This paper presents the soil-structure interaction, particularly negative skin friction, of the rigid inclusion columns over a 3.5-year monitoring period. In order to understand the fundamental behavior of rigid inclusions, typical deep foundation and drilled displacement pile approaches were adopted in the analyses. First, the load test results were interpreted to determine the axial capacities and moduli of the rigid inclusion columns. Then, the estimated moduli were used in conjunction with embedded strain gage data in obtaining the axial load distribution profile along the columns from the end-of-construction to post-construction periods, spanning over several years. The strain profile shows that negative skin friction and the neutral plane location progressively developed over time at every instrumented column. Based on that, the neutral plane locations appear to be at 1/2 of the column length, where a stiff clay layer is located. By matching the interpreted loads with the effective stress approach, it was found that the measured β (= K tan δ) could range from 0.6 to as high as 2.8, assuming 80% and 20% of load transfer on upper and lower soil layers, respectively. Theoretical β values were also checked against the measured β. It was found that the ratio of K/K_o arriving at these values was approximately 2.0.
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