Field tests on bearing capacity of digging-hole pile for transmission lines under complex loads

In order to study the bearing performance and difference of the foundation for transmission lines under complex load-bearing situations, by taking the digging-hole piles commonly used in transmission-line projects as the object and selecting the typical loess area as the test site, the field tests on the bearing performance of digging-hole piles for transmission lines under four loading cases are carried out. By testing the displacements of pile top and the soil pressures at pile end, the load-displacement curves, the ultimate bearing capacities and the soil pressures at pile end of digging-hole piles under different loading conditions are analyzed. The results show that due to the differences of bearing mechanism and failure mode, the morphological characteristics of load-vertical displacement curve of digging-hole piles under different vertical loads are obviously different, which is shown as "steep drop" under uplift loads and "slow change" under compression loads. For the digging-hole piles under combined loads, the compression force improves the horizontal bearing capacity, on the contrary, the uplift force weakens the horizontal bearing capacity. The relationship between the soil pressure at pile end and the compression load can be expressed by the quadratic function. Due to the different deformation characteristics of different types of piles under horizontal loads, the eccentric effects of the soil pressure at the end of the rigid piles are obvious, and those of the elastic piles are not obvious.