Stopping a 40 tonne boulder

Rachel Young at Stuff reports:

A 40-tonne boulder has been turned into a political football after it smashed into an unoccupied house in Christchurch’s Port Hills.

Earthquake Minister Gerry Brownlee said the rockfall, which may have been caused by the recent dry weather, vindicated the Government’s decision to take no risks when it came to red-zoning some Port Hill properties.

But some residents forced out of their homes by the Government’s zoning decisions still believe rock protection work is possible.

I would have thought a 40 tonne rock would convince people that safety should be a real concern, but it seems not.

But Sumner resident Phil Elmey, who has vowed to fight the red-zoning of his land, said the house in Finnsarby Place was in a “bowling alley”. He said most of the red-stickered houses could be saved if money was spent on rock protection work.

“Even a rock that size could be stopped by the right protection . . . We think it’s disgraceful that it hasn’t happened.”

I am not an engineer, and I suspect neither is Mr Elmey. But if anyone out there is, maybe you can give us some idea of what sort of protection will stop a 40 tonne rock from ploughing through a house? And what if it was 100 tonnes?

UPDATE: Mr Elmey is an engineer, so I am happy for him to assess his own risk. So long as he is willing to pay for the rock protection himself, and also recuse himself from cover by ACC, health and welfare in case any rocks fall – then he should be free to stay in his house at his own risk.