The RTRI has experienced cases where RC piles judged to be damaged under the current evaluating method after being subjected to an earthquake were found to actually be intact. To investigate the cause of these discrepancies, the RTRI performed [1] a compression test on an RC pile specimen and [2] a loading test on a ground versus RC pile system, both under different values of constraining pressure. The results showed that the strength and deformation characteristics of RC piles were improved by the effects of the concrete being constrained by a ground pressure similar to that of normal RC members, in addition to the strengthening effects of hoop ties (Fig. 2). This was a result of the piles being buried and being exposed to the constraining pressure of the surrounding ground (Fig. 1). The RTRI also confirmed that the effects of damage to RC piles was mitigated, being spread over a wide area rather than being concentrated at a single point.Based on the mechanism outlined above, the RTRI proposed a method of evaluating the deformation characteristics of RC piles by introducing the effects of the ground's constraining pressure (Fig. 3). This method converts the pressure acting on the concrete from the ground into that from hoop ties to evaluate the deformation characteristics. The RTRI compared the measurement and test results to verify the validity of the method, demonstrating that the deformation characteristics improved by about 10% resulting in decreased manufacturing costs. The study results have been incorporated into a new earthquake-resistant design standard that has been under review since 2005 and will be applied to actual fieldwork.
   The study was performed with a subsidy from the Ministry of Land, Infrastructure and Transport.