Large-diameter(300 mm) cyclic triaxial tests were conducted on morainic, non-plastic soil taken from the core of the 117 m high Mattmark dam in Switzerland with the objective to provide an estimate of excess pore pressure development and the deformations under cyclic loading caused by the strongest possible earthquake in that region.Variables considered were anisotropic consolidation stresses, cyclic stress amplitude and number of cycles as derived from a dynamic response analysis of the dam. The results indicated that the build up of excess pore pressures remained small but the deformations produced by cyclic loading could be substantial, i.e.exceeding 5 %.Analysis of seismic settlement,however, showed that the safety of the dam is not compromised.