羽根付き鋼管杭の水平載荷実験による杭周水平地盤抵抗に関する研究

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  • STUDY ON LATERAL SOIL RESISTANCE AROUND STEEL PIPE PILE WITH WINGS BY STATIC CYCLIC LOADING TESTS
  • ハネツキキ コウカン クイ ノ スイヘイサイカ ジッケン ニ ヨル クイシュウ スイヘイ ジバン テイコウ ニ カンスル ケンキュウ

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<p> 1. Introduction</p><p> Many types of steel pipe piles with steel spiral or flat wings welded to the pile tip or pile shaft have been developed and put to practical use. Piles with wings are generally driven into the ground by giving torque to the pile shaft during installation. Compared to cast-in-place concrete piles and embedded piles, piles with wings can reduce construction by-products because waste soil reduces. Recently, diffusion of piles with large wings has expanded the range of applications to large buildings. However, the wings that has diameter larger than the pile diameter are known to loosen soil around the pile shaft. The loosened soil may affect the lateral subgrade reaction of the pile. In this study, a cyclic lateral loading test was conducted on a pile with two flat plate-shaped wings in order to understand the following properties for lateral resistance. 1) Effect of the presence or absence of wings, 2) Effect of differences in wing diameter ratio, 3) Effect of aging after installation, 4) Grasp the secant stiffness and hysteresis damping of the steel pipe pile with wings subgrade reaction.</p><p> 2. Method</p><p> This experiment was conducted in Ibaraki Prefecture. The soil deposit at the test site consisted of weak volcanic ash soil. From the ground surface to 0.55 m below ground level (GL) is andosol, from GL-0.55m to GL-2.2m is weathered volcanic ash, from GL-2.2m to GL-3.2m is volcanic ash, and beyond GL-3.2m is sand. Four types of piles were tested. For the test pile, a JIS G 3444 general structural carbon steel (STK) pipe of outer diameter φ 267.4 mm × material thickness t 9.3 mm (steel grade 490) was used. The pile with wings was fabricated by welding two flat plates to the tip of the steel pipe while preparing the edge such that the inclination angle of each wing became 10°. The test piles had a shaft length of 5 m. To measure the bending strain of the pile, strain gauges were attached on the inner surface of the pile. The loading device consisted of a test pile, reaction pile, and hydraulic jack. For the reaction force, the pile heads of these four reaction piles were combined in a square form with H-shaped steel. Test piles are allowed free rotation of the pile head. The lateral displacement of the test pile was measured at two points: the load height and GL+100 mm. The lateral displacement at the position of at GL+100 mm is referred to as "reference displacement". The experiment controlled by reference displacement.</p><p> 3. Conclusions</p><p> The major findings obtained from this study are summarized as follows:</p><p> (1) The lateral resistance of the pile with wings was smaller than that of the pile without wings because of loosening soil around pile by the wings passing.</p><p> (2) The difference in wing diameter between 2.3Dp and 3.0Dp had little effect on the lateral resistance of the piles. It is considered that the peeling depth has a more dominant influence than the passing region of wings as a factor.</p><p> (3) Even one year after construction, the loosened soil around the pile with wings affected its lateral resistance.</p><p> (4) The secant stiffness of the piles with wings was smaller than that of the pile without wings. Secant stiffness ratio of those piles became larger depending on the pile displacement and was influenced by ground depth and soil type. The hysteresis damping of the pile with wings had little influence by the pile displacement and soil type.</p>

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