Hollow Bar Micropiles

Hollow bar micropiles are a type of micropile with a hollow core and a disposable drill bit on the end designed to consolidate the number of installation steps when compared to other micropiling methods. The drill bit is selected to core through the specific soil type at the site (e.g., clay, sand, gravel, rock) at the required pile diameter.

As the drill digs to the specified depth, a threaded hollow bar follows, acting as a conduit for cement grout to pass through as it’s ejected from the end of the drill bit. Once the drill reaches the required depth, micropile drilling, flushing, grouting, and installation have already been completed, significantly reducing the number of steps required to achieve a reliable anchor point.

Because drilling, grouting, and installation happen simultaneously, hollow bar micropiling requires no pre-drilling or pre-/post-grouting, not only reducing the number of steps but also the amount of equipment needed for installation. A rock drill and grout plant are generally all that’s required for hollow bar micropiling. Even with less equipment, however, it’s still possible to maximize micropile strength by increasing grout pressure to enlarge pile diameter. For example, a drill bit with a 2.5-inch diameter can produce a group column of up to eight inches.

The Role of the Hollow Bar

After acting as both the drill rod and a conduit for grout, the hollow bar then remains in place as a steel reinforcement bar following installation. The type of steel or protective casing used for the hollow bar is optimized for site soil conditions to prevent corrosion over time and ensure a long-lasting anchor pile. Hollow bars also offer superior increased bending capacity, readily absorbing lateral, compression, and tension forces as soil shifts.

When you’re considering micropiling for your next ground improvement project, you have two choices: hollow bars and solid bars. The key difference comes down to the number of installation steps and how much equipment you need.

Solid Bar Micropiling

Solid bar micropiling is a conventional approach to anchoring deep pile foundation systems. However, they are limited in application and require additional steps before and after installation. Solid bar micropiles can only be installed in areas with shallow rock foundations, and specialized casings are required for softer soils.

Installation is more involved because pre-drilling, pre-grouting, and post-grouting are required, increasing project time, cost, and the amount of equipment needed. Prior to solid bar installation, a hole first has to be drilled and grouted. Grouting is again required after the bar is installed. As a result, solid bar micropiling is better suited to new construction foundation improvement but often isn’t feasible for existing buildings.

Hollow Bar Micropiling

Hollow bar micropiling developed after solid bar micropiling, improving the conventional process by eliminating the need for pre-drilling since drilling occurs concurrently with hollow bar installation. Grouting is also part of the installation process, so the need for pre- and post-grouting are eliminated. Hollow bar micropiles are also more versatile than solid bar micropiles. They can be optimized to provide a reliable pile for virtually any soil type with a wider range of pile diameter and depth options.

Along with soil conditions, one of the most important considerations when deciding between solid bar and hollow bar micropiling is the amount of working space at the site. Since solid bar micropiles require more installation equipment, it can be difficult or impossible to anchor them in areas with limited space. Hollow bar micropile installation, on the other hand, involves less equipment, and it’s much easier to coordinate in tight work areas, even with limited overhead and lateral movement. Because of this, hollow bar micropiling is suitable for both new construction foundation improvement and ground improvement for existing structures.

For more than 20 years, Intech Anchoring has supplied commercial, residential, and industrial contractors with advanced ground improvement solutions, including products and services, such as hollow bar micropiling. If you need to understand which deep pile foundation options are right for your next ground improvement project, the experts at Intech Anchoring can help you get started. Whether you need help with new construction foundation improvements or ground improvement for existing structures, we arrive ready with the capabilities and experience to oversee every step from a preliminary project meeting to project completion.