micropiling

Micropiling is a geotechnical construction technique used to install small-diameter reinforced concrete piles that transfer loads from structures to deeper or more competent soils or rock. The method is chosen for use in restricted spaces, near existing buildings, or in poor ground conditions where conventional piles are impractical.

Diameters typically range from about 100 to 300 millimeters (4 to 12 inches), with some designs up to about 600 millimeters. Piles are formed by drilling or driving a borehole, installing a steel reinforcement cage, and grouting the hole to create a composite pile. Temporary casing or drilling fluids may be used to stabilize the borehole during installation, and high-strength cementitious grout is common.

Loads are carried by a combination of end bearing and skin friction along the grout-soil interface and reinforcement. Micropiles may be used singly or in groups to form foundations, underpin existing structures, strengthen slopes, or anchor retaining walls.

Advantages include small diameter, relatively low vibration and noise, the ability to install in confined spaces or through obstructions, and suitability for sites with poor or varying soils. They can be installed with limited access and without substantial ground displacement, making them useful for retrofitting or remediation projects.

Limitations include upper bound on individual pile capacity, requiring group action for large loads, and reliance on the quality of grout and the bond to reinforcement. Design must account for soil conditions, groundwater, and load paths to the existing foundation.