Determination of Micropile Connection Flexural Resistance

Micropiles are small-diameter (typically less than 12 in) drilled and grouted non-displacement piles commonly used for foundation repair, slope stabilization, earth retention, ground strengthening, and settlement reduction (FHWA 2005). In applications where vertical clearance is limited, micropiles are an especially attractive option due to their installation in short, discrete, sections. Connections between individual micropile lengths are made through the use of integral threaded couplings. This presents a concern, however, as the flexural capacity of the threaded connection under lateral load is unknown. To assess the impact of the threaded connection on micropile flexural capacity, grouted micropile sections will be tested in four-point bending at the location of the threaded connection. For comparison, flexural tests will also be conducted on grouted, bare casings. Four-point bending allows for clearance around the threaded connection for load application and also provides a constant moment region within the specimen. Comparison between bare casing and threaded connection flexural capacities will result in a ratio to be used as a quantitative adjustment for threaded connection regions when calculating flexural resistance of micropiles. As micropiles are fabricated in multiple sizes with various arrangements of threading and connection length, there are a multitude of specimen configurations that could be examined. It is anticipated that the influence of threaded connections may vary with casing diameter. This is anticipated due to the changing ratio of thread size and connection length (constant) to casing diameter (varies). The proposed research will bound the possible results by examining both small- and large-diameter casings (tentatively 5 in. and 12 in. diameter casings). Tests will be conducted for threaded connections from two different suppliers. Input from the Kansas Department of Transportation (KDOT) will be necessary to identify appropriate sizes and suppliers (identified in this document as A and B). Two (2) grouted bare casing tests and three (3) threaded connection tests will be conducted for each micropile diameter and each supplier, resulting in a total of twenty (20) flexural tests.

Language

• English

Project

• Status: Active
• Funding: $69982
• Contract Numbers:

  K-TRAN: KU-20-4

  RE-0795-01

  C2150

• Sponsor Organizations:

  Kansas Department of Transportation

  Eisenhower State Office Building
  700 SW Harrison Street
  Topeka, KS  United States  66603-3754
• Performing Organizations:

  University of Kansas Center for Research, Incorporated

  2291 Irving Hill Drive, Campus West
  Lawrence, KS  United States  66045
• Principal Investigators:

  Collins, William

• Start Date: 20190801
• Expected Completion Date: 20241231
• Actual Completion Date: 0

Subject/Index Terms

• TRT Terms: Flexural strength; Foundations; Grout; Highway bridges; Live loads; Structural connection; Support piles
• Identifier Terms: Kansas Department of Transportation
• Subject Areas: Bridges and other structures; Highways; Maintenance and Preservation;

Filing Info

• Accession Number: 01751174
• Record Type: Research project
• Source Agency: Kansas Department of Transportation
• Contract Numbers: K-TRAN: KU-20-4, RE-0795-01, C2150
• Files: RIP, STATEDOT
• Created Date: Sep 1 2020 1:57PM