Civil and Building Engineering.

The shear strength of soil or rocks is the most important soil and rock property used by the foundation designer. The foundation designer will often base the selection of the foundation type on the shear strength and use the values for shear strength in computations of axial and lateral capacity of the foundation.

The manner in which shear strength of soil or rock is measured and characterized often depends on the type of soil or rock. Typically, the shear strength of cohesive and cohesionless soils is expressed using the Mohr-
Coulomb shearing parameters. Advanced constitutive models that are extensions and modification of the basic Mohr-Coulomb parameters are also used in major projects where additional soil investigations and laboratory tests are made.

Any implementation of the Mohr-Coulomb shearing parameters or any of the advanced models for shearing parameters will utilize the value of effective stress. Thus, the position of the water table must be known for their application.

The density, or unit weight, of the soil or rock is a soil property that is necessary for the computation of stresses due to gravity. The density of soil is computed using the weights of the solids in the soil and the weight of water in the soil. Any changes in soil density and volume that might arise from changes in the amount of water in the soil are computed if necessary.