Micropiles, also called mini piles, are often used for underpinning. They are also used to create foundations for a variety of project types, including highway, bridge and transmission tower projects. They are especially useful at sites with difficult or restricted access, or with environmental sensitivity.
Foundations provide support for structures, transferring their load to layers of soil or rock that have sufficient bearing capacity and suitable settlement characteristics. Very broadly, foundations can be categorized as shallow foundations or deep foundations.
Pile foundations are deep foundations. They are formed by long, slender, columnar elements typically made from steel, reinforced concrete, or sometimes timber. A foundation is described as piled when its depth is more than three times its breadth.
Micropiles are piles that have a relatively small diameter, typically in the range of 4 inches to 10 inches. Installation of micropiles through overburden and into rock can be achieved using various methods including sonic drilling.
Sonic Drilling is ideal for the installation of micropiles in varying geological formations. Sonic Drilling is 3-5 times and sometimes 10 times faster than conventional drilling methods in most lithologies. The vibration induced in the drill string from the sonic head fluidizes the formation in a very small boundary layer around the drill string. This fluidization results in a dramatic reduction in friction, thereby allowing for increased penetration rate.
The Sonic Drilling process creates a fully cased bore in which the reinforcing steel bar can be installed inside the casing and then the casing can be extracted gently using vibration. The grout is also installed using gentle vibration to “knit” the grout into the native soil to create a tight seal.
For micropiles installed on sites with contaminated soil and groundwater, the Sonic Drilling process creates up to 80% less waste to dispose of. Combining this benefit with the increased drill rates discussed above ensures that overall costs for the project will be reduced.
The Terra Sonic International 150 CC Sonic Drill Rig is ideally suited for foundation drilling applications.