Abstract: To investigate the bearing characteristics and macro-meso failure mechanisms of composite foundations with end-bearing and floating deep cement mixing (DCM) columns, an FDM-DEM model is established for a comparative study. Results indicate that the ultimate bearing capacity of the end-bearing composite foundation is 18.7% higher than that of the floating type. Regarding excess pore water pressure evolution, zones of high excess pore water pressure in end-bearing foundations are concentrated in the shallow reinforced area and dissipate rapidly under the control of the top drainage boundary. Conversely, floating foundations, influenced by deep load diffusion, exhibit significant accumulation and markedly delayed dissipation of pore pressure in the underlying soft soil. Meso-scale force chain analysis reveals distinct instability mechanisms: strongly constrained by the rigid bearing layer at the pile tip, end-bearing piles suffer from buckling and breakage of strong force chains in the upper shaft due to stress concentration, leading to macroscopic structural failure at the pile tip. In contrast, force chains in floating piles remain geometrically continuous and intact, with instability primarily stemming from insufficient tip resistance inducing coordinated pile-soil settlement and overall punching failure.