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2021 Vol.37, Issue 11 Preview Page
Evaluation of the Installation Mechanism of the Micropile with the Base Expansion Structure Using a Centrifuge Model Test

원심모형실험을 활용한 선단확장형 마이크로파일의 설치 메커니즘 평가

Jae-Hyun Kim1
,
Seok-Jung Kim2
,
Jin-Tae Han3
,
Seokhyung Lee4*
김 재현1
,
김 석중2
,
한 진태3
,
이 석형4*
1Member, Assistant Prof., Dept. of Civil Engrg., The College of Art, Culture and Engrg., Kangwon National Univ.
2Member, Senior Researcher, Planning and Coordination Dept., Korea Institute of Civil Engrg. and Building Technology
3Member, Research Fellow, Dept. of Geotechnical Engineering Research, Korea Institute of Civil Engrg. and Building Technology
4Member, Post-doctoral Researcher, Dept. of Geotechnical Engineering Research, Korea Institute of Civil Engrg. and Building Technology
1정회원, 강원대학교 문화예술･공과대학 건축토목환경공학부 토목공학전공, 조교수
2정회원, 한국건설기술연구원 기획조정본부, 수석연구원
3정회원, 한국건설기술연구원 지반연구본부, 연구위원
4정회원, 한국건설기술연구원 지반연구본부, 박사후연구원
*Corresponding Author
30 November 2021. pp. 37-49
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Abstract

Micropiles are widely used in construction field to enhance bearing capacity and reduce settlement of existing foundation. It has various benefits such as low construction expense, simple installation process, and small construction equipment. Recently, new microple equipped with the base expansion structure at the end has been developed to improve the foundation bearing capacity. The improvement of load capacity can be conceptually achieved by expanding the base expansion structure when a load is applied to the micropile. However, the expansion mechanism of the base expansion structure and the improvement of load capacity of the micropile were not yet experimentally validated. Therefore, in this study, a series of centrifuge model tests was performed to evaluate the effect of the base expansion structure on the improvement of load capacity. Two types of soil, sand and weathered rock, were prepared and the loading tests were performed using the real micropile with the base expansion structure. During the tests, the earth pressures surrounding the base expansion structure were monitored. As a result, when a load of 30 kN was applied to the micropile, the increase in the ratio of the horizontal to vertical pressure increment (∆σh/∆σv) ranged from 0.4 to 0.58 in sand and ∆σh/∆σv = 0.19 in weathered rock, respectively. Therefore, it can be concluded that the increase in the horizontal earth pressure adjacent to the base expansion structure will improve the bearing capacity of the micropile.

Keywords
Base expansion type micropile
Bearing capacity
Centrifuge test
Sand
Weathered rock

마이크로파일은 기초의 지지력 증대와 침하량 저감을 위해 건설분야에서 널리 활용되는 기초이다. 본 기초는 낮은 건설비용, 단순한 시공 프로세스와 비교적 작은 장비로 시공이 가능하다는 장점이 있다. 최근 지지력을 효과적으로 증대시킬 수 있는 선단확장형 마이크로파일이 개발되었다. 본 기초는 수직하중이 재하될 때 마이크로파일 선단부에 설치된 지압구가 팽창하여 주변지반에 작용하는 수평토압을 증가시키며, 이로 인해 기초의 지지력이 향상된다. 하지만, 현재까지 지압구 확장 메커니즘과 지지력 증대효과가 실험적으로 명확히 검증되지 않았다. 따라서, 본 연구에서는 지압구의 설치효과를 검증하기 위해 원심모형실험이 수행되었다. 이를 위해, 모래지반과 풍화암으로 구성된 지반을 각각 조성하고, 실제 선단확장형 마이크로파일에 대한 하중재하실험을 수행하였으며, 기초에 수직하중이 작용할 때 지압구 주변에 설치된 토압계를 통해 지압구의 팽창거동을 관찰하였다. 실험 결과, 30kN의 하중이 기초에 작용할 때 모래지반에서는 수직토압대비 수평토압의 증가량(∆σh/∆σv)이 0.4 - 0.58의 범위를 보였으며, 풍화암지반에서는 ∆σh/∆σv = 0.19로 확인되었다. 본 결과를 통해 지압구 확장에 따른 수평토압 증가가 실험적으로 확인되었으며, 이로 인해 마이크로파일의 지지력이 증가될 것으로 판단된다.

References
1
Han, J.T., Kim, S.R, Jang, Y.E., and Lee, S.H. (2013), Evaluation of Bearing Capacity of Waveform Micropile by Numerical Analyses, Journal of Academia-Industrial Technology, Vol.14, No.11, pp.5906-5914. 10.5762/KAIS.2013.14.11.5906
2
Hwang G.C., Ahn, U.J., Lee, J.S., and Ha, I.S. (2018), A Study on the Bearing Characteristics of No-grouted and End-compressed Micropile Adopting Wedge Horizontal, Journal of The Korean Geotechnical Society, Vol.34, No.3, pp.67-75.
3
Kim, D.S., Kim, N.R., Choo, Y.W., and Cho, G.C. (2013), A Newly Developed State-of-the-art Geotechnical Centrifuge in Korea, KSCE Journal of Civil Engineering, Vol.17, No.1, pp.1-8 10.1007/s12205-013-1350-5
4
Kim, J.H., Choo, Y.W., Kim, D.J., and Kim, D.S. (2016), Miniature Cone Tip Resistance on Sand in a Centrifuge, Journal of Geotechnical and Geoenvironmental Engineering, Vol.142, No.3, 04015090. 10.1061/(ASCE)GT.1943-5606.0001425
5
Lee, S.H., Han, J.T., Jin, H.S., and Kim, S.J. (2021), 3-D Numerical Analysis for the Verification of Bearing Mechanism and Bearing Capacity Enhancement Effect on the base Expansion Micropile, Journal of The Korean Geotechnical Society, Vol.37, No.27, pp.19-31 (in Korean).
6
Lee, T.H. and Im, J.C. (2006), An Experimental Study on the Reinforcement Effect of Installed Micropiles in the Surround of Footing on Dense Sand, Journal of The Korean Geotechnical Society, Vol.22, No.5, pp.69-81 (in Korean).
7
Lo Presti, D.C.F, Berardi, R., Pedroni, S., and Crippa, V. (1993), A New Travelling Sand Pluvaitor to Reconstitute Specimens of Well Graded Silty Sands, Geotechnical Testing Journal, Vol.15, No.2, pp.18-26. 10.1520/GTJ10263J
8
Madabhushi, G. (2014), Centrifuge Modeling for Civil Engineers, CRC Press.
9
Miura, S. and Toki, S. (1982), A Sample Preparation Method and its Effect of Static and Cyclic Deformation-strength Properties of Sand, Soils and Foundations, Vol.22, No.1, pp.61-77. 10.3208/sandf1972.22.61
10
Park, S. (2018), Evaluation of uplift behavior for drilled shaft socketed into rock via centrifuge model tests, Master Thesis, Korea Advanced Institute of Science and Technology.
Information
  • Publisher :The Korean Geotechnical Society
  • Publisher(Ko) :한국지반공학회
  • Journal Title :Journal of the Korean Geotechnical Society
  • Journal Title(Ko) :한국지반공학회 논문집
  • Volume : 37
  • No :11
  • Pages :37-49
  • Received Date : 2021-09-29
  • Revised Date : 2021-11-09
  • Accepted Date : 2021-11-09
  • DOI :https://doi.org/10.7843/kgs.2021.37.11.37
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