Forced vertical vibration tests were carried out in the field on 5.8 m long driven single steel pipe pile with external and internal diameter of 0.166 m and 0.154 m. Tests were conducted on single on 2 X 2 group piles under a static load (W_s) of 15 kN. The field test results include the determination of frequency-amplituderesponses and soil-pile separation length for single pile and group piles, respectively. The frequency-amplitude responses from the experimental results were compared to the theoretical predictions based on the continuumapproach analysis utilizing the soil-pile separation depth from the experimental investigation. It was noticed that the theory well anticipates the nonlinear characteristics of the frequency-amplitude responses of the soil-pile system.