An Experimental Study to Assess the Shear Modulus Degradation by Fatigue of Mexico City Clay

In this research, the degradation by fatigue of Mexico City clay is studied using a triaxial equipment where the cyclic stress amplitude was maintained constant during the experiment. The variables considered in the study were the following: state of the soil, effective mean confining stress, magnitude of cyclic stress and number of loading cycles. Undisturbed samples, anisotropically and isotropically consolidated, were subjected to cyclic loading for this purpose. When analyzing the cyclic stress-strain response with the number of cycles a threshold of permanent deformation in function of the cyclic deviator stress and axial strain was found. When the cyclic strain exceeds this distinctive value the rate of permanent (plastic) deformations accumulate faster. For practical applications of computing permanent deformations in Mexico City a simplified method is proposed. This method considers the above threshold and a hyperbolic model to represent the cyclic response in Mexico City clays