Establishing the in situ rock bolt behaviour underground in order to model and design improved rock bolt support systems

The Challenge

Although rock bolts have formed a fundamental part in stabilising and fortifying underground tunnels since the 1890s, very little is known about how much pressure they can withstand. Current design practice only considers the axial load capacity of the rock bolt yet rock bolts are subjected to combinations of axial, shear and bending in situ.

In spite of these combined effects, only tensile capacity is currently considered in design and testing and this isn’t the weakest performance link. Shear capacity, on the other hand often is, which leads to support designs that tend to overestimate the effectiveness of rock bolts. 

Proposed Solution

This project seeks to understand in-situ rock bolt performance to:

• Develop computer models which provide a more accurate and visual representation of how rock bolts perform underground
• Create instrumented rock bolts that can measure shear and tensile loads along their length with the potential to determine the principal stress directions close to excavations

In the future, the humble rock bolt could serve a greater purpose by showing the directions of the principal stress directions in the immediate rock which can be used to better calibrate computer simulations. This will enable the ability to predict potential failure rather than simply trying to prevent it.

Proposed Benefit to WA

• Improved safety in underground mines from better quantification of safety factors
• Better and more reliable rock bolt support, considering both shear and tension, enables improved designs as mines go deeper
• Accurate representation of rock bolts in predicative computer models improves confidence in mine design
• Ability to check in situ loading in critical locations to enable proactive mining operations
• A reliable method to monitor rock movement (in pillars for example) prevents unexpected mining outcomes
• In-situ sensing leading towards the possibility of determining principal stress directions close to excavations

Keywords: rock bolts; numerical modelling of rock bolts; analytical modelling of shear and tensile load; instrumented rock bolt; fibre optic sensing; combined shear and tension