2016 Volume 2 Issue 33 Pages 1194-1199
Most of the existing bridges with a total number of 700,000 in Japan were built in the period of high economic growth 40 ~ 50 years ago. Many of them suffered serious deterioration or damages. Seismic reinforcement for such bridges is urgently needed as a national policy. However, reinforcement methods for existing bridge foundations are being underdeveloped, and there is no well-developed method available currently. In this paper, the diagnosis and inspection method, or the needs for seismic strengthening of existing pile foundation was reviewed first. As a new seismic reinforcement technology for existing pile foundation, the composite pile method (patented, and registered in the New Technology Information System of the Japanese Ministry of Land, Infrastructure and Transport (NETIS)) by deploying ground improvement around existing pile foundation constructed in soft ground and liquefiable ground, was proposed based on the review. Different from others which are mainly focusing on improvement of lateral bearing capacity by installing additional piles or footing, the primary purpose of this method is to improve subgrade reaction at pile head, and increase the seismic resistance of the pile foundation. The feasibility of the proposed method was confirmed based on the results of large scale shaking table tests for group piles under various ground improvement conditions with Level 1 and Level 2 ground motions, such as lateral displacement and sectional force generated on the piles during shaking.