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Micropiles 101

In Middle Tennessee and Southern Kentucky, rock is at a high elevation underground and may be used to the benefit of the construction project.  A popular solution to support heavy loading in the region is the use of micropiles. Read on for an introduction to micropiles.

What is a micropile?

A micropile is a small-diameter pile that is typically made of a steel casing, grout, and steel reinforcement. They are used to provide structural support for new structures, for shoring existing structures, or in some instances to stabilize slopes and excavations.

Micropiles are installed by drilling a hole through the existing soil and into the bedrock below. Once the drill is removed, a steel bar is placed inside the hole and reinforced with grout. When the grout achieves strength, the micropile uses the capacity of the competent rock to support the building’s foundation.

How do I know if I need micropiles?

In the early stages of a project, a geotechnical engineer will evaluate the soil below the surface. In this initial exploration the engineer will determine if a deep foundation system is required based off maximum loads, potential settlement, and topography.

Who needs to be involved?

Typically, there are three parties involved when a facility requires micropiles: a geotechnical engineer, structural engineer, and specialty contractor.

The geotechnical engineer will evaluate the soil and submit their recommendations to be reviewed by a structural engineer. The structural engineer will determine the best solution for the project and provide locations and loading criteria to a contractor. Then a specialty contractor is brought in to design and install the micropiles based on the geotechnical report and the structural engineer’s capacity needs.

What are the benefits of micropiles?

A micropile is a practical and cost-effective solution for significant axial loads and moderate lateral loads.  The equipment used for drilling and grouting is relatively small and may be used in restrictive areas that conventional pile installation equipment cannot.  It also causes minimal vibrations and noise, reducing the interruptions for a facility upgrade.  Cost overages due to variations in existing rock are typically smaller compared to other deep foundation systems.