Concrete expanded-plate piles (CEP piles) are novel variable-section piles that offer broader applicability, greater bearing capacity, and superior economic benefits compared to conventional straight-shaft piles. Their increasing use in construction projects underscores these advantages. While previous studies have demonstrated the favourable bearing performance of CEP monopiles, the influence of pile spacing on the performance of CEP double piles remains unexplored. This study combines laboratory-scale unitary soil tests with ANSYS Workbench 2022R1 finite element simulations to investigate the effects of pile spacing on the bearing behaviour and soil failure mechanisms of CEP double piles. An optimal pile spacing range is proposed, and the compressive bearing capacity formula is modified accordingly. These findings establish a theoretical foundation for the development of CEP double-pile and pile group foundations, thereby supporting their wider use and promotion in geotechnical engineering.