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Papers by William Joughin

A method for risk-based design is described in this paper. Probabilistic methods of analysis are ... more A method for risk-based design is described in this paper. Probabilistic methods of analysis are applied to stress modelling to determine the probability of exceeding a given depth of failure. Suggestions are provided for dealing with geotechnical uncertainty. The understanding of aleatory variability can be improved by collecting more data and improving the quality of data through training and quality control. Stress and model uncertainty remains a challenge in geotechnical engineering. Some degree of subjective engineering judgment will therefore always be required in geotechnical design. Acceptance criteria then need to be defined in terms of safety and economic risk. Corporate risk matrices can be used for assessing the risk in terms of the probability and consequence. International safety benchmarking and safety milestones should be considered. The cost of rehabilitation of tunnels and the financial losses due to lost production are assessed using the model. A typical risk matr...

Mining often takes place in areas with steep and variable surface topography. Variable surface to... more Mining often takes place in areas with steep and variable surface topography. Variable surface topography could be due to natural features such as valleys and hills, or man-made features such as excavations caused by surface mining operations or surcharging by dumping of spoil material, or tailings from the metallurgical plant. The research carried out for this project shows that the stability of underground excavations could be adversely affected by the proximity of such topographical features, especially in near surface mining operations of less than 100 m below surface. Perhaps the biggest hazard concerning the influence of surface topography on the loading of pillar workings in near surface and shallow mines is incorrect pillar design. This includes the identification of critical areas under influence of topographical features, and consideration of failure mechanisms not necessarily taken into account under normal conditions. This study shows that standard pillar design techniqu...

South Deep Gold Mine is carrying out massive mining at between 2400 and 2650 m and it is planned ... more South Deep Gold Mine is carrying out massive mining at between 2400 and 2650 m and it is planned to extend this to depths of between 2900 and 3400 m. To facilitate resource estimation, a barrier pillar design was performed. Numerical analyses of the barrier pillars were performed to facilitate the understanding of the mechanisms likely to govern the behaviour of the pillars. The rock mass constitutive behaviour was modelled with the Cohesion Softening Friction Hardening model. Parameters for the analyses were obtained from laboratory tests on intact samples which were adjusted for the rock mass. The derivation of the parameters and the modelled pillar response are discussed in the paper

The nature of this project requires that various types of shotcrete be applied to a tunnel and th... more The nature of this project requires that various types of shotcrete be applied to a tunnel and that the performance thereof under extensive deformation be monitored over a period of time. In order to achieve this, one of the most critical tasks was to obtain an appropriate experimental field site. Finding the best site was of utmost importance to limit the duration of the project. A site needs to be subjected to high mining induced stress increases and associated convergences shortly after application of the shotcrete so that the observations of performance could be completed in the two year time frame proposed.

Journal- South African Institute of Mining and Metallurgy

The first day comprised a workshop on 'Risk in Rock Engineering Design'. Leaders in this developi... more The first day comprised a workshop on 'Risk in Rock Engineering Design'. Leaders in this developing field were invited to present on the application of risk in the design of surface and underground mines and on methods of risk analysis. The workshop concluded with a lively debate, which highlighted the requirement for improved analytical methods for complex mechanisms of failure and to define an acceptable level of risk for design purposes. Technical papers were presented from day two to day four. These included a number of interesting contributions on rock fracture and the mechanics of rock failure. Several papers explored the rock mechanics aspects of mining at great depths and the management of seismicity in mines. New methods of geotechnical investigation were presented and existing methods were critically reviewed. Useful case studies on the rock mechanics aspects of bord and pillar and massive mining methods were discussed. For surface mines, new developments in slope design and slope monitoring were presented. The nine papers selected for this journal are high-quality contributional that provide a sample of the range of topics presented. The symposium was jointly organized by the Southern African Institute of Mining and Metallurgy (SAIMM) and the South African National Institute of Rock Engineering (SANIRE).

At South Deep, mining currently takes place at a depth of between 2400 m and 2650 m below surface... more At South Deep, mining currently takes place at a depth of between 2400 m and 2650 m below surface, but is planned to be extended to a depth of around 3400 m in the future. The orebody comprises Witwatersrand conglomerates and varies from 1 m thick to over 100 m thick and extends over several kilometres. The narrow tabular portion of the orebody (Ventersdorp Contact Reef) is mined using a conventional overhand mini- longwall mining method. The same mining method is currently used to mine a tabular cut within the massive portion of the orebody in order to de-stress the remainder of the massive orebody situated above and below this de-stress cut. A system of regional stabilising pillars, together with the placement of cemented cycloned classified tailings is utilized to minimise seismic energy emission. Mechanised mining methods subsequently are used to extract the remainder of the massive orebody, which has been effectively de-stressed. The regional pillars must be designed to combat ...

In this paper, a risk based approach, has been applied to the design of chromitite pillars. The e... more In this paper, a risk based approach, has been applied to the design of chromitite pillars. The extent of failure in the pillars was modelled using the two-dimensional non-linear finite element program PHASE2. With this program, several different material types were modelled. Strength properties of the materials used in the models were described using Hoek-Brown properties. The variability of the strength properties, pillar dimensions and spans were taken into account by applying the well known Point Estimate Method (PEM). In applying the PEM, many numerical analyses were carried out with varying input parameters. Statistical distributions of pillar safety factors were obtained from the results of the numerical analyses. Probabilities of failure were determined from the distributions. A historical collapse of a large area and current mining, in which only few pillars have failed, were back analysed using this method. The results correspond well with the relative numbers of actual pi...

Journal- South African Institute of Mining and Metallurgy