mechanical analysis . Determination of the particle-size distribution of a soil, sediment, or rock by screening, sieving, or other means of mechanical separation; "the quantitative expression of the size-frequency distribution of particles in granular, fragmental, or powdered material" (Krumbein and Pettijohn, 1938, p.91). It is usually expressed in percentage by weight (and sometimes by number or count) of particles within specific size limits. See also: particle-size analysis.