The results of a series of research studies since 1984 at The University of Queensland into dragline bucket performance identified the potential benefits of a new bucket geometry. Original performance testing of the new bucket geometry (UQ1 bucket) produced a thirty per cent reduction in filling times with the application of twenty per cent less energy when compared to conventional bucket performance. Although the results of the testing were encouraging, it was identified that there were possible problems with the scaling of the buckets. In particular, the weight of the scale buckets was found to be incorrect. A program of testing was developed to resolve the question of scale modelling with regard to soil-machine interaction and to further develop the UQ 1 bucket design.
The testing program was broken into three distinct stages with the first of these involving investigation into the scale modelling theory applicable to dragline bucket scale performance. Through the use simplified digging implements such as single teeth and backless buckets, the critical factors with regard to scale modelling were isolated and quantified. The most important finding of this stage of the investigation was the fact that a consistant scale factor of three was applicable for all materials provided that they were in an air dried condition. This allowed all future testing to be undertaken at a scale factor of three due to the air dried nature of all materials.
The second stage of the test program involved confirmation of the original test results and further development of the UQ 1 bucket design. The existing buckets were modified to reflect the correct scaling strategy and the series of tests conducted by Rowlands (1991) repeated. Results indicated that the UQ 1 bucket did in fact fill faster and use less energy than the standard bucket design. However, the difference was not as great as was found in the original test program. Further investigation into the bucket length to width ratio was accomplished through the use of false backs in the existing buckets. These results, in the quantitative sense, were inconclusive, but qualitatively provided an indication that a bucket between the two existing designs would provide better results. Why the false back tests failed to provide quantitative results is not known.
Stage three of the test program involved construction of the third bucket and subsequent testing in a variety of materials. Materials included the two original materials and four overburden materials from operating open cut coal mines in Central Queensland. Results demonstrated that the material properties play a large role in determining the performance of the dragline bucket however, the bucket design is still the most important factor. Results obtained indicate that the new (UQ2) bucket is as good or better than the UQ1 bucket developed by Rowlands (1991) in the original test work.
Further test work is required to identify the optimum bucket shape and even more extensive testing is required to determine the optimum design and set up of the dragline bucket for each material to be excavated. Scale model test work can play a large part in both of these processes due to the relatively inexpensive nature of the test work.