Research on the load transfer mechanism and bearing capacity of grouted steel pipe composite piles in moderately weathered mudstone strata is insufficient.Based on a port project in Peru,this study investigates the bearing performance of composite piles in moderately weathered mudstone strata through axial compression static load tests on the composite piles.The results indicate that:1) The theoretical calculated ultimate axial compressive bearing capacity of a single composite pile is no less than 23,000 kN.In comparison with the maximum axial compressive bearing capacity of 18,000 kN of test piles,the safety factor is not lower than 1.28.2)Mobilized shaft friction resistance of moderately weathered mudstone inside steel pipe piles is no less than 258.10 kPa,with further values exceeding 270.45 and 1,845.65 kPa observed for cast-in-place piles under both mobilized shaft friction resistance and pile end bearing resistance.3)Axial force within the pile diminishes incrementally with increased embedded depth,exhibiting reduced attenuation in the steel pipe section relative to the cast-in-place section.Pile end bearing resistance approaches 0 kN when test loads are below 14,000 kN.However,it progressively develops as load increases beyond this threshold.4)When the pile-soil relative displacement exceeds 14.37 mm,the growth rate of pile end bearing resistance of moderately weathered mudstone piles decreases,but it still does not reach its peak value.The research results can provide reference for engineering practices under similar geological conditions.