Rocking it

Re: MLA wants B.C. to carve a Canadian Mount Rushmore, Sept. 8

The proposal by ChilliwackHope MLA Laurie Throness to transform a mountain into a monumental sculpture is an interesting proposition. I teach and research rock mechanics design at the University of British Columbia, and I helped develop the three-dimensional fracture network model for the ongoing carving of the Crazy Horse Memorial in South Dakota in my previous career as a rock mechanics consultant.

The inherent challenge of a project like the MLA’s proposal or the Crazy Horse Memorial is the nature of the material. We may think of rock as something inherently strong, but while that may be true for a 10- centimetre rock sample, a monument of the scale proposed by Throness would involve rock mass, which includes intact rock material and fractures ( some of which may be tens of metres long, or even longer). The mechanical properties of those fractures would significantly impact the strength and deformability of the rock mass. Intersecting fractures would likely contribute to the formation of rock wedges that separate the rock mass into discrete pieces. The key challenge then is managing the instability of the rock mass.

The article mentioned using the stones removed from the mountain to pay for the project. In reality it’s far more likely that most of the byproduct of excavation would be of low economic value. And it’s important to remember that the costs of maintaining the monument — checking the stability of the rock mass, replacing the supports to keep pieces of rock from falling off — would be borne by future generations. Davide Elmo, Associate Professor, Rock Mechanics, University of British Columbia, Vancouver