本研究は回転貫入杭の引抜き方向の短期許容支持力式に関する基礎資料を得ることを目的として、杭頭荷重を有する（初期荷重ゼロ、2kN、 4kNの3種類）回転貫入杭を対象にして鉛直交番載荷試験を行ったものである。これにより交番載荷時の回転貫入杭の引抜き抵抗に対する初期荷重の影響について明らかにすることができた。本実験で得られた主な項目は以下のとおりである。%This study is designed to examine the effect of the initial load on the reciprocal load by conducting various static axial reciprocal load tests of the screwed steel pipe pile with a pile head load applied to it and obtain basic data for use in the verification of the validity of the short-term allowable bearing capacity formula which was determined in the monotonous load test. The results obtained from this study are as follows. ①The smaller is the value of the initial load, the larger is the value of the second limit resistance in the pulling direction of the ground. ②The second limit resistance in the pulling direction measured in the reciprocal load test is lower than the value measured in the monotonous load test for each test specimen.
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