Fibre-Reinforced Grout for Micropile Construction-Article

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The study examines whether adding fibers to grout can improve the bending and lateral performance of hollow-bar micropiles, whose small cross-sections can limit their resistance to lateral loads.<br /><br />Researchers tested grout containing plastic, basalt, steel, or micro-steel fibers at dosages of 1%, 1.5%, and 2%. They measured compressive and tensile strength, elastic modulus, and flexural strength. Steel and micro-steel fibers were selected for further testing: nine 1 m-long model micropiles were subjected to pure bending, and their moment–curvature behavior was measured. The results were also used in LPile analyses. Finally, a full-scale micropile containing 1% micro-steel fibers in the upper 2.25 m was tested under lateral loading and compared with conventional-grout piles.<br /><br />Steel and micro-steel fibers improved grout tensile strength; at 2% dosage, it increased by approximately 100–110% over plain grout. Micro-steel fibers at 2% also produced the greatest gains in elastic modulus and flexural strength. In model micropiles, steel-fiber grout increased moment capacity and improved post-cracking behavior. Fiber-reinforced models were more ductile, while plain-grout models failed in a brittle manner, with grout crushing and separating from the central bar.<br /><br />LPile analyses estimated lateral-capacity increases of 12.9% for micropiles with 1% micro-steel fibers and 3.6% with 1% steel fibers. In the full-scale test, the micro-steel-fiber micropile had a stiffer response and approximately 10% greater lateral capacity than the average of three conventional-grout piles.<br /><br />Overall, fiber reinforcement—particularly micro-steel fibers—shows potential to improve micropile flexural strength, ductility, and lateral capacity.

Keywords

micropiles

fiber-reinforced grout

micro-steel fibers

steel fibers

lateral load resistance

bending performance

flexural strength

moment-curvature behavior

ductility

LPile analysis