Open Cut » Overburden Removal
Caterpillar Command for Dozing is a Semi-Autonomous Tractor System for D11T dozers that can perform bulk dozing. The first deployment of this technology was at Black Thunder Coal Mine in Wyoming where it was demonstrated to be capable of executing push-to-an-edge bulk dozing as part of a dragline strip mining project.
This report describes collaborative research undertaken by the University of Queensland and Caterpillar to extend Caterpillar Command for Dozing so that is capable of pivot-push dozing.
The report is framed against the context of the need to understand how to best choreograph the sequence of cuts, pushes, and dumps performed by an autonomous dozer for bulk move pivot push dozing so that the material moved by the is dozer is moved as efficiently as possible. Difference in opinion among operations about how best to pivot push exists and this report looks to shed some light on this question, accepting that in different circumstances different methods might be preferred.
The report describes the common variants of pivot push dozing in use in the Australian coal sector and presents a software framework developed to simulate pivot push dozing operation. This framework takes as its input a pit geometry determined by aerial survey, the characteristics of the material to be pushed, and the attributes of the bulldozer machinery. The framework simulates the movement of material under the action of a dozer and computes a push sequence for efficient material movement.
This simulation framework allows, among other things, an expected effective-time productivity trajectory for the push to be computed which gives the volumetric rate at which material is moved to prime. The simulation framework is validated using experimental data collected for a manual push operation. Computed productivities are shown to match well to actual productivities determined by volumetric measurements obtained by aerial survey.
The question of which pivot push method makes best use of the effective dozer time is explored through the simulation framework. The report gives comparative productivity results for three pivot push variants in current use across Australian mines. Results indicate the preferred method for pivot push dozing should be to tip-head till the void is levelled followed by either back-stacking or tip-heading the remaining material uphill. The report goes on to explore how well the semi-autonomous dozer technology performs. The metric used for evaluation is the effective time productivity (ETP): the cumulative volume of overburden moved to locations beyond the pivot-point as a function of time the bulldozer spends in effective operation. Predictions of expected ETP computed by the simulation framework provide a reference against which actual dozer productivity can be evaluated for a specific overburden profile and material properties. The report compares the measured ETP acheived by the semi-autonomous technology at the time of its initial deployment and then again after six months following further technical development. The initial productivity trial was undertaken at a time when operators were still in process of learning how to use the system. This initial trial showed the semi-autonomous technology achieved 85% of expected ETP. Reasons for the gap between expected and actual operation were identified and addressed. These included operator familiarity with the technology as well as technology improvements to address identified issues.
A second productivity trial conducted after improvement to the system showed the semi-autonomous technology has an ETP similar to that for manual operation.
The project has demonstrated that semi-autonomous pivot-push dozing in technically feasible and its productivity can match manual operation.
The significance of this work to the Australian coal industry is in supporting the realization of technology for semiautonomous pivot push operations and also in providing methods for evaluating the effectiveness of those operations.