In this paper, an importance of integrating the geotechnical investigations with pile foundation design was clarified through a case study in terms of investigation, design and construction of the connecting bridge for New-Kitakyushu airport. The basic policy and concepts for geotechnical investigations and pile foundation design of the connecting bridge for New-Kitakyushu airport are introduced. The changes of geotechnical engineering profile are briefly mentioned based on the density of in-situ investigations and laboratory tests. A method used for evaluating the vertical bearing capacity of driven piles in the actual design is explained based on the geotechnical considerations. The applicability is also verified by comparing the predicted results with the results from the full-scale pile load tests, whose results derived the reduction of the safety factor for design. Finally, the significance of geotechnical investigations including in-situ and laboratory tests and full scale pile load tests were discussed in terms of the cost performance of the construction of pile foundations for supporting the connecting bridge of New-Kitakyushu airport.