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This study evaluates the potential use of bottom ash (BA) in the subbase layer of pavements. Lateritic soil, a conventional subbase soil, was mixed with 0–60% of BA, and their properties were studied. The lateritic soil was sieved into grade B and grade D soils. Each grade of soil is mixed with BA at varying content and their bearing capacity and permeability properties were tested. The California bearing ratio (CBR) samples were compacted at optimum water content (OWC) and OWC + 2%. At OWC, both grades of soil showed a high CBR when 30–60% BA was mixed. However, when the samples were compacted at OWC + 2%, CBR values reduced drastically and only a few mixtures passed the minimum CBR requirement for subbases by the Department of Highway, Thailand. To explain the mechanism behind the CBR trends, the gradation of the mixtures before and after CBR was checked and interaction compaction effects were observed. This phenomenon was further proved by the results of permeability. [ABSTRACT FROM AUTHOR]