As geotechnical engineers, we often spend valuable time on repetitive calculations during rock bolt and anchor design. That's why I've developed a free, web-based Rock Bolt Design Calculator to streamline this process!
The Rock Bolt Design Calculator is a free professional geotechnical analysis tool for designing rock bolts and ground anchors based on Australian Standards (AS4678-2002, AS5100).
Through this blog I am trying to explain, how can we design a rock anchor using rock bolt designs calculator.
Design
You are designing rock bolts for a tunnel support system in moderately weathered sandstone. The design must comply with Australian Standards (AS4678-2002, AS5100).
Given Site Data:
- Rock type: Moderately weathered sandstone
- Available grout: 32 MPa cement grout
- Rock-grout bond stress (from pull-out tests): 500 kPa
- Project category: Category 2 (Normal importance)
- Proposed bolt: N24 deformed bar (Fu = 168 kN)
Objective: Determine the required bond length for the rock bolt.
Step-by-Step Design Using the Calculator
Step 1: Open the Calculator
Navigate to the Australian tab (default view).
Step 2: Enter Concrete/Grout Properties
The calculator will automatically compute:
f'ct = 0.36 × √32 = 2.04 MPa (Ultimate anchorage bond strength)
Step 3: Enter Anchor Properties
Step 4: Enter Drill Hole & Bond Stress Properties
Step 5: Select Reduction Factors
Based on project requirements and AS Standards:
Step 6: View Calculated Results
The calculator automatically displays:
Design Summary
Design Decision:
Minimum required bond length = 4.052 m
Adopt L = 4.5 m (with safety margin)
The Grout-Rock interface governs the design because it requires a longer bond length.
