In clay science, the initial stage of consolidation compression of a clay, which is governed by the dissipation of excess pore water pressure (i.e., pore water pressure in excess of the hydrostatic water pressure). During this stage, the excess pore water pressure changes (usually approaching the hydrostatic water pressure), and the clay either produces pore water (in the case of positive excess water pressure) or adsorbs water into the pores (in the case of negative excess water pressure). During this stage, the effective stress changes, and the clay volume changes as well.
Cf., compression, secondary