Self-Drilling vs. Pre-Drilled Hollow-Core Rock Bolts: What Tunnel Contractors Should Confirm Before Ordering

Two quotations can describe threaded hollow rods, but still cover different installation tasks. One suggestion may be a self drilling system. Another possibility is to insert hollow bolts after drilling separate support holes.

For tunnel contractors, this difference will affect the component list, equipment interfaces, and questions that need to be answered before purchase. The investigation of 'hollow anchor rods' alone leaves too much room for explanation.

The use of pre drilled hollow anchor rods in this article refers to hollow anchor rods used to insert support holes into individual boreholes. Consider it as a description of installation arrangements and require each supplier to identify the actual products and methods behind their terminology.

Confirm whether the drill pipe is part of the drilling operation

In the self drilling device, the hollow rod forms a part of the drill string, moves forward with the drill bit, and remains as steel bars. In the pre drilling arrangement discussed here, separate drilling equipment forms holes before inserting hollow bolts.

Even if manufacturers use the relevant rod series in both arrangements, this distinction is still important. A rod with similar appearance is not sufficient to prove that the proposed product is suitable for the same drilling and installation tasks.

Before discussing the price, provide the supplier with the specified installation method and request confirmation based on the proposed product drawings. If the project documents are unclear, please submit the issue to the project's technical team instead of letting the quotation determine the method.

Before comparing products, compare installation tasks first

Use the table below to organize supplier discussions. This is a procurement comparison, not a design selection rule.

The above installation differences follow the product descriptions of Epiroc's self drilling and hollow series; The remaining lines are purchase checks used to address proposed configuration issues.

Suppliers may use terms such as self drilling anchors, hollow rods, injection bolts, or hollow bolts in different product ranges. Check the installation instructions and component list, rather than treating these names as interchangeable.

Match product data with project requirements

When contacting suppliers of self drilling anchor rods or hollow anchor rods, please confirm the specified drawing version and product characteristics.

Request confirmation:

• Reinforcement length, external dimensions, and internal holes.
• Thread name and drawing used to define the thread.
• The attributes and testing information of the precise proposed model that has been published.
• The required surface treatment or anti-corrosion arrangement.
• Connect details and specified header components.
• Any discrepancies between the proposed product and project schedule.

Separate the required values from the values provided by the supplier. A response that only lists product series or nominal sizes cannot clearly determine what will be delivered.

Also ask what each performance document covers. Does it describe the rod, connection, component, or installed element? Record these differences so that the project team can evaluate the evidence according to their requirements.

If an alternative model is provided, please request a separate proposal and clearly list its differences. Do not merge it with the specified project quotation.

Check the drill bit, connectors, and equipment interfaces

For the self drilling anchor system, the drill bit is an important component of the proposed supply package. The manufacturer's catalog provides different types of drill bits for different ground conditions, so it is necessary to check the drill bit configuration according to project requirements.

Request the proposed drill bit identification and drawings, and inquire about how it can be connected to the designated rod. If the bit selection is still unresolved, please determine who will review it and what ground information is needed.

The connection also deserves the same attention. Require suppliers to distinguish between rod type extension couplings and adapters used on drilling equipment. Identify each item on the parts list, including whether it is supplied as part of the order.

The equipment discussion should determine the actual drilling rig and related tools. Request written clarification on the required equipment and injection interfaces. The statement that a system is "suitable for ordinary drilling rigs" does not provide a specific connection.

For pre drilling options, confirm which party provides separate drilling tools and what equipment is required to insert and inject the proposed bolts. Removing a point from the supply list alone does not establish a complete installation package.

Clearly define the grouting or injection arrangement

Self drilling describes the drilling function of the system. The quotation should also specify the proposed injection materials and installation instructions applicable to the provided configuration. The manufacturer's instructions include different flushing and injection arrangements, which should be checked for the selected product.

Send relevant project requirements and request suppliers to confirm:

• The cement slurry or resin system covered by the product information.
• The required injection connections and related accessories.
• Which pumps, hoses, or adapters are included or not included.
• Which instructions describe the recommended installation sequence.
• What records and tests are required for project review and acceptance.

If the quotation mentions one-time drilling and grouting, please inquire about what the statement includes and whether other stages are specified. Do not interpret a brief product description as a complete construction plan.

The mixing ratio, operation settings, installation steps, and acceptance criteria should be addressed through approved project documents and instructions for the selected system. They should not be provided by a universal procurement list.

Confirm a complete and comparable supply scope

Before placing an order, please provide a schedule itemized instead of a single line of "hollow bolts"

Mark each item as included, excluded, or priced separately. Ask who is responsible for resolving any interfaces between projects provided by different parties.

Compare the quotation with the same schedule. The price including only rods and the price including drill bits, couplers, plates, and documents represent different supply ranges. Confirm technical configuration before evaluating business differences.

Close open-ended questions before placing an order

End the discussion with a brief confirmation note:

• Are the required installation arrangements consistently stated in the drawings, quotations, and suggested explanations?
• Have you confirmed the exact model provided and the relevant product data?
• Have drill bits, connections, head components, and equipment interfaces been taken into account?
• Is the injection schedule clear, including any equipment provided separately?
• Have deviations and alternative solutions been listed for project review?
• Have the required documents and responsibilities been agreed upon?

If changing from pre drilling arrangement to self drilling arrangement, or vice versa, please clearly describe the proposed changes. Obtain technical review of the change from the project, rather than treating it as a substitute for similar procurement.

The comparison should answer whether the provided configuration matches the installation task of the project. It should not assume that any system is always stronger, faster, or cheaper.

Prepare a clear inquiry for CQ anchor rods

Send the specified installation method, relevant drawings, reinforcement and connection requirements, component quantity, and delivery destination to CQ Rockbolt. Include a list of documents required for project review.

A concise survey can illustrate:

Please refer to the designated [self drilling/pre drilling hollow] layout shown in the attached document. Determine the proposed drill rod, required drill bit configuration, couplings, head components, and injection fittings. List excluded items, deviations, and available technical records separately.

Before finalizing the order, please confirm with CQ Rockbolt which available products, components, and documents can address the inquiry.