Abstract: A series of undrained strain-controlled cyclic triaxial tests was conducted on saturated Nansha coral sand. The properties of initial maximum shear modulus, of coral sand and the degradation properties of the maximum shear modulus, of coral sand during the cyclic loading were analyzed. The of coral sand is greater than that of terrigenous sands. Compared with terrigenous sands, the effective confining pressure, has stronger influence on the of coral sand. The difference between the values of coral sand and terrigenous sands is due to the irregular shapes and the inner pore of the coral sand grains. The of coral sand is determined by the slopes of the hysteresis loop at the stress reversal points. The degradation of the maximum shear modulus during the cyclic loading is caused by the increasing excess pore pressure and the structure damage of coral sand. The of coral sand decreases faster than that of terrigenous sands with the increasing excess pore pressure ratio, . The existing models for the prediction of of terrigenous sand were established by the relationship between and , and it is not applicable to coral sand. Based on the elastic strain energy theory, a new damage parameter, is introduced to research the relationship between / and of coral sand. Finally, a new prediction model of coral sand was proposed.

Key words: coral sand, maximum shear modulus, damage state, elastic strain energy, cyclic triaxial test