Study on the value of side friction of bored pile in loess area considering the influence of length diameter ratio

Bored-in-place piles in the loess area are mostly friction piles with a large aspect ratio. In order to study the influence of length diameter ratio on the value of pile side friction in loess area, this paper studied the load-settlement characteristics, the variation of pile axial force, and pile side friction characteristics of three test piles with different length diameter ratio through indoor tests. At the same time, ABAQUS software was used to simulate the model test to verify model test results. The results all show that the side friction in the upper part of the pile gives priority to give full play to the role, and then the side friction in the lower part of the pile begins to bear the load. With the increase of length diameter ratio, the proportion of pile end resistance to load gradually decreases, and with the pile side friction reaches the limit value, the displacement gradually moves down, and the value decreases. In order to study the value of pile side friction in loess area, a single pile load transfer model was established based on the load transfer method. Through theoretical analysis and by fitting measured soil data, the hyperbolic function parameters a and b were deduced. Hyperbolic function was subsequently used to calculate the indoor experiment pile side friction done within potting soil. The error between the measured and theoretical results was less, which indicated that the hyperbolic function method could be applied to calculate the standard value of lateral friction of pile foundations in the loess area. Combined with two example projects, the pile side friction of loess-like soil and old loess was solved by using the derived hyperbolic function method. Finally, it is concluded that the recommended value of lateral friction of loess-like soil is in the range of 40–60kPa and that of old loess is in the range of 55–80kPa.These research results can provide a reference for the determination of the standard value of lateral friction resistance of bored piles in the loess area.