Field tests on bearing behaviors of cement mortar-expanded precast piles

The cement mortar-expanded precast pile is a new type of expanded pile technology, which improves the overall bearing performance of the expanded piles and expands the engineering application range of the precast piles through the innovation of the pre-bored grouting method and the application of the high-quality factory grouting materials. In order to reveal their vertical bearing characteristics, the studies on the bearing performance of the expanded piles under different pile top pressure modes and pre-bored conditions are carried out based on the full-scale tests. The test results show that the pressure mode at pile top has small effects on the bearing performance of the expanded precast piles, but has significant ones on the internal load transfer mechanism. Compared with that of the full-section pressure, the axial force of inner precast piles under pressure alone is relatively large, and the decay rate is faster as the depth increases. The interaction between the inner precast piles and the outer cement mortar is more obvious for the internal precast piles under compression. Furthermore, different pre-bored conditions will cause different pile end support conditions, which have significant effects on the bearing performance of the expanded piles. The bearing capacity of the super-leading hole enlargement pile (SC) is greater than that of the isotonic enlargement pile (EC) and the short-leading hole enlargement pile (LC). The failure of all the test piles under the ultimate loads is the overall subsidence, indicating that the shear capacity of the interface between the inner precast piles and the outer cement mortar is greater than the shear action between the outer cement mortar and the surrounding soil. When the strength of the outer grouting materials is greater than 15 MPa, the interface damage between the inner precast piles and the outer materials may not be considered.