Hollow bars are fully threaded bars with hollow centers to allow the flow of grout, manufactured in 10 foot sections, capable of drilling holes utilizing sacrificial bits that will advance the tendon to the required depth while simultaneously grouting. This simplified process creates the steel reinforcing portion of an anchor or pile. Hollow bar products are a valuable and multi-functional addition to the geotechnical contractor’s toolbox. They can be used as tie back or tie down anchors, rock anchors, soil nails and micropiles in a large array of challenging applications.
There are three basic types of drill bits for use with hollow bars. Versatile cross cut bits in carbide or hardened steel capable of drilling in various subsurface conditions, carbide button bits for drilling in rock and extremely dense formations, and steel stepped clay bits for cohesive soils. The selection of the drill bit type and size is based on the material that is being drilled through, the diameter of the hollow bar, and the desired borehole diameter. A larger borehole diameter provides greater load carrying capacity and greater grout cover. Grout cover protects the anchor rod from corroding. Depending on the actual soil type, a 3 inch diameter bit can produce a 6 to 8 inch diameter grout column.
Production rates are increased through the use of hollow bar systems, as compared to traditional solid bar anchors. This is especially true when drilling through “difficult conditions”. In sites with low headroom, large scale drilling rigs and hole casing systems can be avoided. With drill rigs where “through the head grouting” is not available, side-inlet grout swivels can be used to retrofit standard rotary percussion drills.
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Hollow Bar Corrosion Protection
The level of corrosion protection is dependent on the anticipated service life of the anchor, installation methods, and the corrosion potential (aggressiveness) of the environment. The Federal Highway Administration (FHWA) has studied the effects of installation on both galvanized and epoxy coated bars as reported in FHWA CFL/TD10-002. This study revealed epoxy coatings were both partially and completely removed at the leading edge of the thread profile and around the couplings.
The installations were constructed using hollow bars as both the drill rod and reinforcement. The effects of the coating removal reduced the service life of the bar substantially by creating concentrated locations for potential corrosion. As such, the designer should evaluate all possibilities when determining the level of corrosion protection required.
Hot Dipped Galvanizing
Hot dipped galvanizing is a form of galvanization and is the process of coating a base metal such as steel with molten zinc. The zinc acts as a sacrificial material to the steel. The galvanized coating is manufactured in accordance with ASTM A 53 standards and is more resistant to handling than epoxy coatings. Thermal diffusion galvanization is also available.
Sacrificial Steel
Using sacrificial steel as a form of corrosion protection requires a geotechnical evaluation of the corrosivity of the soils. The estimated loss of steel thickness is calculated and then the hollow bar is designed with the additional increase in thickness.
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Hollow Bar Systems: Simplifying Complex Foundation Work
At Nucor Skyline, we've optimized hollow bars that deliver exceptional performance in foundation projects. Our hollow bar technology provides a streamlined drilling and grouting process, eliminating separate drilling operations and maximizing efficiency in challenging ground conditions where traditional methods fall short.
Our domestic hollow bars provide numerous advantages that make them the preferred choice for demanding geotechnical applications:
- Single-pass drilling and grouting for accelerated project timelines.
- Minimal equipment required on-site.
- No need for drill tooling or casing.
- Superior performance in unstable soil, fractured rock, and limited-access sites.
- Manufactured in multiple diameters and custom lengths to meet specific project requirements.
Hollow Bars for Geotechnical Reinforcement
Nucor Skyline's hollow bars deliver superior geotechnical reinforcement for critical infrastructure projects, providing exceptional stability for retaining structures, slope protection, tunnel construction, and deep foundation applications. Our domestically manufactured high-strength steel hollow bars effectively anchor into challenging soil conditions, delivering the long-term support your projects demand.
Our hollow bar systems have been successfully implemented across diverse geotechnical applications that require maximum reliability and performance:
- Micropile foundation systems for reliable structural support.
- Rock stabilization in underground construction.
- Engineered soil nail systems for slope reinforcement and erosion mitigation.
- High-capacity tiebacks and retaining wall anchorage.
Engineered Solutions for Challenging Ground Environments
When your project faces unpredictable ground conditions, Nucor Skyline's hollow bars provide the structural reinforcement needed for soil strength and stability. The innovative hollow core bars enable simultaneous drilling and grout delivery, creating maximum bond strength even in problematic soils, clay formations, and fractured rock environments. Nucor Skyline can also assist in preliminary anchor and micropile design, giving you an edge in your project procurement and bidding.
Nucor Skyline hollow bars improve ground stability through multiple mechanisms that work together to create soil reinforcement:
- Reinforces compromised slopes and embankments with precision-engineered support.
- Minimizes soil displacement and erosion potential for long-term site stability.
- Provides enhanced structural resilience in seismically active regions.
- Delivers lasting stability for critical infrastructure investments.
High-Capacity Foundation Support with Hollow Bar Technology
For superior foundation performance, Nucor Skyline's hollow bars offer distinct advantages over conventional piling methods. Their exceptional load-bearing characteristics and installation versatility make them the ideal solution for projects with restricted access, poor soil conditions, or complex site challenges.
Our hollow bar systems are specifically engineered to meet the demands of today's most challenging foundation applications:
- Engineered for high-capacity micropile applications requiring maximum structural integrity.
- Ideal for underpinning existing structures during renovation and retrofit projects.
- Optimized for effective load distribution in transportation and infrastructure construction.
- Trusted for both temporary construction support and permanent excavation stabilization.
Advanced Soil Stabilization Applications with Hollow Bars
Effective soil stabilization is critical to the performance and durability of infrastructure projects, transportation networks, and construction developments. Nucor Skyline's hollow bars are specifically designed to enhance soil strength, optimize load distribution, and prevent ground settlement.
Contractors and engineers trust Nucor Skyline hollow bars for their effectiveness in a wide range of soil stabilization applications:
- Advanced soil nail systems for comprehensive landslide prevention.
- High-pressure grouting capabilities delivered through our hollow bar systems for enhanced soil density.
- Engineered deep foundation anchoring for structure stabilization in challenging soil conditions.
- Tunnel and excavation support for worker safety and structural integrity.
Frequently Asked Questions
What advantages do Nucor Skyline's hollow bars offer for challenging ground conditions?
Our hollow bars excel in unstable soil conditions where conventional drilling methods struggle. The self-drilling design eliminates the need for temporary casings, reducing installation time and costs while providing superior anchoring in loose soils, fractured rock, and water-bearing strata. This makes them particularly valuable for urban construction, rehabilitation projects, and sites with limited access.
How do I select the right hollow bar diameter for my project?
Choosing the appropriate hollow bar depends on your project's load requirements, soil conditions, and installation constraints. Nucor Skyline's engineering team provides technical consultation to help determine the optimal bar diameter, length, and accessories based on your specific geotechnical parameters. Our bars range from smaller diameters for soil nailing to larger sections for high-capacity micropiles.
Can Nucor Skyline provide both hollow bars and threaded bars for the same project?
Yes, many of our customers utilize both product lines within the same project to address varying site conditions and structural requirements. For example, threaded bars might be specified for main anchors in stable soil areas, while hollow bars could be used for challenging sections with collapsing soils or where water infiltration poses drilling difficulties. Nucor Skyline's product range allows for optimized, site-specific solutions.