What is a Micropile?
A Micropile (or Minipile) is a small-diameter (typically 3 to 12 inches), drilled and grouted friction pile. They are constructed using a high-strength steel casing and/or threaded rebar, surrounded by high-strength cement grout.
Despite their small size, micropiles can safely support working loads in excess of 200 tons. They are the go-to solution when massive driven pipe piles or H-piles cannot be used due to low headroom, vibration concerns, or extreme soil conditions.
1. Common Applications
Micropiles excel in environments where traditional heavy piling equipment simply cannot operate.
Underpinning
Reinforcing the existing failing foundations of historic or settling buildings with zero vibration.
Restricted Access
Drilling inside basements, under bridges, or in dense urban alleys where large rigs cannot fit.
Seismic Retrofitting
Adding tension and compression capacity to existing structures in earthquake-prone zones.
Karst/Rocky Terrain
Drilling directly through boulders, debris, and karst geology that would severely damage driven piles.
2. Micropile Steel Specifications
Because micropiles rely on a smaller surface area, the steel casing used must have exceptionally high yield strengths—often sourced from the oil & gas industry.
- High-Strength Grades: Standard A252 (35k-45k yield) is rarely used. Instead, micropiles rely on API 5CT N80 (80,000 psi yield) or P110 (110,000 psi yield) casing.
- Threaded Connections: To avoid time-consuming field welding in tight spaces, micropile casing is often supplied with flush-joint threaded ends (machined directly into the pipe wall) for fast, seamless makeup.
- Common Sizes: 4.500", 5.500", 7.000", and 9.625" Outside Diameters.
Micropile FAQ
Common engineering and installation questions.
DEEP FOUNDATIONS
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