This standard provides guidelines for the design, construction, and testing of permanent and temporary prestressed rock anchors. It covers material specifications, design considerations against failure modes, construction procedures like drilling and grouting, and detailed testing protocols for anchor acceptance.
Guidelines for the design and construction of prestressed rock anchors
Quick Reference Values
Minimum centre-to-centre spacing of anchors1.2 m or 4 times hole diameter, whichever is greater (Clause 4.2.2)
Minimum fixed anchor length (bond length)3.0 m (Clause 4.3.2)
Maximum test load in performance/proving testShould not exceed 80% of the characteristic strength of the tendon (Clause 7.3.1)
Maximum lock-off load (transfer load)1.1 times the design load, but generally kept around 70-75% of tendon's characteristic strength (Clause 7.4.2)
Minimum 7-day cube strength of grout17 MPa (Clause 5.3.3)
Key Formulas
Pa = π * d * L * τ_s — Allowable load based on rock-grout bond stress (where d is hole dia, L is bond length, τ_s is bond stress)
Practical Notes
Corrosion protection is critical for the long-term performance of permanent anchors; double corrosion protection systems are often recommended in aggressive environments as per Clause 4.5.
On-site testing (proving tests, performance tests) is mandatory to validate design assumptions, especially the grout-rock bond strength, which is highly variable and site-specific.
Careful control of drilling alignment and thorough flushing of the drill hole before grouting is essential to achieve the required bond length and capacity.