Effective Foundation Input Motion for Soil-Steel Pipe Sheet Pile (SPSP) Foundation System

Abstract

An experimental investigation to evaluate the effective foundation input motion (EFIM) of a soil-steel pipe sheet pile (SPSP) foundation system under 1g conditions was carried out through scaled model testing on a shaking table. The scaled model with 20 piles interlocked together to form a circular assembly was embedded in dry cohesionless Gifu sand housed in a laminated shear box. Tips of all the piles were rigidly bolted at the bottom of the shear box while the heads were rigidly connected to a footing. Amplitude and frequency dependent EFIM at the footing level of SPSP foundation model is obtained under dynamic ground excitations. Carried out experiments encompass a range of low-to-high amplitude of lateral harmonic ground excitation, covering elastic-to-inelastic behaviour of soil. Results show that the amplitude of EFIM at the SPSP footing level and the resonant frequency of the soil-SPSP foundation system decreases with the increase in the amplitude of excitation due to the fact that the increase in the loading amplitude results in the increase in the soil strain and thus decreases the soil stiffness. Results are also obtained in the form of kinematic interaction factors (KIF). The KIF is found approximately equal to unity up to the resonant frequency of the soil-SPSP foundation system, however, decreases above the resonant frequency reflecting the filtering effect of soil-SPSP kinematic interaction. For higher amplitude of excitations, an increase in the KIF (more than unity) is observed for a considerable number of frequencies, particularly around the lower frequency region. This can be attributed to the nonlinearity induced in the soil due to the higher amplitude of excitation.