Usually requires D11,s in the middle of Sydney and many excavators with special equipment, allways fun jobs for the fitters. http://www.youtube.com/watch?v=7JCFfZmosUM
Drill and blast it! 1:3 angle, carefull blasting with redused Q and single whole ignition. Watching that D11 ++ all the exc struggling must make it cheaper to blast..
Im going to take a guess that the city does not allow explosives used.
Mee too... But big hammers and other heavy stuff make the same amount of vibration as carefull blasting. Easiest solution is to ban explosives, if you don't know how to set the limits. That sandstone could be well suited for blasting; soft compared to rock(low amount of explosives/volume) and vibration dampening so the vibration stops in a short distance. A firm here made a tunnel 20m/60feet under the streets with few notising what they where doing. Under buildings and all. Funny picture of the security guy in the street wearing tunnel equipment watching if any traffic light systems suffered when blasting right under.
Blasting is not allowed, some of these jobs have many rail, water and power tunnels within metres of them.Not to mention buildings usually right next door.