Evaluation of Bearing Capacity Enhancement Effect of Base Expansion Micropile Based on a Field Load Test

Seok-Jung Kim; Seokhyung Lee; Jin-Tae Han; Gyu-Cheol Hwang; Jeong-Seob Lee; Mintaek Yoo

doi:10.7843/kgs.2023.39.4.31

All Issue

2023 Vol.39, Issue 4 Preview Page Next Page

Evaluation of Bearing Capacity Enhancement Effect of Base Expansion Micropile Based on a Field Load Test 현장재하시험을 통한 선단확장형 마이크로파일의 지지력 증대효과 분석

30 April 2023. pp. 31-44

PDF XML

Abstract

A base expansion micropile was developed to improve the bearing capacity of the micropile, which bears a simple device installed at the pile base. Under an axial load, this base expansion structure radially expands at the pile tip and attaches itself around ground, compressing the boring wall in the construction stage. In this study, conventional and base expansion micropiles were constructed in the weathered rock where micropiles are commonly installed. Further, field load tests were conducted to verify the bearing capacity enhancement effect. From the load test results, it was revealed that the shaft resistance of base expansion micropiles was about 12% higher than that of conventional micropiles. The load transfer analysis results also showed that compared to conventional micropiles, the unit skin friction and unit end bearing of base expansion micropiles were 15.4% and 315.1% higher, respectively, in the bearing zone of the micropile.

Keywords

Bearing capacity enhancement

Base expansion structure

Field load test

Load transfer analysis

Micropile

선단확장형 마이크로파일은 시공시 강봉 선단에 확장 구조체를 설치하여, 강봉이 지중에 설치될 때 자중 등 압축하중이 작용하여 선단확장구가 팽창, 천공홀 주변 지반을 압착함으로써 선단부에서의 추가적인 마찰력 및 선단 지지력을 확보함으로써 지지력 증대효과를 유발하는 공법이다. 본 연구에서는 마이크로파일이 일반적으로 시공되는 풍화암 근입지반에 마이크로파일을 시공하고 재하시험을 수행하여 선단확장형 마이크로파일의 지지력 증대효과를 분석하였다. 정재하 시험 결과, 선단확장형 마이크로파일의 지지성능은 일반마이크로파일의 주면지지력 대비 약 12% 크게 발현됨을 확인하였다. 추가로, 하중전이분석을 통해 단위 주면지지력과 선단지지력을 비교한 결과, 최대 단위주면지지력은 일반 마이크로파일 대비 약 15.4%, 선단지지력의 경우, 약 315.1% 크게 나타나, 선단 지압구의 효과에 따라 지지력 증대효과가 발생함을 확인하였다.

References

ASTM (1994), Standard test method for piles under static axial compressive load. ASTM standard D1143-81, In Annual book of ASTM standards.

Bae, J.H., Lee, J.W., Shin, S.H., and Kim, D.W. (2020), Analysis of Vertical and Horizontal Behavior of Helical Piles in Sands Varying Helix Shapes and Locations, KSCE Journal of Civil and Environmental Engineering Research, Vol.40, No.4, pp.393-400.

Bruce, D.A. and DiMillo, A.F. (1995), A Primer on Micropiles, Civil Engineering, Vol.65, No.12, pp.51-54.

FHWA (2005), "Micropile Design and Construction", Publication No. FHWA NHI-05-039, U.S Department of Transportation, Washington, D.C.

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 the Korea Academia-Industrial cooperation Society, Vol.14, No.11, pp.5906-5914. 10.5762/KAIS.2013.14.11.5906

Hong, W.P., Cho, S.D., Choi, C.H., and Lee, C.M. (2012), Skin Friction Mobilized on Pack Micropiles Subjected to Uplift Force, Journal of the Korean Geotechnical Society, Vol.28, No.6, pp.19-29. 10.7843/kgs.2012.28.6.19

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.

Jang, Y.E. and Han, J.T. (2016), A Field Study on the Constructability and Performance Evaluation of Waveform Micropile, Journal of the Korean Geotechnical Society, Vol.32, No.10, pp.67-79. 10.7843/kgs.2016.32.10.67

Jang, Y.E., Han, J.T., Kim, J.H., Park, H.J., and Kim, S.H. (2015), Evaluation of Axial Bearing Capacity of Waveform Micropile by Centrifuge Test, Journal of the Korean Geotechnical Society, Vol.31, No.8, pp.39-49. 10.7843/kgs.2015.31.8.39

Jung, H. Y., Hwang, S. C., and Choi, Y. (2011), A Study on Perimeter Load Transfer Fuctions of the Large Diameter Drilled Shafts Depending on Soil Types During the Static Pile Load Tests, KSCE Journal of Civil and Environmental Engineering Research, Vol.31, No.5C, pp.163-170.

KGS (2018), Commentary on Standard Guideline for the Design of Foundation Structures, Korean Geotechnical Society.

Kim, J.H., Kim, S.J., Han, J.T., and Lee, S.H. (2021), Evaluation of the Installation Mechanism of the Micropile with the Base Expansion Structure Using a Centrifuge Model Test, Journal of the Korean Geotechnical Society, Vol.37, No.11, pp.37-49.

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.

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.2, pp.19-31.

Lee, S.H., Kim, S.J., Han, J.T., Jin, H.S., Hwang, G.C., and Lee, J.S. (2022), Three-Dimensional Numerical Analysis for Verifying Behavioral Mechanism and Bearing Capacity Enhancement Effect According to Tip Elements, Journal of the Korean Geotechnical Society, Vol.38, No.9, pp.53-67.

Information

Publisher :The Korean Geotechnical Society
Publisher(Ko) :한국지반공학회
Journal Title :Journal of the Korean Geotechnical Society
Journal Title(Ko) :한국지반공학회 논문집
Volume : 39
No :4
Pages :31-44
Received Date : 2023-03-14
Revised Date : 2023-03-21
Accepted Date : 2023-03-23
DOI :https://doi.org/10.7843/kgs.2023.39.4.31

Journal of the Korean Geotechnical Society ISSN:1229-2427(Print) 2288-646X(Online) 한국지반공학회 논문집

All Issue