MODEL TESTS FOR BEARING BEHAVIOR OF LARGE DIAMETER AND SUPER LONG PILE GROUP IN LARGE THICKNESS LOESS SITE

Application of large-diameter long piles and super long piles in large thickness loess foundation has increased sharply. However, bearing deformation mechanism, lateral resistance and end bearing capacity of super long piles in loess foundation differ from those of the ordinary piles. Vertical compression static load tests of super long single pile and pile group are conducted respectively. The similar material is applied as filling of model test. Laws of development of load settlement, pile shaft force, lateral resistance and soil plastic zone at the end of pile under the vertical load are analysed. Test results show that load of super long single pile is mainly undertaken by lateral resistance of pile under the vertical load, which is gradually developed from top to bottom. It belongs to pure friction pile, and the failure mode of single pile is punching failure. The influence scope of plastic deformation of pile end soil is about 1.1 times of pile diameter. Compared with the single pile, the end bearing capacity of super long pile group is greatly improved, and pile shaft force attenuation depth of the pile has decreased, and lateral resistance increases gradually along the pile body. Influence scope of the pile end soil layer is about 1.25 times of diameter, which is close to the influence scope of super long single pile. Research method and results in this paper can provide reference for research on bearing characteristics of super long piles in large thickness loess foundation.