For the aseismic design of a pier foundation constructed on a lightly cemented dense gravel deposit of a 3,910m-long suspension bridge, cyclic and monotonic undrained triaxial tests were performed on undisturbed specimens with a diameter of 30cm taken from the deposit under a sea depth of about 55m. Using the results of the cyclic undrained triaxial tests together with irregular cyclic stresses evaluated for the design earthquake motion by a dynamic FEM analysis, maximum strains in the gravel deposit were obtained by the cumulative damage concept. The strain values thus estimated indicated a sufficiently high degree of seismic stability of the foundation. Further, for the same initial mean Principal stress, the strength for monotonic undrained triaxial compression of isotropically consolidated specimens was found not greater than the strength against irregular cyclic undrained loading of the specimens anisotropically consolidated as in the field. This means that the former strength can be used as an approximated value of the latter
