Foundations and Abutments—Bennet and Mica Dams

Two large earthfill dams, one founded on rock, and the other on rock and overburden, illustrate foundation treatment for high earthfill dams in Western Canada in recent years. Strong glacial or fluvial materials were available for the embankments. Foundation rock was competent, although modest blanket and curtain grouting ensured reduction in permeability of foundation rock. In the core contact areas, rock surfaces were sculpted to remove sudden changes in profile, and treated with pneumatically applied mortar or dental concrete to ensure a satisfactory rock to fill bond. At the Bennett Dam, steep canyon walls were cut back to eliminate a corner at the top of the wall and thus reduce differential settlement. Near the top of the Mica abutment, rock was excavated to ensure that longitudinal compression was maintained in the core and downstream shell as the dam deflected under load. Observations to date indicate Bennett Dam is performing satisfactorily. Mica Dam is being extensively instrumented but assessment of its performance must await its completion in 1973.