Suitability and Bearing Behavior of PHC Pipe Piles in Underlying Mudstone

Prestressed High-Strength Concrete (PHC) pipe piles are extensively utilized in pile foundation projects due to their exceptional strength, excellent load-bearing capacity, and strong penetration capabilities. This study investigates the suitability and load-bearing characteristics of PHC pipe piles in underlying mudstone strata through field load tests and finite difference method (FDM) numerical modeling. Results indicate that: (1) Field tests demonstrate that PHC piles transition from end-bearing friction piles to friction end-bearing piles with the increase of pile head load, exhibiting excellent elastic deformation properties with minimal compression in the mudstone bearing layer. FDM numerical modeling reveals that when the load reaches 5700 kN, the tip resistance increases sharply from 53 to 94%, indicating that shear failure occurs at the pile-soil interface. However, the structural integrity is maintained through complete load redistribution to the pile tip, validating the strong end-bearing capacity of PHC piles in mudstone. (2) The FDM was further used to analyze the soil stress below the pile tip. It was found that after the failure of side friction resistance, the mudstone bearing layer undergoes plastic deformation, resulting in the formation of a strain-softening zone characterized by an ellipsoidal stress bulb beneath the pile tip. This mechanism significantly reduces instantaneous settlement during loading, thereby enhancing foundation stability and safety. The findings of this study demonstrate the suitability and advantages of PHC piles in mudstone sites for efficient load-bearing. These results can serve as a reference for foundation reinforcement and the design of PHC piles under similar geological conditions.