Extensive experimental studies have been focused on the cyclic behavior of saturated sand under free-field level ground conditions when subjected to earthquake loading. In many practical applications involving earth dams, slopes and buildings, however, soil elements are always subjected to initial static driving shear stresses on the horizontal planes. The impact of initial shear stresses on cyclic behavior and strength of sand is not yet fully understood. The focus of the present study is placed on the initial shear impact on the failure mechanisms of saturated sand varying from loose to dense state. Three distinctly different cyclic failure patterns have been identified. The most critical one is characterized by sudden, run-away deformation without any precautionary signal. The second failure mode is well known as cyclic mobility in which deformation takes place in double amplitude. The third type is the plastic axial strain accumulation in a single direction. It is shown that which failure pattern prevails is complicated, depending on the initial state of sand and the degree of stress reversal
