Rock­ing it

National Post (Latest Edition) - - LETTERS -

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

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