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Reliability estimates of compaction characteristics of lime-iron ore tailings (IOT) modified tropical black clay (i.e black cotton soil, BCS) for use as road construction material was carried out. A model was generated from measured laboratory test results, and then used in a FORTRAN-based first-order reliability program (FORM) to generate reliability indices (RI). Samples tested in the laboratory were subjected to index tests and British standard light (BSL) compaction test. In the midst of all the variables, specific gravity (Gs) recorded the greatest significant effect followed by sand content (Sa) and then Iron ore tailing (IOT) and Lime (Li) content on MDD. In the case of optimum moisture content (OMC), specific gravity (Gs), iron ore tailing content (IOT) and lime content (Li) has the most significant influence on OMC followed by sand content (Sa). Generally, RI values were less than 1.0 and thus fails to meet the conditions of Nordic Committee on Building Regulation (NKP) for serviceability limit state design. Stochastically, BSL compactive efforts recorded positive results but did not meet the requirement for modeling compaction characteristics of lime-IOT treated BCS as pavement sub-base material. Finally, higher compactive effort is recommended to model compaction characteristics of lime-IOT treated BCS in other to achieve more effective RI which that can be prudently examined during field compaction. [ABSTRACT FROM AUTHOR]