Hollow Rods

Hollow rods (also called self-drilling anchor rods) are used in ground anchoring, soil nailing, and rock bolting applications. The hollow core allows drilling fluid or grout to pass through the rod during installation, enabling simultaneous drilling and grouting in a single operation.

A drill bit is attached to the threaded end of the rod, and the rod is rotated and percussed into the ground. Grout is pumped through the hollow center and out through the bit, stabilizing the borehole as drilling progresses, eliminating the need for casing in loose or unstable soil.

Common specifications range from smaller diameters like HR25 (25 mm OD) up to larger sizes such as HR38 (38 mm OD), with corresponding inner diameters and thread types (R25 through R38) to match different load and ground conditions.

R-thread rods are typically used for smaller diameter, lighter-duty applications, while T-thread rods are designed for larger diameter rods used in heavier-duty anchoring and pile applications requiring higher load capacity.

Hollow rods are typically manufactured from high-strength steel, chosen for its tensile strength, durability under torsional and axial loads, and resistance to deformation during drilling.

Tensile strength varies by specification, but most hollow rods are rated as “high tensile” to withstand the combined drilling, grouting, and load-bearing stresses encountered in ground anchoring and soil nailing.

Yes, this is one of their primary advantages. The simultaneous drill-and-grout process stabilizes the borehole walls in real time, making hollow rods ideal for loose, sandy, or collapsing ground where conventional drilling would require casing.

A hollow rod has a central channel for grout or flushing fluid and combines drilling and anchoring into one process, while a solid anchor bar requires a separate pre-drilled hole before installation.

Hollow rods are commonly used in slope stabilization, soil nailing, micro-piling, foundation underpinning, retaining wall anchoring, and tunnel support systems.

Rod size selection depends on the required load capacity, soil conditions, and project design specifications. Larger diameter rods (such as HR32 or HR38) generally provide higher load-bearing capacity for heavier structural applications.

The pilot bit OD refers to the outer diameter of the drill bit attached to the rod. It must be matched correctly to the rod’s thread type (such as R32, T38, or T45) to ensure proper drilling performance and grout flow.

No, hollow rods are typically a permanent, sacrificial component of the anchoring system. They remain embedded in the ground or structure as part of the finished anchor, bolt, or pile.

The inner diameter determines the flow rate of grout or drilling fluid through the rod. A larger inner diameter allows for faster grout delivery, which can be important in larger-scale or time-sensitive projects.

Yes, most hollow rod systems are designed with threaded couplers that allow individual rod sections to be joined together, enabling installation to greater depths as required by the project.

Quality hollow rods should comply with relevant geotechnical and construction industry standards for material strength, dimensional tolerance, and load testing, which buyers should verify with the manufacturer or supplier.