Because of complexity about property of unsaturated soil

getting correlative strength parameters needed high and extract equipment

the difficulty is big so that its application is limited. Based on an analysis of strength theory of unsaturated soil

CD test of clay about different combination of water content and dry density is carried out with normal three-axis test. According to the theory of effective strength of soil

the effective strength of clay about water content and dry density is discussed

thus functions of total strength indexes are established that the effect of water content(saturation) and dry density can be considered. Study shows that strength of clay has close connection with water content and dry density. Moreover

the relation between cohesion

internal friction angle and water content(saturation) is conic

the relation between cohesion and dry density is linear

and the mutual effect of the both can be expressed by multiplication. Our research can be used as a reference application of project.