Abstract: The liquefaction of saturated fine sand is a crucial difficulty hindering the development of long auger cement fly-ash gravel (CFG) pile construction technology. However, the relationships between liquefaction and two construction-related parameters of CFG piles, namely the pile spacing and the pipe rotation speed, during the piling process have not been well investigated. Thus, in this paper, the influences of these two parameters on the liquefaction of saturated fine sand are analyzed, and the relationships between the two parameters and liquefaction are established. Besides the theoretical studies, an experiment platform is also established to reproduce the construction process of a long auger CFG pile in the saturated fine sand. The results of laboratory tests show that the increase of pipe rotation speed and the decrease of pile spacing promote the liquefaction of saturated fine sand, shorten the pile length, and increase the pile diameter. In order to relieve the liquefaction of saturated sand, the pipe rotation speed should be reduced and the pile spacing should be increased.

Key words: long auger CFG pile, pile spacing, pipe rotation speed, saturated fine sand, excess pore water pressure