Micropiles, also known as minipiles, pin piles, needle piles, and root piles, are a deep foundation element constructed using high-strength, small-diameter steel casing and/or threaded bars.

Keller rig installing micropiles

Common uses

Provide structural support to most structures
Underpin foundations
Enhance mass stability
Transfer loads

Process

The casing, with a diameter generally in the range of 100 to 250 mm is advanced to the design depth using a drilling technique.

Reinforcing steel, typically an all-thread bar, is inserted into the micropile casing and high-strength cement grout pumped in. The casing may extend to the full depth or end above the bond zone with the reinforcing bar extending to the full depth.

Capacities vary depending on the micropile size and subsurface profile but compressive capacities of more than 500 tons have been achieved.

Advantages

Resists compressive, uplift/tension, and lateral loads
Can be installed in restricted access and low headroom sites with minimal disruption to operations
May avoid utility re-routing
Alleviates quality assurance concerns associated with cast-in-place piling in weak soils
Can be combined with other techniques to meet unique or complex project requirements cost-effectively and efficiently

Quality assurance

Keller has vast load test experience in various rock formations and the ability to design in-house based on various subsurface conditions.