After the completion of construction of a deep water pier in a port there appeared to progressively be some trace of damage in its structure, and it was soon observed that the piles were deformed and cracked. In order to explore the causes that had induced these damages, a comprehensive program of observations and experiments was conducted in the field, and the following conclusions were obtained. (1) The damage of the pier structure was caused primarily by the differential settlement, and the effect of the lateral thrust of the soil was not important. (2) The differential settlement of the pier was produced mainly because of the difference of the compression of soil between the front side and the rear side of the pier. (3) There was probably some lateral deformation of soil in the early stage, but it did not develop remarkably afterward. Accordingly, a repairing project was proposed that consisted of two main remedies: (1) to install vertical piles by the nonvibrative jacking method in place of all broken and unbroken inclined-to-river raking piles and (2) to supplement long piles under the frontal platform of the pier with all the tips of piles of this part resting on the same bearing stratum. The pier was repaired according to the above-mentioned project, and since then, no problem in service has happened during a period of more than 15 years.