Calculation of foundation vertical stiffness with the piles mutual influence effect

Aims of research. Studies to determine the effect of the distance between the piles in group with vertical oscillations of pile foundations on the value of dynamic stiffness are carried out and the results obtained in full-scale tests, within the wave model and according to SP 26.13330.2012 are compared. Methods. The eigenfrequency changes of the foundation of nine piles with a diameter ( d ) with a high pile cap are calculated depending on the distances between the piles - 2 d , 3 d and 5 d . The obtained results are compared with the data obtained after a series of pulse dynamic loads performed under semi-natural conditions on foundation models. The values of the transverse wave velocities were determined directly at the test site. Results. It is found that the reduction of the distance between the piles in the bush leads to a decrease in the natural vibration frequencies of pile foundations. Reducing the distance between piles from 5 to 2 diameters of piles leads to reduce the frequency of vertical vibrations of pile foundations by 1. times. It is shown the advantage of the results of calculations in the frame-work of the wave model in comparison with the method of SP 26.13330.2012. Also shown their high coincidence with the values obtained in the course of experiments, which allows to accurately determine the amplitude-frequency characteristics of the foundations. The results determined according to SP 26.13330.2012 have significantly lower values of natural frequencies and do not fully reflect the change in the distance between the piles. The maximum discrepancy with the experimental data is 2.7 times for the vertical oscillations of the pile foundation.