Reinforcement Techniques for Weak Rock

The objectives of this project were to define the application of alternate reinforcement and support strategies for the stabilisation of weak strata.

They were achieved by:

• the determination and field validation of reinforcement or alternate support strategies suitable for the stabilisation of weak rock.
  
• The characterisation of the key strength criteria of weak rock, allows prediction of rock types and geological conditions that have poor reinforcement potential and require modified or alternate support strategies.
  

The project has defined a range of failure modes within the strata at all 3 sites investigated. In some cases either the low strength of the strata or the weak bedding planes within the strata have significantly influenced the failure modes.

The computer simulation of the strata at the 3 sites has been shown to be consistent with the failure modes defined by extensive monitoring programs.

The findings indicate that currently available support systems can provide appropriate reinforcement and support to the roadway, although the design of the pattern may be significantly different to those traditionally used.

In the Mid Goonyella seam the possibility exists to use low density (less than 1 bolt per square metre) roof bolting patterns within specific limitations of coal roof thickness and management of structured areas.

In the Lithgow seam (with thick coal roof) the interaction between rib and roof stability has been identified as a major factor in controlling one of the failure modes identified. Providing that adequate rib and haunch support is used, there is a significant potential for controlling this failure mode.

Within the German Creek seam the field monitoring and simulation analysis has identified the principal style of failure modes of the roof and floor with associated information relating to the role played by pore pressure within the strata.

The final report covers a number of areas:

• Development of an improved approach to weak rock sampling and testing.
• Overview of the effect of moisture content on the strength of materials and its variation in different rock types.
• The identification of the influence of pore pressure changes resulting from stress redistribution’s and its effect on stability of openings.
• Assessment of the variability of moisture content with depth and its affect on strata strength.
• Development of improved simulation techniques, which can identify a wider range of potential failure types.
• Development of a rational approach to assess different reinforcement and support methods in the weak rock environment.
• Assessment of different reinforcement methods and design approaches for weak rock environments.