Study on the Compressive Bearing Performance and Calculation Methods for Bearing Capacity and Settlement of Pre-Bored Grouted Planted Piles Based on Field Tests

Pre-bored grouted planted pile has been increasingly applied in infrastructure construction in soft soil areas in recent years owing to its high bearing performance, low construction disturbance, and reduced slurry discharge. However, the synergistic load-bearing mechanism between the inner core pile and the surrounding cement soil is relatively complex, and the design calculation methods provided in existing studies and specifications for this pile type remain incomplete. Therefore, based on field tests, this study investigates the compressive bearing performance and load transfer behavior of pre-bored grouted planted piles, and further develops calculation methods for bearing capacity and settlement. The results show that, in this test field, due to grouting and slurry penetration reinforcement, the ultimate shaft resistance at the cement soil–soil interface is significantly improved, reaching 1.49–3.21 times the recommended values for bored cast-in-place piles in current codes. The enlarged base effectively enhances pile tip bearing capacity, while a nodular core pile near the pile base promotes the mobilization of base resistance. Furthermore, shaft resistance and base resistance models, together with their corresponding calculation methods, are established by considering both the enhancement effect of grouting on interface shaft resistance and the contribution of the enlarged pile base. Calculation methods for total bearing capacity and settlement are also summarized based on the two field test piles at this test site. The findings of this study can provide experimental support, theoretical basis and methodological reference for the bearing mechanism analysis, bearing capacity and settlement calculation, and engineering application of pre-bored grouted planted piles and similar composite pile foundations. Because the conclusions are based on only two field test piles at a single site, further validation with more field test data under different geological conditions is still needed.