A Brief History:
The first use of Micropiles dates back to the early 1950’s in Italy, where new methods of underpinning for existing structures were needed to restore structures and monuments damaged during World War II (Lizzi, 1982). Dr. Fernando Lizzi, often referred to as “the godfather of Micropiles”, served as technical director of an Italian specialty contracting firm by the name of Fondedile. It was during that time that Dr. Lizzi developed the “palo radice” or “root pile” now commonly referred to as a Micropile.
What is a Micropile:
A Micropile is a small diameter (305 mm or less) bored/drilled pile that can be installed at various angles to easily accommodate axial and lateral loads. Whether cased or uncased, the Micropiles central reinforcement (Dywidag Bar) provides the necessary conduit for load transfer down to the designed bond zone. The load carrying capability of the Micropile is dependent on the quality of strata, or more specifically, the bond between the grout and the soil/rock. Micropiles can therefore be considered mostly friction piles, however a minimal amount end bearing can be considered in certain instances.
Micropiles are most often installed using two different methods: down-the-hole hammer (DTH) and rotary-percussion (top hammer). Each method of installation has its benefits over the other, but it is soil conditions and application that typically dictate the methodology employed. Micropiles can be installed in soil, rock, through man-made obstructions and in high water table areas to depths of over 200 ft.
Click here to review the Theory of Grout to Ground Micropile Design
Why Use Micropiles:
- Can be installed with little or no vibration (no damage to adjacent structures)
- Micropiles can be installed in 8’-0” of headroom
- Resist tension, compression and lateral loads
- Low displacement at load
- Ability to work with small drill rigs without casing in narrow spaces
- Installed in areas with sloped rock where other traditional deep foundation methods do not perform well
- Low installation noise compared to traditional deep foundations
- Similar installation methods for all ground conditions
- Simultaneous Drill and Grout Installation
- Rotary Percussive Drilling: Allows quick rates of installation
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