Underground potash mine design based on rock mechanics principles and measurements

PhD ThesisThe design criteria for an underground potash mine are established on the basis of rock mechanics principles and measurements taken at the Cleveland Potash Limited Boulby mine in North Yorkshire, thgland. The requirements of the mine design are that a maximum and efficient extraction ratio is achieved, stable and safe working conditions exist within the mines and no damaging subsidence occurs on the surface. In particular, the workings at Boulby are at a depth of 1100 metres below the surface and are overlain by water bearing Bunter sandstone strata, 120 metres above the potash horizon. Consequently, the major problem of the mine design concerns minimizing the subsidence-induced strains at the base of the Bunter sandstone in order to prevent a possible water inrush into the mine. The various design parameters to meet these requirements are established on the basis of theoretical, laboratory and tin-situs analyses. A study of Canadian potash mining practice is included to provide valuable design information. The theoretical work consists of both face element and finite element numerical techniques. These are initially elastic solutions to provide comparisons of initial stress conditions around different mine panel geometries. A face element technique is developed to analyse mining panels where the length is considerably greater than the panel width. Large scale underground instrumentation provides detailed information on stress conditions, time-dependent deformations around mine roadways and strain distributions within pillars. This information, together with surface subsidence measurements and laboratory determined rheological properties, is used to provide more realistic boundary conditions for the numerical modelling of the mining layouts. The combination of the theoretical analyses and the measured data provide a set of design criteria for an optimum mining layout which satisfies the above requirements.Cleveland Potash Limite

Fine-Scale Movements of the Broadnose Sevengill Shark and Its Main Prey, the Gummy Shark

Information on the fine-scale movement of predators and their prey is important to interpret foraging behaviours and activity patterns. An understanding of these behaviours will help determine predator-prey relationships and their effects on community dynamics. For instance understanding a predator's movement behaviour may alter pre determined expectations of prey behaviour, as almost any aspect of the prey's decisions from foraging to mating can be influenced by the risk of predation. Acoustic telemetry was used to study the fine-scale movement patterns of the Broadnose Sevengill shark Notorynchus cepedianus and its main prey, the Gummy shark Mustelus antarcticus, in a coastal bay of southeast Tasmania. Notorynchus cepedianus displayed distinct diel differences in activity patterns. During the day they stayed close to the substrate (sea floor) and were frequently inactive. At night, however, their swimming behaviour continually oscillated through the water column from the substrate to near surface. In contrast, M. antarcticus remained close to the substrate for the entire diel cycle, and showed similar movement patterns for day and night. For both species, the possibility that movement is related to foraging behaviour is discussed. For M. antarcticus, movement may possibly be linked to a diet of predominantly slow benthic prey. On several occasions, N. cepedianus carried out a sequence of burst speed events (increased rates of movement) that could be related to chasing prey. All burst speed events during the day were across the substrate, while at night these occurred in the water column. Overall, diel differences in water column use, along with the presence of oscillatory behaviour and burst speed events suggest that N. cepedianus are nocturnal foragers, but may opportunistically attack prey they happen to encounter during the day

Moving in the anthropocene: global reductions in terrestrial mammalian movements

Animal movement is fundamental for ecosystem functioning and species survival, yet the effects of the anthropogenic footprint on animal movements have not been estimated across species. Using a unique GPS-tracking database of 803 individuals across 57 species, we found that movements of mammals in areas with a comparatively high human footprint were on average one-half to one-third the extent of their movements in areas with a low human footprint. We attribute this reduction to behavioral changes of individual animals and to the exclusion of species with long-range movements from areas with higher human impact. Global loss of vagility alters a key ecological trait of animals that affects not only population persistence but also ecosystem processes such as predator-prey interactions, nutrient cycling, and disease transmission

Review of Horizontal Surface Movements Due to Longwall Coal Mining Using Numerical Modelling

