With the aim of using granulated coal ash mixed with natural sand as geo-material, laboratory experiments were performed on the composite material to understand its cyclic shear characteristics. A series of undrained cyclic shear tests was performed on loose samples of the composite material to assess the effect of the mixed proportion on the cyclic shear characteristics. The tests revealed that (1) the composite material in which the proportion of granulated coal ash mixed was about 50% or more has cyclic shear strength almost equal to that of pure granulated coal ash, irrespective of the type of natural sand used ; (2) The cyclic shear strength of the composite material increased when the particle strength of the natural sand was low ; (3) When the composite material consisted of about 30% natural sand, the initial shear modulus G0 of the mixture was almost equal to that of granulated coal ash. Based on these test results, it was shown that when the mixed proportion of granulated coal ash was about 50%, the cyclic shear characteristics and dynamic deformation characteristics of the composite material were almost similar to those of pure granulated coal ash.
