Micropiles are small diameter drilled and grouted piles reinforced with a high-strength threaded bar to transfer loads to a competent soil or rock layer. Typically, micropiles are classified as 2.5″ to 12″ in diameter and due to the small pile size are often installed with permanent steel casing to provide increased lateral capacity.
A micropile is a frictional foundation element developing capacity through the bond between the cement grout column and the surrounding soil/rock which provides both tension and compression resistance. Micropile capacities vary depending on the micropile drill diameter, reinforcing size and soil conditions in combination with the installation and grouting procedure. The design adhesion between the grout and soil can be increased using installation and grouting techniques.
Micropiles can be installed using air or mud rotary drilling, impact driving, jacking, vibrating or augering machinery. The wide range of micropile drill tooling available allows flexibility to drill in many ground conditions from soft clays to hard bedrock.
Advantages of micropiles:
- High load capacity in both tension and compression
- Easily socketed into hard rock and can penetrate through subsurface obstructions and/or boulders encountered during installation
- Minimal vibration and disturbance to adjacent structures in close proximity during installation
- Installation possible in difficult or limited access site (tight clearance, interior drilling etc.)
- Installation possible in low headroom sites – pile length can be segmentally increased by installing in shorter bar lengths that are coupled together (low as 6ft clearance)
- Installation possible where elevated groundwater or caving soil conditions are present
- Ideal for foundation underpinning or retrofit applications due to high capacity and ability to be installed in low headroom or restricted space applications
- Equipment allows for tight installation to existing structures/walls to provide supplemental foundation support or upgrade existing foundation elements
Challenges associated with micropiles:
- Development of lateral resistance can be challenging
- Soils and grout spoils created during drilling
The HCM Group has invested in small diameter drilling equipment to be able to provide micropile solutions to challenging projects. At the same time, working with RWH Engineering, the HCM Group continues to develop connections, installation and drilling methods to improve our micropile capabilities.