Potential Issues on MSE external stability design in light of the recent Canadian and AASHTO Bridge Design Codes

ABSTRACT: The paper examines differences between the Canadian and the American designs with respect to the external stability (bearing-sliding-eccentricity) of the MSE walls. It is noted that in general, the Canadian design is more conservative. A particular wall example founded on seismic Site Class C soils in an area in British Columbia at the border with USA is examined to provide a quantitative assessment of the conservatism in the Canadian design. The differences between the design results originate from some differences in the prescribed load factors, resistance factors, but more so from some major differences in the methods of evaluation of the seismic hazard and wall inertia forces. Both codes are ambiguous with respect to the effects of the load inclination on the foundation bearing resistances. In case of strong earthquakes, the load inclination factors may completely break down.