EFFECTS OF LONGITUDINAL AND TRANSVERSE PILE SPACING ON THE DYNAMIC IMPEDANCE OF PILED RAFT FOUNDATION

Soil–structure interaction is crucial for evaluating the seismic response of structures. The dynamic impedance of a piled raft foundation depends on the dynamic interaction between the raft and the pile group. This paper presents a simple method for calculating the dynamic impedance of piled raft foundations with different pile spacing ratios in two directions, subjected to dynamic horizontal and rotational loads. Parametric analysis is useful for estimating system performance by varying design parameter inputs. Numerical analyses were conducted, and the obtained dynamic interactions were used to analyze frequency characteristics of the dynamic interaction factors between the raft and the pile group, which are essential for simplified calculations. The analysis revealed that, although the frequency characteristics of the dynamic interaction factor vary with the pile spacing ratio, a clear trend emerges when the pile spacing is evaluated using the geometric mean of the two directions. Furthermore, by expressing the frequency characteristics of this dynamic interaction factor as an arbitrary function, we developed a method for simplified calculation of the dynamic impedance of piled raft foundations, even when the pile spacing ratio varies. The method was calibrated for the numerical conditions investigated. The method showed good agreement within the investigated parameter range, and discrepancies increased at high frequencies. For the horizontal and rotational dynamic impedance of piled rafts within the investigated parameter range, the mean absolute percentage error for the real part was 14 %, and that for the imaginary part was 5 %.