Abstract: The problem of strength, liquefaction and failure of saturated sands has always been greatly concerned in dealing with the safety of foundations of hydraulic structures and earth or earth-rock dams against earthquake action. The theory of limit equilibrium is adopted as a criterion in evaluation of the incipient failure state of saturated sands under cyclic loading, and the corresponding laboratory tests and analytical methods are suggested. The difference between liquefaction and incipient failure is clarified. Two types of approach are proposed for evaluation of pore water pressure changes induced by cyclic loading, in one of which their dispersion and dissipation behaviour is taken into account.