The location of flexible anchorage of quaywall is set with reference to K.Kubo's experimental studies in the Technical Standards for Port and Harbour Facilities.
　But K. Kubo's experiments were made only on piles on surface ground, but not on ones under ground.
　Noticing this point, the behavior of flexible anchorage under ground has been observed by model test of quaywall.
　The results are as follows:
1. The characteristics of piles under ground are basically the same as those of piles on surface ground. But the influence of the overburden is significant.
2. In a comparison of the result of the experiments with the proposal method, effective length is more likely to be 5 times of characteristic length than 3 times.
　Through the above investigation, the proposal method has been proved to be much more applicable than those which have been traditionally used.