Red clay is of swelling properties in a similar way to expansive soils. Compared with common clayey soils

the strength behavior of red clay and expansive soils are more complicated. Strength of red clay and expansive soils

as the standard of shear resistance

is an important parameter used in evaluating stability of embankment slopes such canal

roadbed and earth dam. Many failure records of earth constructions due to red clay and expansive soil slopes and foundations require a definite understanding of strength of red clay and expansive soils. The strength characteristics of unsaturated red clay and expansive soils have been studied experimentally. The main features and influencing factors of strength behavior of red clay and expansive soils which are different from those of common clayey soils are discussed. The interrelationships between the shear strength parameters and water content of red clay and expansive soils are established on the basis of experimental data.