Question $3$: Perimeter design $(40$ marks$)$

A platinum mine in the Limpopo Province is experiencing problems with the final pit wall in that several small, localized slope failures have occurred during the last few months. The Group Geotechnical Engineer $($GGE$)$ has been tasked to re$-$visit the drill and blast designs and asked for your assistance.

On visiting the mine, you obtain the following blast parameters:

Explosive Products:

$$ ANFO

$$ Emulsion $45$mm x $560$mm cartridges

$150$g boosters

$$ Shocktube $500$msec x $15$m

$$ Shocktube assemblies: $42$msec x $8$m & $100$msec x $8$m

Pre$-$split: $152$mm holes, $83-$degree inclination $12\mathrm{.}5$m vertical depth

Splitting factor: $0\mathrm{.}63$kg$/$m$2$

Hole spacing: $1\mathrm{.}4$m

Production Blast holes:

Hole diameter $168$mm; $12\mathrm{.}5$m hole length $($vertical$)$; stemming $4\mathrm{.}5$m; subdrill $2\mathrm{.}5$m

B x S: $4\mathrm{.}5$m x $5\mathrm{.}5$m$,$ stand$-$off to pre$-$split $2\mathrm{.}7$m; minimum of $8$ rows