Evaluation of In Situ Modulus of Compacted Subgrades Using Portable Falling Weight Deflectometer and Plate-Bearing Load Test

In order to evaluate material characteristics (in situ modulus) of well-compacted subgrades, the portable falling weight deflectometer (PFWD) test, which simulates dynamic loads, was adopted. The falling energy was assumed as a dynamic load and a well-compacted subgrade was treated as an ideal elastic body. In addition, the static plate-bearing load test (PBLT) was used to evaluate the coefficient of subgrade reaction. The PFWD test and PBLT for a total of 22 testing points were carried out on well-compacted subgrades at two different highway construction sites (A and B). Three falling heights and weights were used to produce six different levels of dynamic loads. The test results show that there is a reasonable linear correlation between the dynamic deflection modulus and the coefficient of subgrade reaction of well-compacted subgrades. It was also found that the dynamic deflection modulus is not largely affected by variation of the falling energies. Application of the PFWD for compaction control and as an alternative method to the PBLT would lead to significant cost savings.