5. Modulus of Subgrade

Objective - The modulus of subgrade reaction (k) is used for evaluation of strength of subgrade for roads, runway pavements and raft foundations. The k-value can be determined by field tests or by correlation with other tests. Ratio of load per unit area (applied through a centrally loaded rigid body) of horizontal surface of a mass of soil to corresponding settlement of the surface. It is determined as the slope of the secant drawn between the point corresponding to zero settlement and the point of 1.25 mm settlement of a load-settlement curve obtained from a plate load test on a soil using a 75 cm diameter or smaller loading plate with corrections for size of plate used.