In this paper, the effects of narrow and sloping canyons on the longitudinal dynamic response of earth dams is investigated by a simplified method for 3-D dynamic analysis. Analytical results for earth dams with several width to height ratios are compared with the results of plane strain solutions for comparable sections. For an embankment in a triangular valley with a width to height ratio of 1~2 and subjected to earthquake motions, the computed max. accelerations at the midsection were about 30 to 50% higher in a simplified 3-D response analysis than in a plane strain analysis. On the other hand the computed max. displacements, max. velocity, and max. shear stresses for the same section in 3-D analysis were generally about one half the values to 2/3 the values computed from plane strain analysis. It is concluded that the longitudinal dynamic response of an embankment is significantly affected by the width to height ratio of canyon in which it is constructed
