They are incorporated with the soil classification systems, and in some cases they are related to the mechanical properties. It is the water content at 25 blows and can be determined by using Casagrande Cup.
Strength is considered to be the ability of a material to resist failure.
The behavior of a soil mass is controlled not only by the external total stress but also by the water and air pressures developed in the pores of the soil. In particular, that part of the total stress applied to a soil which is carried by the soil skeleton must be separated from the part carried by the water and air phases. Thus, all shear stresses applied to a soil must be carried by interpartile forces in soil skeleton, but in general only a proportion of the normal stresses will be carried by the soil skeleton. In the direct shear and the triaxial tests the three methods can be performed. In the unconfined compression test the first method is the only one that can be applied.