Location

Arlington, Virginia

Session Start Date

8-11-2008

Session End Date

8-16-2008

Abstract

The foundation of two bridges was retrofitted using micropiles. The micropiles consisted of hollow core bars installed under limited headroom conditions. Of the total number of micropiles, 180 were installed in submerged sand and 80 were installed in stiff, silty clay. The micropiles were drilled using a lean cement grout which was re-circulated for de-sanding and re-use. Final grout was injected upon completion of drilling to the design tip elevation. The micropiles were subject to a rigorous quality control that included grout quality testing and proof-testing of each production micropile. All production micropiles were proof-tested up to 150 percent of the design load. In addition, four verification tests were performed on sacrificial micropiles to at least two and a half times the design load or to failure. This paper presents a description of the procedure for installation and quality control of the micropiles, and the results of the verification and proof tests performed for this project. It also provides estimated of bond strength for hollow core bar micropiles in soils similar to those encountered at the project sites. This work shows that hollow core bar micropiles provide a significant unit bond capacity in both granular and fine soils, which may be greater than that typically expected in pressure-grouted (Type B) micropiles in granular soils.

Department(s)

Civil, Architectural and Environmental Engineering

Appears In

International Conference on Case Histories in Geotechnical Engineering

Meeting Name

Sixth Conference

Publisher

Missouri University of Science and Technology

Publication Date

8-11-2008

Document Version

Final Version

Rights

© 2008 Missouri University of Science and Technology, All rights reserved.

Document Type

Article - Conference proceedings

File Type

text

Language

English

Share

 
COinS
 
Aug 11th, 12:00 AM Aug 16th, 12:00 AM

Bond Strength of Hollow-Core Bar Micropiles

Arlington, Virginia

The foundation of two bridges was retrofitted using micropiles. The micropiles consisted of hollow core bars installed under limited headroom conditions. Of the total number of micropiles, 180 were installed in submerged sand and 80 were installed in stiff, silty clay. The micropiles were drilled using a lean cement grout which was re-circulated for de-sanding and re-use. Final grout was injected upon completion of drilling to the design tip elevation. The micropiles were subject to a rigorous quality control that included grout quality testing and proof-testing of each production micropile. All production micropiles were proof-tested up to 150 percent of the design load. In addition, four verification tests were performed on sacrificial micropiles to at least two and a half times the design load or to failure. This paper presents a description of the procedure for installation and quality control of the micropiles, and the results of the verification and proof tests performed for this project. It also provides estimated of bond strength for hollow core bar micropiles in soils similar to those encountered at the project sites. This work shows that hollow core bar micropiles provide a significant unit bond capacity in both granular and fine soils, which may be greater than that typically expected in pressure-grouted (Type B) micropiles in granular soils.