In (C) under bar onstruction (C) under bar ycle three (CC3) (L) under bar ow-strength (F) under bar lexible pavements with (C) under bar onventional aggregate base (LFC1, LFC2, LFC3, and LFC4) at National Airport Pavement Test Facility (NAPTF), a significant amount of rutting was observed in the subbase and in the subgrade. Profile measurements show that the rutting in the subgrade was accompanied by shear flow of the subgrade material. It is believed that the rutting in the subbase layer was caused mainly by consolidation. In-situ density measurements, using a 152-mm (6 in) diameter sand cone apparatus, were made at different depths in the subbase layer to study the rutting in the P-154 subbase layer. A theoretical equation was also derived to compute the change in layer thickness due to consolidation. The results show that a significant portion of the rutting in the subbase layer in LFC-2 was due to consolidation (or change in density) and not shear failure in the material. This compaction of the subbase layer also resulted in higher CBRs inside the wheel tracks. In LFC3 and LFC4, no significant changes in subbase densities were observed even though these two test items were considerably thicker than LFC-2 and were subjected to considerably more load applications.
