Proceedings of the 2004 Coal Operators\u27 Conference

Proceedings of the 2004 Coal Operators\u27 Conference. All papers in these proceedings are peer reviewed in accordance with The AUSIMM publication standard

Proceedings of the 2009 Coal Operators\u27 Conference

Proceedings of the 2009 Coal Operators\u27 Conference. All papers in these proceedings are peer reviewed. ISBN: 978 1 920806 95 8

Numerical Simulation of Fully Grouted Rock Bolts

This chapter describes the application of numerical modelling to civil and mining projects, particularly rock bolting, developing a Final Element (FE) model for the bolt, grout, rock, and two interfaces under axial and lateral loading, verifying the model, analysing the stress and strains developed in the bolt and surrounding materials. Numerical methods are the most versatile computational methods for various engineering disciplines because a structure is discritised into small elements and the constitutive equations that describe the individual elements and their interactions are constructed. Finally, these numerous equations are solved together simultaneously using computers. The results from this procedure include the stress distribution and displacement pattern within a structure. Numerical modelling includes analytical techniques such as finite elements, boundary elements, distinct elements, and other numerical approaches that depend upon the material. The finite element method FEM is considered to evaluate the behaviour of materials and their interactions in a fully grouted bolt which is installed in a jointed rock mass. The simulations were carried out by ANSYS code

Proceedings of the 2017 Coal Operators\u27 Conference

Proceedings of the 2017 Coal Operators\u27 Conference. All papers in these proceedings are peer reviewed. ISBN: 978174128261

Improvement of Rock Bolt Profiles using Analytical and Numerical Methods

The anchorage capacity of fully grouted bolts has been studied for many years, however the bolt rib profile and its effect on bolt shear resistance is poorly understood. A new development in calculating load transfer capacity between two rib profiles of varying geometries is discussed. The derived mathematical equations presented calculate the stress distribution adjacent to the fully grouted bolt and bolt pull out force needed to fail the resin. The Fast Lagrangian Analysis Continua (FLAC) program was used to verify the calculations of stress within the resin. The novel idea of coupling the bolt geometry with the calculated stress provides another powerful tool to investigate the bolt profile configuration and its effects on the load transfer mechanism for the benefit of the mining industry

A critical evaluation of dust sampling methodologies in Longwall Mining in Australia and the USA

Questions relating to the validity and subsequent suitability of the current dust sampling methodologies utilised in Australia and the USA have recently come under scrutiny. The reason for this scrutiny is that there has been a significant increase in Coal Workers‟ Pneumoconiosis in the USA over the last few years despite recorded conformance to exposure level legislation. The opinion by many in the underground coal mining operators in Australia is that the current testing regime tells them very little about the actual operational production of dust on the longwall face in relation to where it is produced, how much is produced or how efficient installed controls are at preventing this dust from entering the atmosphere. Evaluation of the current testing regimes in Australia and the USA are proposed, which identify limitations that are raising questions relating to its suitability to ensure worker health in the underground coal mining operator

Shear strength properties of clean and clay infilled rock joints: an analysis of the impast of moisture content under CNL conditions

Rock joints are a type of fracture or discontinuity that have little or no movement that is parallel to the plane of fracture caused by forces acting perpendicular to the fractured walls, where the opening of the break is parallel to the face of least resistance. These are common phenomena in geology around the world and range from small scale to tectonic fault lines. The first part of this project focused on the effect of clean rock joints on the shear strength of the joint at normal loads of 100, 300, 500 and 700 kPa. Rock joints leave an opportunity for infill to occur in the form of soil, water, or mineral precipitates. The second part of this project focuses on the effects of sodium bentonite clay infill with moisture contents of 0%, 10% and 16% and normal stresses of 100, 300, 500 and 700 kPa on the shear strength properties of rock joints. As shear strength is a controlling factor for slope stability, it is important to continue research into this area in order to optimise future engineering project outcomes. There are two main loading conditions for the direct shear testing of rock joints; Constant Normal Loading (CNL) and Constant Normal Stiffness (CNS). As CNL and CNS conditions are representative of different real-world applications it is critical to understand the scope and context of each investigation. This project was conducted under the CNL boundary condition as it predominately focuses on the impact of moisture content on the shear strength of rock joints under unsaturated conditions. These conditions are more likely to occur in shallow rock formations due to the infill and moisture fluctuations that are caused by water infiltration and precipitation

Why the peak shear load of indented cables increases with increased wire failures?

In shear testing of indented cables it has been found that indented cables peak share load failures behave contrary to the normal failure behaviour. The gradual strength loss with each individual wire failure in an indented cable strand may not lead to subsequent peak shear failure of the remaining strands in decline. This failure behaviour is characteristic of indented cables and occurs irrespective of the test method used (single shear or double shear test). Accordingly in this study all wires in a tested cable strand were instrumented with strain gauges. Each instrumented wire was individually colour coded to assist in determining the location of the wires in the strand circumference with respect to the direction of shear. The location of wires in the perimeter was identified at the sheared joint surface areas. During testing of the cable using a circular MKIV double shear apparatus (Naj Aziz DS Box) the initialisation of wire failure was identified by the strain gauge readings. This data found that the wires failing early were located on the upper segment of the bent strand during shearing process, indicating that the indentations introduced stress concentration spots on the wire, causing the strand wires to fail prematurely with less tolerance to bending than smooth wired cable

Development of a wireless system to measure the strain/deformation of rock bolts

In this study a smart set-up integrated with rock bolts was proposed to automatically monitor, record and analyse rock mass deformation. The proposed system which includes sensors and a wireless data acquisition system, rapidly and readily generates data sets along with customisable graphs, calculations and analysis in a cloud system and can be used in modern mining. To evaluate the developed technique, rock bolts were instrumented lengthwise using resistive strain gauges and then connected to the wireless data logger system. Elastic tensile tests as well as pull-out tests were conducted and the strain values along the rock bolts were successfully and accurately measured, recorded and uploaded to the cloud system

Strength properties of grout for strata reinforcement

An experimental study was carried out on grout samples prepared from both Stratabinder and BU100 cementitious products. Samples were prepared with various water to grout ratios and tested for uniaxial compressive and shear strength. Triaxial tests were performed on cylindrical samples to determine values for internal friction angle, cohesion and tensile strength. It was found that the water to cement ratio affects the uniaxial compressive and shear strength of grout. The triaxial test indicated that both internal friction angle and cohesion of Stratabinder do not differ significantly from BU100