Crushed rock or unbound granular materials constitute the top layer of geomaterial compacted in a pavement. These materials are required to be compacted using compactors or rollers at a designated target density or modulus for satisfactory performance. Studying the interaction between compactors and geomaterial is important for optimising these geomaterial layers’ construction. As field compaction is time-consuming and cumbersome, the study of material behaviour at a smaller scale is necessary. This study utilises a novel setup simulating the field compaction better to study the material's behaviour and dynamic interaction between the material and the compactor during compaction. A constitutive model was developed utilizing the geometric relationship between the contact width to plastic deformation during compaction, which can be easily measured. Using Hertzian theory, the estimation of contact width allows the estimation of contact stress. The developed model shows that it can model the experimental observation with very high accuracy (R2 > 0.98). The model is then used to predict other geomaterial properties during compaction, showing their dependence on the material state.