Abstract: In order to solve the engineering problems such as insufficient lateral restraining capacity of the soil body and the susceptibility to spreading and bulging damage at the top of the pile when the rubble type bulk piles were reinforcing the soft ground foundation, the composite foundation technology of waste tyre grillage ring-restrained piles was proposed. By considering the changes of reinforcement type, pile diameter and bedding form, single-pile and composite foundation bearing tests were carried out, and the load-displacement curves were tested; based on different damage modes, the calculation method of single-pile bearing capacity of bulk piles was proposed and verified for accuracy. The results showed that: compared with ordinary bulk piles that reach the ultimate damage state under small displacement conditions, the ultimate bearing capacity of ring-restrained piles was obviously improved; compared with the geogrid ring-restrained piles, the load-displacement curves of tyre grid-restrained piles did not show any obvious damage points, which indicated that their radial restraining capacity was stronger; comparing with the load-displacement curves of ring-restrained piles under different pile radius conditions, it indicated that increasing the pile diameter was very effective in improving the bearing capacity of the piles. Comparing the load-displacement curves of piles with different pile diameters, it was indicated that increasing the pile diameter appropriately had a significant effect on increasing the pile bearing capacity, and the setting of gravel bedding further improved the pile bearing capacity. The study results had important engineering application value for the promotion of this type of pile foundation and the improvement of recycling of solid waste resources.

Key words: waste tire grids, circular constraint loose pile, composite foundation reinforcement, load-displacement curve, ultimate bearing capacity