<p>The accumulation structure of fragmented residual coal in the goaf undergoes ongoing deformation under long-term loading from the overlying strata. This is the vital link in the occurrence of disasters such as ground subsidence and coal spontaneous combustion (CSC). The specific linkage mechanism is that during deformation, changes in its volume and deformation resistance directly influence the extent of ground subsidence. Meanwhile, the evolution of internal void structures regulates the CSC risk by altering the seepage field (oxygen transport pathways) and temperature field (heat accumulation conditions) in the goaf. Therefore, elucidating its deformation mechanism is essential to addressing such hazards. This study integrated Weibull distribution functions, four-particle pile-up configurations, and Hertzian contact deformation principles to derive two classes of theoretical models. These models decoupled multiple basic deformation modes of coal particles inside the accumulation structure and quantified their competitive interactions. It was found that the basic deformation mode of internal coal particles, which dominated the overall deformation of the accumulation structure, was not static but dynamically switched during deformation. Specifically, the initial stage is characterized by structural deformation of internal particles; the intermediate stage transitions to secondary fragmentation-dominated behavior; and the final stage further transforms toward primary deformation-dominated mechanisms. This dynamic evolution enables a quantitative evaluation of how internal particle deformation influences the overall structural response, addressing the limitations of existing qualitative descriptions of deformation mechanisms. The proposed framework was expected to extend to the mechanical behavior of similar granular systems (e.g., ore piles, tailings dams) and to guide the optimization of goaf-filling/grouting and fire-prevention technologies.</p>