Table 4 Impact factor fitting curve of pile-soil relative displacement impact factor.

0.15 m

\(F_{o} = - 0.09727x + 0.00458x^{2} - 7.7616 \times 10^{ - 5} x^{3} + 4.2989 \times 10^{ - 7} x^{4} + 0.99599\)

0.75 m

\(F_{o} = - 0.09753x + 0.00448x^{2} - 7.68842 \times 10^{ - 5} x^{3} + 4.33416 \times 10^{ - 7} x^{4} + 0.99545\)

1.35 m

\(F_{o} = - 0.09341x + 0.00439x^{2} - 7.2878 \times 10^{ - 5} x^{3} + 3.91162 \times 10^{ - 7} x^{4} + 0.99555\)

1.95 m

\(F_{o} = - 0.09704x + 0.005x^{2} - 8.83981 \times 10^{ - 5} x^{3} + 5.01323 \times 10^{ - 7} x^{4} + 0.99702\)

2.7 m

\(F_{o} = - 0.09841x + 0.00495x^{2} - 8.68691 \times 10^{ - 5} x^{3} + 4.90157 \times 10^{ - 7} x^{4} + 0.9966\)