@phdthesis{oai:muroran-it.repo.nii.ac.jp:00005105,
 author = {池田, 篤則 and IKEDA, Atsunori},
 month = {2016-02-15},
 note = {application/pdf, 本論文は，表層地盤の下に比較的密な砂層が存在する地盤条件を対象として，大型加圧土槽による模型実験および実大杭による原位置試験を実施し，それらの施工時と載荷時の挙動の考察に基づいて，回転貫入杭の新たな支持力評価法を構築したものである．最初に，支持層への根入れを変化させた施工実験および鉛直載荷実験を実施した．実験は模型実験および原位置試験であって，前者は模型杭(軸径76.3mm，羽根径152.6mm)を大型加圧土槽に作成した二層地盤に施工した場合，後者は実杭（ 軸径114.3mm，羽根径228.6mm） をシルト層を貫通させて細砂層に根入れさせた場合である．これらの実験を通して，回転貫入杭の支持層への根入れ効果に関する新たな知見として，①杭先端面が支持層に達する手前で杭体トルクや貫入率が変化するので，支持層への到達状況を概略知ることができること，②杭先端を支持層に根入れさせると羽根面の支持力は増加するが，杭先端面の支持力はほとんど変化しないこと等を得ている．更に，上記の大型加圧土槽を用いて，薄層の厚さを変化させた施工実験および鉛直載荷実験を実施し，③薄層の層厚を増加させると杭先端面と羽根面の荷重が増加するが，支持力に有効な層厚が存在すること，④載荷の進行に伴い杭先端部荷重に占める杭先端面および羽根面の荷重負担割合が変化することを明らかにしている．上記の特性から，杭先端面と羽根面に地盤のＮ値を同様に付与することの問題点，並びに杭先端部の極限支持力に一律の安全率を課して許容支持力を評価することの問題点を指摘できる．そこで，回転貫入杭工法においては杭先端面と羽根面を分離して評価することが重要との観点から，下記の考え方を導入した回転貫入杭の新たな支持力評価式の構築を行っている．１）極限支持力の評価については，杭先端面および羽根面について，それぞれ独自の支持力係数αb およびαw を導入する．２）長期と短期の許容支持力の算定では，杭先端面および羽根面について，それぞれ独自の支持力発揮率ξb およびξw を導入する．これらの評価式の妥当性は，杭の打ち止め深度の異なる原位置載荷試験結果と比較することで検証した．最後に，既往の回転貫入杭の原位置載荷試験結果に対して，杭先端面荷重と羽根面荷重を合わせた杭先端部荷重の計算値が実測値に概ね近似することから，本論文の評価式の適用性を確認した., This thesis presents a new method to evaluate the pile toe resistance of helical screw piles embedded into a relatively hard sand layer underlying soft material. Pile behavior observed during installation and loading has been examined through model tests in a large-scale calibration chamber (CC) and full-scale field tests in this study. Firstly, the monitoring of pile installations and the followed loading tests were conducted by changing the embedment length in a bearing layer. In the model tests, the model pile of 76.3 mm with a helical plate attached on its tip of 152.6 mm in diameter was screwed into a double-layered sand deposit in the CC. For full-scale field tests, the test pile of 114.3 mm with a helical plate of 228.6 mm in diameter was screwed into a sand layer underlying silt deposit. These experiments provide with new evidence as follows: ①During installation, both torque and penetration rate change as the pile tip closes to the bearing layer, which allows us to estimate the relative position between the pile tip and the top surface of bearing layer. ②Partial embedment of the pile tip to the bearing layer contributes to the increase of load mobilizing at the helical plate, while the load sustained by the bottom plate remains almost unchanged regardless of the embedment length. A series of model tests were also conducted by changing the thickness of bearing layer, where the afore-mentioned model pile was employed. The thickness of bearing layer influences on the pile behavior as follows: ③Both sustained load at the bottom plate and the helical plate increase as the thickness of bearing layer increases. However, the incremental rate tends to become constant suggesting the existence of optimum thickness of the layer. ④As applied load increases, the ratio of the sustained load among the total toe resistance changes between the bottom plate and the helical plate. Observed features in this study demonstrate that neither taking the same SPT-N value nor the same safety factor for allowable capacity to the bottom plate and the helical plate is rational, which is common in practice. The pile toe resistance for helical screw piles should be evaluated separately to the bottom plate and the helical plate. These considerations draw the following conclusions for constructing the new formula to calculate the toe capacity of helical screw piles: 1) For evaluating the toe bearing capacity, respective bearing coefficients (α ) are introduced to the bottom plate (α b) and the helical plate (α w). 2) For evaluating the allowable bearing capacity in long term and short term, respective coefficients of capacity mobilization (ξ ) are introduced to the bottom plate (ξ b) and the helical plate (ξ w) . Applicability of the derived formula was confirmed in comparison with the field test results executed in the different partial embedment to the bearing layer. Finally, the proposed formula obtained in this study was applied to previously conducted field loading test results of helical screw piles in various conditions. The calculated capacities comprising the resistance by the bottom plate and the helical plate show good agreement, which proves the applicability of this formula．},
 school = {室蘭工業大学, Muroran Institute of Technology},
 title = {回転貫入杭における先端部の支持力評価法に関する研究},
 year = {},
 yomi = {イケダ, アツノリ}
}