Macropiles, ultra-high-capacity micropiles, are deep foundation elements constructed using steel pipe. Typically, the pipe is advanced using a drilling technique to the design depth. In cases where the drill hole remains open without casing, an open hole can be advanced to the bearing depth and the pipe subsequently installed. Reinforcing steel in the form of all-thread bar or concentric pipes is inserted into the pipe. High-strength cement grout is then pumped into the pipe or pipes by tremie. The pipe may terminate above the bond zone with the reinforcing steel extending full depth. The finished foundation element resists compressive, uplift and lateral loads. The technique has been used to support buildings and bridges.
Source: Hayward Baker