The modulus of subgrade reaction (k) is used as a primary input for?rigid pavement?design.? It estimates the support of the layers below a rigid pavement?surface course?(the?PCC?slab).? The k-value can be determined by field tests or by correlation with other tests. There is no direct laboratory procedure for determining k-value.
The value of k is in terms of MPa/m (pounds per square inch per inch of deflection, or pounds per cubic inch pci) and ranges from about 13.5 MPa/m (50 pci) for weak support, to over 270 MPa/m (1000 pci) for strong support.? Typically, the modulus of subgrade reaction is estimated from other strength/stiffness tests, however, in situ values can be measured using the plate bearing test.