Evaluation of constructing increased single-lift thicknesses of unbound aggregate bases: Case study in Georgia

J. L. Bueno, K. H. Stokoe, J. J. Allen, M. E. Kalinski

Research output: Contribution to journalArticlepeer-review

1 Scopus citations


A study was conducted to evaluate the feasibility of compacting unbound aggregate base courses in lifts thicker than those permitted by state departments of transportation (DOTs). At present, the majority of the state DOTs allow a maximum lift thickness of 20.3 cm (8 in.) or less. Work conducted in conjunction with the widening of a state road in Georgia is described. Three test pads of the same base material were constructed and evaluated: one Target Strip and two Test Sections. The Target Strip was placed in two lifts: a 17.8-cm (7-in.) lift followed by a 15.2-cm (6-in.) lift. Each test section was constructed in a single, 33-cm (13-in.) lift. Compaction of the unbound aggregate base courses was evaluated by conventional nuclear density gauge (NDG) testing. Additionally, nondestructive seismic testing was used to evaluate stiffness profiles within the base and supporting subgrade. Spectral-analysis-of-surface-waves (SASW) tests were used for this purpose. Both the NDG and the SASW test results show that a 33-cm (13-in.)-thick layer of unbound aggregate base can be compacted as dense and as stiff as a 15-cm (6-in.)-thick layer. The seismic results also show that the upper 7.6 cm (3 in.) of all three test pads have lower stiffnesses than the bottom 25.4 cm (10 in.). This near-surface layer exhibits a lower stiffness, presumably from lower effective stresses and possibly from some disturbance caused by the compaction equipment. Also, higher moisture contents during compaction of the base yielded lower stiffnesses, even at the same in situ density.

Original languageEnglish
Pages (from-to)95-102
Number of pages8
JournalTransportation Research Record
Issue number1673
StatePublished - 1999

ASJC Scopus subject areas

  • Civil and Structural Engineering
  • Mechanical Engineering


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