Determination of Resilient Modulus of Subgrade Using Cyclic Plate Loading Tests

Resilient modulus of subgrade is often necessary for pavement design and determined by cyclic triaxial tests or correlation with other laboratory or insitu test results (such as CBR and DCP data). Cyclic plate loading tests were conducted in this study to determine the resilient modulus of a weak subgrade. The weak subgrade was made of 75% Kansas River sand and 25% kaolin and compacted at wet of optimum in a large geotechnical testing box (2m x 2.2m x 2m). This subgrade was first evaluated by DCP tests and then tested under a 30-cm diameter rigid plate at four different magnitudes of cyclic loading. During the tests, the deformations of the plate and the subgrade surface were monitored. The test results showed that the plate deformation increased with the number of cycles. An elastic solution was used based on the rebound deformation of the plate to calculate the resilient modulus of the subgrade. The calculated resilient modulus of the subgrade decreased and approached a stable value with the number of cycles under different magnitudes of cyclic loading. The calculated resilient modulus from the cyclic plate loading tests was compared with that determined based on the correlation with the CBR value of the subgrade.