Micropiles to the Rescue

An in-depth underwater inspection revealed extensive cracking and low-strength concrete within the seals of all intermediate pier foundations of the U.S. 70 bridge that crosses Lake Hamilton in Hot Springs, Arkansas. After consideration of several rehabilitation solutions, the Arkansas State Highway and Transportation Department recommended and selected a micropile rehabilitation option as the most cost-efficient way to transfer loads from the pier footing directly to the rock below, bypassing the seal concrete. Micropiles are high-capacity drilled piles, usually in the range of 5 to 12 inches in diameter, that can reach depths greater than 200 ft and achieve working loads that exceed 200 tons. In the Lake Hamilton project, the designed micropile was comprised of 7-in. diameter, 1.5-in. thick, Grade 80 steel casing; a 2-in. thick, Grade 80 reinforcement bar; and 5,000-psi non-shrink grout with a minimum embedment depth of 17 feet. A total of 152 micropiles were installed. Because of their small diameters, the micropiles could be installed through the existing foundation and grouted into place. Specialized drilling equipment enabled the easy conversion to a larger diameter casing and allowed the contractor to drill through the existing reinforced foundations and a debris layer without the hole caving in.

• Authors:
  • Sullivan, Ryan
  • Huang, Jian
  • Klevens, G Alan
• Publication Date: 2005-9

Language

• English

Media Info

• Media Type: Print
• Features: References;
• Pagination: pp 22-25
• Serial:
  • Bridges
  • Volume: 8
  • Issue Number: 5
  • Publisher: ZweigWhite

Subject/Index Terms

• TRT Terms: Bridge foundations; Bridge piers; Case studies; Cracking; Drilling; Grout; Highway bridges; Load transfer; Material reinforcement; Mechanical seals; Rehabilitation
• Uncontrolled Terms: Micropiles
• Geographic Terms: Hot Springs (Arkansas)
• Subject Areas: Bridges and other structures; Design; Highways; Maintenance and Preservation; I24: Design of Bridges and Retaining Walls; I60: Maintenance;

Filing Info

• Accession Number: 01014903
• Record Type: Publication
• Files: TRIS
• Created Date: Jan 3 2006 8:19AM