3IIhereIIC [O the maCCIiai
' Ashby (1982) has fisted the following factors that should be considered when blasting and ezcavatioa
near the final pit walls.
' o Careful shovel deaaiag of pit walls u usually justified, esnecally when developing steep slopes
or multiple benches.
o Considerable success has been reported from Bougainville Capper Miae where excavation or
' trimming [o slope limits has been achieved by means of bulldozers working towards the
shovels.
' o Backbreak or overbreak beyond the final wall limit is one of the major causes of wall dama¢e
and is obviously a waz[eful activity. Oae of the simplut modif~ca[ioas, that cw Lead [o
improvement in wall conditions, it that involving adequate allowaacL for batkbrnak behind the
' fmal wall blasu. The backbreak durance behind a blast u a function of the blast and the roclt
mass conditions Once as appropriate level of blazting control has been achieved, variation of
backbreak will be a function of rout type and structure. Diggable backbreak should be
reserved for each sat of geological conditions. Diable baclcbreak dis[ance can fie used az a
' design parameter in determining the du[aace tha[ the back of the blaz[hole pattern should be
offset from the fiIIai wall )a vices of the importance of "back rout' desi¢a adjacent to[ ea pi[
walls, dcsigII of the blazthole pattern from [he back [o the front of the rho[ may be justified,
t provided [haz front rOw COa[r01 G!II bC main~ained-
o la most production blazting and particttlariy when blastiry adjacent to pit walls, ntultipie-row
blasts should be avoided. iVfultipie-row or deep shots tend to 'choke", fire irregularly and
' cause overbrealc Approximately [hrr rows are optimum and the author feels that more than
five rows should be avoided Fgure L illustrates how, subject to operating widths constraints a
' pit expansion ctII be mined-out is a series of relatively small steps involving dri]Iimg, blasting,
and ucava[ioa back to ultimate pit ]imi[s. The sequence dou require slightly mart shove!
mobiluatioa than is necessary for "simie' pass m~ but the results generally justify use of
the method.
' ,.,i~i~i~~d
o S
d
ill
h
ld b
b
d i
l
l
li
b
i
d
h
d
lli
u
r
ou
-
s
e
an
II many razes mII
e comp
ete
y e
w
m
nate
en
rt
ng
holes adjacLIIt to pit walls. When loading holes adjacent to pit walls, main[enana of optimum
eapfosive rise and proper hole dcptlss is at leazt as important az loading normal productioII
' patterns. To maintain adequate charge dumbudoa and powder factor control, use of low-
streagth, low-density explosives is favoured, Figure 2
' o Good Marge distnbution is also achieved by using smaller-diameter buffer charges than for
the main productioII pattern. To mart='~ charge disruption and blasthole utilization,
smaller-diameter holes arc drilled oa a closer spaang. At many operatioIIS, the drilling of one
or more rows of buffer holes placed betwern the back of the main production pattern and the
' wall provides a significant improvemem is wall coadidoas Buffer charges are fired is delayed
sequenm with the main production pattern and have the major advantage over tratifitional
perimeter wall control because the rock is actually blasted rather than trimmed or split.
o Slope failure is a time-depeadrn[ pheaomeaoII and is frequeady predpi[a[ed by removal of
benches at the toe of a aitical slope. Slope monitoring by survey and visual means will usually
' provide warning of impending failure, provided that the raze of failure is fairly gradual
1
1