@phdthesis{oai:muroran-it.repo.nii.ac.jp:00008939,
 author = {中沢, 楓太 and NAKAZAWA, Futa},
 month = {2016-06-08},
 note = {application/pdf, 本論文は，実地盤でも一般的な地層構成である表層の緩い砂層の下に比較的密な砂層が存在する地盤条件を加圧土槽（直径1,000mm，高さ1,200mm）に作製し，回転貫入杭（軸径d0=48.6mm，羽根径dw=97.2mm）の施工から引抜き載荷までの一連の挙動に関する模型実験を実施し，杭体各部（羽根面，杭先端面および杭周面）の抵抗力特性を明らかにした後，回転貫入杭の引抜き抵抗力に関する実用的な評価方法を提示したものである。回転貫入実験では，杭先端面が支持層に近づくと杭の貫入率が低下するが，羽根面が支持層に達した時点からの貫入率はほぼ一定になること，杭頭部の回転トルクは杭先端面の抵抗力や羽根面の推進力を反映させており，施工管理の指標になることを明らかにした。それに引続く引抜き載荷実験で得られた主な知見は以下の通りである。① 杭頭部の引抜き荷重Pは羽根径dwの5～10％引抜き時に最大となり，その後は減少もしくは一定に推移する傾向を示し，押込み荷重が作用する既往の研究における回転貫入杭の挙動とは大きく異なる。② 杭先端面が支持層に近づくことで羽根上部の砂層がより密な状態になるため，羽根面の引抜き抵抗力Rwは支持層へ根入れさせない場合でも増大する。③ 杭先端面の引抜き抵抗力Rbは，羽根径dwの0.5％程度の小さな引抜き量で最大となり，支持層への根入れ長さにかかわらず概ね一定となる。④ 羽根面の抵抗力Rwが減少を始める羽根径dwの5～10％引抜き時になると杭周面の引抜き抵抗力Rsが増大して，抜け上がりに伴う杭体抵抗力の減少を補う働きを示す。　次に，上記の引抜き抵抗力特性に基づいて，a）施工時情報（杭頭部の回転トルクT），b）羽根近傍地盤のせん断破壊面，c）地盤のN値を利用する3種類の手法について，杭体各部の引抜き抵抗力の評価方法を検討した。実用的な観点から考察すると，羽根面抵抗力Rwと杭先端面抵抗力Rbを加算した杭先端部の引抜き抵抗力Rpが地盤のN値との相関性が高いことから，本論文では回転貫入杭の極限引抜き抵抗力Rup（kN）を算定する下式を提示した。Rup= (159･ +264) Awここで，　Aw（m2）：羽根面積=π(dw 2 ―d0 2)/ 4：羽根面の上方3dwから杭先端面の下方3d0区間の平均N値最後に，上記の算定式と原位置載荷試験結果を比較し，算定精度を更に向上させるための今後の課題を指摘した。, In this thesis, a series of model tests for the helical screw pile with a pile diameter d0 of 48.6mm and diameter of the helical plate dw of 97.2 mm are conducted to investigate pile behaviors during installation and uplift loading in a large-scale calibration chamber. Based on pulling resistance characteristics of three component parts (e.g. the helical plate, the bottom plate and the pile shaft), a formula is proposed to practically evaluate the pulling resistance of the helical screw pile embedded in a relatively dense sand layer underlying loose sand. The installation test results show that the penetration rate decreases as the bottom plate closes to the bearing layer, and then keeps constant after the helical plate reaches the bearing layer. Therefore, the resistance of the bottom plate and the driving force of the helical plate can be estimated by the torque of the pile head.The following findings have been obtained from pulling load tests:① the maximum pulling load of the pile head P is located on the uplift displacement equal to 5~10% of the diameter of the helical plate dw and then it gradually decreases or reaches constant condition. The tendency is different from the compressive load test result of previous researches.② when the bottom plate closes to the surface of the bearing layer regardless of entering the bearing layer, the pulling resistance of the helical plate Rw increases against changes of compaction of the sand layer above the helical plate. ③ without considering the length of pile entering the bearing layer, the pulling resistance of the bottom plate Rb reaches the maximum value at a uplift displacement of 0.5% of the diameter of the helical plate.④ the pulling resistance of the helical plate Rw begins to decease on a uplift displacement equal to 5~10% of the diameter of the helical plate dw, while the pulling resistance of the pile shaft Rs increases simultaneously. Accordingly, the decrease of the pulling resistance of the pile is compensated during the slip-up process. Besides, on account of the above-mentioned test results, evaluation methods for three component parts of the helical screw pile are discussed by considering three cases, that is, a) the information of construction (such as the torque of the pile head T), b) the shear fracture plane of ground surrounding to the helical plate, and c) the SPT-N value of ground. From the practical view, the pulling resistance of the pile toe Rp, which is sum of the pulling resistance of the helical plate Rw and the pulling resistance of the bottom plate Rb, has closely relationships with the SPT-N value of ground. Therefore, this thesis proposes a formula for calculating the ultimate pulling resistance Rup (kN) as follow:  Rup= (159･ +264) Awwhere, Aw (m2): the area of the helical plate=π(dw2-do2)/4, and is the average SPT-N value of grounds from upside of treble height of diameter of the helical plate (3dw) to downside of treble depth of the pile diameter (3d0). It should be noted that comparing with in-site loading test results, it is necessary to improve the precision of the above formula as a future work.},
 school = {室蘭工業大学, Muroran Institute of Technology},
 title = {回転貫入杭の引抜き抵抗力特性に関する実験的研究},
 year = {},
 yomi = {ナカザワ, フウタ}
}