In order to explore the strengthening mechanism that the ultimate bearing capacity of single pile with cap is greater than the sum of the ultimate bearing capacities of single pile and cap foundation under the synergistic action of pile-soil-cap

two-dimensional discrete element models (DEMs) which can reflect the processes of static load test of single pile with cap

single pile only and cap foundation only in sand are established

and the rationality of the models are verified by comparing the model-predicted results with the variation laws of load-settlement curve in the laboratory model test. Based on the validated DEMs

the deformation mechanism of the sand foundation and the bearing characteristics of pile foundation are analyzed from the microscopic perspective. The results show that

in terms of the sand foundation deformation mechanism

compared with single pile and cap foundation

the foundation soil is more significantly disturbed by the single pile with cap

and the soil in a large range under the cap participates in the process of resisting the load. As for the bearing characteristics of the pile foundation

the compactness of the soil near the pile side and pile end is strengthened by the effect of the arch formation that occurs around the pile side of the single pile with cap

which improves the lateral friction resistance and the bearing capacity of pile end. As a result

the overall bearing capacity of the single pile with cap is improved. The results of DEM can provide references for the design of pile foundation with cap and the bearing capacity estimation method.