Landfills are dumped without any compaction and thus have a relatively open structure, which induces high compressibility and structure degradation of the lumpy soil in the upper layer. In this study, the structure transition of lumpy material was evaluated using the intrinsic line concept. The evolution of the inter-lump porosity of fresh lumpy soils was also analysed within the homogenization framework. The compression data for a fresh lumpy soil lie initially above the intrinsic line owing to the closure of the inter-lump voids within a low stress range. Later, the compressibility decreases with the consolidation stress and the soil behaves similarly to an overconsolidated soil. Finally, the loading reaches the preconsolidation stress of the lumps, and the whole soil volume becomes normally consolidated. A dry lumpy soil in flooded condition behaves similarly; however, all the test data lie above (or on) the intrinsic line beyond the yield stress. A natural soil with metastable structure behaves in the opposite fashion: all the data lie below (or on) the intrinsic line. Finally, the structural transition of clayfills in the field as a result of weathering factors is discussed.