Kohji Koyamada

Field Investigation and Analysis Study of Damaged Pile Foundation during the 2003 Tokachi-Oki Earthquake

Konan junior high school in Hokkaido, the northernmost main island of Japan, suffered severe damage to its superstructure and pile foundations during the Tokachi-oki Earthquake (M=8.0), on September 26, 2003. The objective of this study is to verify the main factors causing this damage by field investigations and earthquake response analyses. Detailed field surveys were carried out on the superstructure and pile foundations immediately after the quake. Analyses of the structure of the pile foundation were conducted using a numerical model taking into account the effect of soil nonlinearity. Strong motions observed near the school were employed as the input motion to the analysis model. It is found that compression failures at the pile heads were caused not only by the inertial force from its superstructure but also by large displacement of a very soft clay, leading to differential settlement as well as shear cracks in walls of the superstructure.