Full-scale experimental study on load-deformation characteristics of prebored grouted planted piles in soft ground

Prebored grouted planted piles can effectively utilize strengthes of precast pile shafts. To clarify the influence of different construction techniques on the load transfer mechanism of composite piles, this study conducted full-scale static load tests on auxiliary-driven and gravity-driven piles. Using fiber optic monitoring technology, the study analyzes load transfer characteristics of composite piles and revealed the bearing capacity development mechanisms associated with each construction technique. The test results indicate that both construction techniques can effectively utilize strength of precast pile shafts. Among them, gravity-driven piles exhibit pure friction pile characteristics, with the side friction resistance being 1.68~3.61 times the recommended ultimate value from the cast-in-place pile geotechnical investigation, and the relative pile-soil displacement required to develop the ultimate side friction is about 10~20mm. Auxiliary-driven piles exhibit end-bearing friction pile characteristics, with the pile end resistance approximately 1.5 times the recommended ultimate value from the cast-in-place pile geotechnical investigation, and the side friction resistance of most soil layers ranging from about 1.16 to 2.5 times the recommended ultimate value. The relative pile-soil displacement required to develop the ultimate side friction is about 6.5~10mm. Simultaneously, the reinforcement mechanisms of the two construction techniques are analyzed. Gravity-driven piles reinforce the soil around the pile through penetration by significantly improving the side friction resistance. Auxiliary-driven piles, due to the squeezing and expanding effect at the pile end, effectively increase the side friction resistance and pile end resistance of the composite piles. Within the test range, reducing the water-cement ratio properly can further enhance the bearing capacity of auxiliary pile-driven piles.