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Development of Hybrid Foundation consisting of Bearing Piles and a Mat Foundation

Research Project

Project/Area Number 15560434
Research Category

Grant-in-Aid for Scientific Research (C)

Allocation TypeSingle-year Grants
Section一般
Research Field Geotechnical engineering
Research InstitutionNagaoka National College of Technology

Principal Investigator

ONOUE Atsuo  Nagaoka National College of Technology, Civil Engineering Department, Professor, 環境都市工学科, 教授 (70332004)

Co-Investigator(Kenkyū-buntansha) KOBAYASHI Masataka  Nagaoka National College of Technology, Mechanical Engineering Department, Professor, 教授 (00042755)
KONDO Toshimi  ditto, 教授 (70042786)
IBAYASHI Kou  Nagaoka National College of Technology, Civil Engineering Department, Assistant, 助手 (10321415)
FUIITA Yutaka  Shimizu Corporation, Engineering Business Division, Department of Nuclear Engineering, Manager, エンジニアリング事業本部・原子力エンジニアリング部, 主査
Project Period (FY) 2003 – 2004
Project Status Completed (Fiscal Year 2004)
Budget Amount *help
¥3,000,000 (Direct Cost: ¥3,000,000)
Fiscal Year 2004: ¥900,000 (Direct Cost: ¥900,000)
Fiscal Year 2003: ¥2,100,000 (Direct Cost: ¥2,100,000)
KeywordsBearing capacity / Shallow foundation / Hybrid foundation / Negative friction / Model test / Axial force / Weak subsoil / Shear strength / 支持杭
Research Abstract

There are several types of foundations for buildings, such as pile foundations, shallow foundations, and floating foundations. Although a shallow foundation and a floating foundation with a mat slab are usually more economical than a pile foundation, it is occasionally difficult for these foundations to secure a sufficient safety factor against a failure of soft subsoil. On the other hand, the settlement of a building supported by piles is small even if the soft subsoil is very thick. However, the pile-heads beneath the mat often slip out of the soil, and are sometimes damaged by strong seismic motions when the subsoil subsides due to consolidation.
In order to avoid these problems and reduce costs, this project develops a new hybrid foundation consisting of a small number of bearing piles and a mat foundation. Its primary functions are to simultaneously utilize the bearing capacities of both the soft subsoil beneath the mat slab and the rigid layer where the bottom tips of pile are pen … More etrated. In order to secure the subsoil reaction force against the mat foundation, the building itself must subside together with the soil. This is made possible by a "reaction control device" at the head of the pile between the pile and the mat slab.
For the first step of this project, members developed two kinds of "reaction control device". The first one is composed of three steel plates called fixed plates connected with the mat slab and two steel plates called movable plates connected with the pile head. A pre-stressed concrete (PC) bolts bind all the plates. The axial force of the bolt is, next, applied to create a large friction force between the fixed plates and the movable plates prior to on-site installation. When the load applied to a pile exceeds the maximum limit of the friction force, the pile starts to slip but keeps supporting a load equivalent to the maximum limit. The mat slab, thus, maintains contact with the soil and a constant subsoil reaction force even when the subsoil settles due to consolidation. The second one is composed of double steel piles at the connection between the mat and a pile.
One of the main issues of this foundation is the stress concentration with depth due to the negative friction from the soil to a pile. A series of small scale stress concentration tests and a large scale test were carried out in this project. The soil model of the small scale test is φ =25cm and h=33cm, and the large test scale is φ =50cm and h=100cm. The diameters of piles used are 19.6mm and 46mm, respectively. As the test and numerical analysis results, fully mobilized negative friction force acts on the piles. It was, therefore, made clear from the present study that the maximum negative friction should be taken into consideration in the design of this hybrid foundation system. Less

Report

(3 results)
  • 2004 Annual Research Report   Final Research Report Summary
  • 2003 Annual Research Report
  • Research Products

    (4 results)

All 2004 Other

All Journal Article (2 results) Publications (2 results)

  • [Journal Article] 杭とベタ基礎の併用基礎における杭に集中する地反力について2004

    • Author(s)
      小林祐輔
    • Journal Title

      第22回土木学会関東支部新潟会研究調査発表会論文集

      Pages: 101-104

    • Description
      「研究成果報告書概要(和文)」より
    • Related Report
      2004 Annual Research Report 2004 Final Research Report Summary
  • [Journal Article] Reaction Force Which Concentrate to Pile in Hybrid Foundation2004

    • Author(s)
      Yusuke Kobayashi, Atsuo Onoue, Yuta Hara, Kazuyuki Sato
    • Journal Title

      Proceedings of 22^<nd> Annual Niigata Branch Congress of Japan Society of Civil Engineering

      Pages: 101-104

    • Description
      「研究成果報告書概要(欧文)」より
    • Related Report
      2004 Final Research Report Summary
  • [Publications] 荻迫栄治, 石井清, 藤田豊, 山崎和彦, 尾上篤生, 櫻井隆喜, 中山一孝: "杭基礎と直接基礎を併用した基礎構造の杭軸力特性"第38回地盤工学研究発表会講演概要集. 1553-1554 (2003)

    • Related Report
      2003 Annual Research Report
  • [Publications] 高橋匡史, 古川武英: "複合地盤における地反力の杭への集中と杭の引き抜き抵抗との関係"長岡工業高等専門学校環境都市工学科第5回生(Ci32回生)卒業研究論文集. 1-5 (2004)

    • Related Report
      2003 Annual Research Report

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Published: 2003-04-01   Modified: 2016-04-21  

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