coefficient of active earth pressure
Technical term used in civil engineering and soil mechanics. Refers to the ratio of horizontal to vertical effective stress when a soil mass is allowed to yield sufficiently to mobilize its shear strength.
The coefficient of active earth pressure is an important parameter in retaining wall design.
Compound of 主働 (active, from 主 'main' and 働 'work') + 土圧 (earth pressure) + 係数 (coefficient). A direct translation of the English engineering term.