Micropiles, also known as minipiles, are deep foundation elements constructed using high-strength, small-diameter steel casing and/or threaded bar. Capacities vary depending on the micropile size and subsurface profile. Allowable micropile capacities in excess of 1,000 tons have been achieved.
The micropile casing generally has a diameter in the range of 7 5/8″ to 24″ inches. Typically, the casing is advanced to the design depth using a drilling technique. Reinforcing steel in the form of an all-thread bar is typically inserted into the micropile casing. High-strength cement grout is then pumped into the casing. The casing may extend to the full depth or terminate above the bond zone with the reinforcing bar extending to the full depth. The finished micropile (minipile) resists compressive, uplift/tension and lateral loads and is typically load tested.
Micropiles are an effective alternative to driven piles where headroom is restricted or disturbance such as vibrations pose a concern.