Strain is an important parameter for assessing the potential for impacts on surface features due to longwall mine subsidence, but it is also one of the most difficult parameters to predict. Whilst profiles of strain can be highly variable and irregular, zones of net compression and net tension generally develop above longwalls. By considering the relative horizontal surface movements over longer bay lengths, they become more regular and, hence, more predictable. Numerical modelling has been undertaken using universal distinct element code (udec) to assist with the development of predictive methods for the relative horizontal movements over the various zones above an active longwall. The numerical modelling was used to assess the effects of varying surface topography on the horizontal movements, including slopes, scarps, hills and small valleys. Predictive equations have been developed for the net compression within the sagging curvature zone and the net openings within the hogging curvature zones. These equations are consistent with the findings from reviews of ground monitoring data in nsw coalfields

Experimental protocol for stress corrosion cracking of rockbolts

A new laboratory facility designed and constructed at the University of New South Wales, aims to continue and offer a new approach to researching the phenomenon of the stress corrosion cracking. This new approach includes the use of full sized specimens, a specially designed frame, as well as a new loading regime, known as the Periodically Increasing Stress Test, to closely simulate the loading encountered by bolts in service. Coupled with a detailed water testing program to be undertaken at a number of partner sites, this new approach hopes to further increase understanding of stress corrosion cracking and its causes

Numerical simulation on borehole breakout and borehole size effect using discrete element method

Estimation of horizontal stress magnitudes from borehole breakouts has been an attractive topic in the petroleum and mining industries, although there are critical research gaps that remain unfilled. In this paper, numerical simulation is conducted on Gosford sandstone to investigate the borehole breakout and its associated borehole size effect, including temperature influence. The discrete element method (DEM) model shows that the borehole breakout angular span is constant after the initial formation, whereas its depth propagates along the minimum horizontal stress direction. This indicates that the breakout angular span is a reliable parameter for horizontal stress estimation. The borehole size effect simulations illustrated the importance of borehole size on breakout geometries in which smaller borehole size leads to higher breakout initiation stress as well as the stress re-distribution from borehole wall outwards through micro-cracking. This implies that the stress may be averaged over a distance around the borehole and breakout initiation occurs at the borehole wall rather than some distance into the rock. In addition, the numerical simulation incorporated the thermal effect which is widely encountered in deep geothermal wells. Based on the results, the higher temperature led to lower breakout initiation stress with same borehole size, and more proportion of shear cracks was generated under higher temperature. This indicates that the temperature might contribute to the micro-fracturing mode and hence influences the horizontal stress estimation results from borehole breakout geometries. Numerical simulation showed that breakout shape and dimensions changed considerably under high stress and high temperature conditions, suggesting that the temperature may need to be considered for breakout stress analysis in deep locations

A semi-quantitative coal burst risk classification system

Safety is the highest priority in the mining industry as underground mining in particular poses high safety risks to its workers. In underground coal mines, coal bursts are one of the most catastrophic hazards, which involves sudden and violent dynamic coal mass failure with rapid ejection of the broken material into the mine workings. Despite decades of research, the contributing mechanisms of coal bursts are still not completely understood. Hence, it remains challenging to forecast coal bursts and quantify their likelihood of occurrence. However, a range of geological and geotechnical factors are associated with coal bursts and can increase the coal burst proneness. This paper introduces a semi-quantitative coal burst risk classification system, namely, BurstRisk. Based on back-analysis of case histories from Australia, China and the United States, BurstRisk classifies the coal burst risk into three categories: low, medium and high risk. In addition, it allows mining engineers to modify the weighting of the selected factors based on specific conditions. The risk classification charts introduced are for both longwall retreat and development sections of longwall mining operations. This paper also provides a set of risk management strategies and control measures for effective coal burst mitigation. Keywords: Underground coal mining, Coal burst, Rockburst, Risk management, Safety, Semi-quantitativ

A review of cavability evaluation in longwall top coal caving

Longwall Top Coal Caving has been considered as one of the most effective technologies for the extraction of underground thick coal seams. A large number of studies on the applicability of Longwall Top Coal Caving into new mine sites have linked the success of its application to the geomechanical understanding of the cavability of the top coal. The paper aims to improve the knowledge of the top coal cavability evaluation. A range of parameters that affect the top coal cavability were first identified. Afterward, a number of cavability assessment methods and classifications were reviewed. The result is important in that it assists researchers in developing an advanced and reliable tool for the top coal cavability evaluation. Keywords: Longwall top coal caving, Cavability, Numerical modelling, Caving mechanism, Caving classificatio