Micropile casing generally has a diameter in the range of 3 to 10 inches.

Micropiles can be used for new construction, remediation or enhancement. Micropiles are rapidly gaining in popularity for use in urban areas, locations with low headroom and in other places where larger machinery cannot be used. They are an ideal alternative for underpinning and emergency repairs since they’re well suited for the most difficult natural or artificial ground conditions with little to no vibration or disturbance to existing structures.

Process:

Typically, the casing is advanced to the design depth using a drilling technique. Reinforcing steel, typically an all-thread bar is inserted into the casing. High-strength cement grout is then pumped into the casing. The casing may extend to the full depth or end above the bond zone with the reinforcing bar extending to the full depth.

This technique has been used to support most types of structures. Micropile drill rigs allow installation in restricted access and low headroom interiors, allowing facility upgrades with minimal disruption to normal operations.

Advantages
Resists compressive, uplift/tension, and lateral loads
Comprehensive fleet of rigs and tooling for difficult subsurface conditions and limited access
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
The finished micropile (mini pile) resists compressive, uplift/tension, and lateral loads and is typically load tested following ASTM D 1143 (compressive), ASTM D 3689 (uplift/tension), and ASTM D 3966 (lateral). Capacities vary depending on the micropile size and subsurface profile. Allowable compressive capacities of more than 500 tons have been achieved