In classical soil mechanics, many of theories are based on non-cohesive soils and normally consolidated saturated cohesive soils. Constitutive relations at present are actually developed on remolded or non-cohesive soils. In fact, soils in geotechnical engineering are often structural undisturbed and unsaturated. These soils have nothing in common with normally consolidated saturated soils, but none of theories is mature for them. Subgrade of existing railway is hard to be reinstated in a short time if its structural strength sustains losses. Thus it is necessary to study on mechanical behaviors and to protect structural strength and to develop test and appraise procedure for these soils. With equivalent suction including all factors which can increase the resistance against sliding between soils particles, the generalized effective stress(G.E.S.), a equivalent effective stress, comes out, and all kinds of soils are united in the G.E.S. theory [1,2] .In this paper for mentioned problems, the following items are researched with G.E.S.. 1 Study on Generalized Effective Stress and Mechanical Behaviors of Expansive Soils For the purpose of research the laws of influence on strength and soils shear wave velocity from water content or saturation degree, the paper takes expansive soils as subjects, then experimental phenomena are emphasized, and experimental factors are controlled easily. Based on the test and existing achievements [3,4] , the article suggests following results: ① Compression curves of expansive soils with different water content can be normalized by G.E.S.. ② For unsaturated soils swelling pressure reflects change of generalized suction. In this paper, it is verified once again that third strength theory [3,4] (τ s=p s tg φ,τ s=mp s tg φ) is effective , and believed that the modified coefficient m in the equation relates to the definition and measure method of swelling pressure. The reason for requirement of m is that the soil is still under O.C. state at the end of swelling pressure cons
