ACARP PROJECT C27040: Development of a Numerical Modelling Approach to Better Understand the Effect of Cable Bolt Performance on Roof Failure Mechanisms in Varying Rock Mass Conditions

ACARP PROJECT C27040: Development of a Numerical Modelling Approach to Better Understand the Effect of Cable Bolt Performance on Roof Failure Mechanisms in Varying Rock Mass Conditions

This project provides an improved numerical modelling approach to enhance mine safety, increase productivity and reduce costs via fit-for-purpose designs and more effective applications of cable bolts in different geotechnical environments. The project objective was to better understand the roof failure mechanisms using a newly developed numerical modelling tool. The questions addressed included whether pretension can reduce the full capacity of a cable bolt, in which types of ground conditions pretension should or should not be used, how much pretension is appropriate if required, how the installation angle will affect cable pretensions and the influence that ground and stress conditions can have on the performance of support systems and resultant roof behaviour.

Three universities each undertook a portion of the work within this project:

University of Wollongong conducted a laboratory study to identify significant variation in cable bolt performance in rock of differing strength under standardised testing as well as double shear testing at different angles of orientation (inclination).
University of Southern Queensland simulated the laboratory experiments by a discrete element method software package. Laboratory test results provided the key data for developing laboratory-scale numerical models to predict cable bolt performance in double shear experiments.
University of New South Wales took learnings from the laboratory-scale models and guided the team to select suitable constitute models and input parameters required to develop field-scale numerical models to simulate cable bolt performance in various geological and geotechnical environments. A field-scale numerical model with various cable bolting designs has been developed, which can be adapted to simulate different geological and geotechnical conditions.
The development of an advanced numerical modelling tool also enabled a broad range of factors to be evaluated for their contribution to the roof failure mechanisms in underground roadways. In particular, the model considered the effectiveness of varying ground support configurations to be analysed in a range of rock mass conditions such as rock strength, bedding plane stiffness, and in-situ stress. For a cable bolt element, its loading capacity, pretension, installation angle, grout modulus/capacity, support density and plate strength were analysed in detail to understand their impact on support performance and failure mechanism.

The performance of cable bolts was studied in field-scale models based on the setup of one mine which has challenging geotechnical conditions and has experienced roof instabilities. These models used advanced simulation techniques that were not fully implemented before by previous projects, such as ground relaxation, different boundary conditions, and application of the neutral point in modelling. The research results are expected to provide guidance on the selection of cable bolt pretension and installation angle in various roof strata and in-situ stress conditions, which can ultimately improve ground support performance in the underground coal mining industry.

While the published outcome contains the three separate reports (one from each university) these are summarised in an executive summary report that describes:

Laboratory-scale cable bolt testing;
Numerical modelling of cable bolts in laboratory experiments; and
Numerical modelling of cable bolts and their performance in field conditions. Although this report has three parts and each part had a lead partner to ensure clear responsibility and avoid work overlap, all three universities worked collaboratively on each part through data exchange, knowledge sharing, laboratory facilities and software sharing.

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