High-capacity, small-diameter, drilled deep foundation elements that are used to support new foundations or to underpin existing foundations.
Piling Systems Drilled Micropiles
Drilled Micropiles (DMPs or mini-piles) are high capacity, small diameter, drilled deep foundation elements that are used to support new foundations or to underpin existing foundations. Drilled Micropiles commonly consist of combinations of steel casing, threaded bar, and grout. Micropiles obtain their geotechnical capacity through side friction (also referred to as bond stress) between the grout and the surrounding soil or rock, and, in some cases, also end bearing. Drilled Micropile construction methods vary, depending on project-specific conditions, but are typically installed by advancing a grout-encased steel central bar with or without steel casing to a predetermined design depth using rotary-wash or compressed air drilling methods. A simple method of building a micropile involves predrilling a hole (with a casing if the hole is collapsible) and filling the cavity with grout, typically through tremie methods, then lowering a solid steel-round textured bar with centralizers into the bore. In some cases, the casing is gradually withdrawn, creating a bond zone between the grout and surrounding soil or bedrock. Casing can remain in the ground permanently to facilitate structural connections, for seismic design considerations, or for other design considerations.
Self-advancing micropile drill methods are also used, involving a hollow central bar, a sacrificial bit with ports, and an external full depth or partial depth casing as needed to control overburdened soils. In this case grout is pressurized down through the hollow bar, out the grout ports, and a pressure head is maintained so that the annulus in the soil around the bar is pressurized with grout. When full or partial depth casing is used, the frictional capacity must be adjusted. The casing in the upper sections of a micropile can also serve to increase lateral resistance and bending resistance for the micropile, and can assist with more versatile connections to structural components at or above grade.
Drilled Micropiles are particularly useful in limited-access situations adjacent to vibration-sensitive structures, and when penetration through relatively dense and/or obstruction-laden fill is required. In fact, drilled micropiles are one of the most effective techniques for penetrating obstructions.
- Working with Obstructed Soils
- Supporting Concentrated High-Weight Loads
- Sites That Require Low Noise/Vibration
- Working in Restricted Spaces
GeoSolv’s Piling Systems offer distinct advantages for various construction challenges compared to traditional methods such as driven piles (H Piles, Pipe Piles, Precast Concrete Piles), caissons (pier foundations, bored piles, drilled shaft piles), or continuous flight auger piles (CFAs, auger cast piles). To learn if one of GeoSolv’s Innovative Foundation Solutions is right for your project, contact us today for an obligation-free feasibility report or proposal. We are always happy to help you avoid the risks associated with poor soils and deep foundation systems.
Hollow Bar Micropiles are drilled into the ground using a sacrificial drill/grout tip while pressurized grout is pumped down the hollow bar while drilling. Micropiles can be used for practically any soil condition, and load is gained through bond stress between the grout and the surrounding soils.
Micropiles have the advantage of being the one piling system that has the best chance of penetrating obstructions during installation. A wide variety of drilling tips are available for different soil conditions.