Development of the Original Method for Highway Design

During 1928 and 1929, the California Division of Highways made an intensive investigation of pavement failures throughout the state. Areas that had failed were investigated to determine the local drainage conditions and other factors affecting the stability of the pavement. Holes were drilled through pavements and undisturbed samples were obtained which would furnish information as to density and moisture content of the materials underlying the pavement surface. These investigations pointed to three principal types of pavement failure: (1) By lateral displacement of the subgrade material as the result of the pavement having absorbed water and softened after construction; (2) by differential settlement of materials underlying the pavement; and (3) by excessive deflection of the materials underlying the pavement, resulting from repetitions of load.