In the article the results of tests of loams by static, dynamic and cyclic loads are given. Simple shift (cutting) is typical for soil deformation in natural conditions. At an increase of tangential stresses up to a limiting value the simple shift is completed by exhausting their strengths with break or without break of material uniformity. Shear strength is the basic strength parameter of soils in general and clay soils in particular. The estimation of shear strength of clay soils by tests in conditions of simple shift by static, dynamic and cyclic loads was considered. The diagrams of limiting state confirming the influence of lowfrequency vibration on strength characteristics of cohesive soils were obtained.