1.0 N
The object of this paper is to discuss those aspects of open pit mine design which are affected by geotechnical factors. The temptation exists for some practitioners of geotechnical engineering to believe that this relatively new engineering discipline is the 'be all and end all of mining., In the opinion of the authors, this is fallacious but, as our ability to put numbers to the behavior of rocks and soils improves, it is clear that geotechnical engineering will become an integral and important part of designing and operating mines successfully. Open pit mines in the context of this paper also includes open cast mines, where the 'ore" is extracted and the waste material is immediately replaced or backfilled in the mined portion of the pit. Open pit mines operating today move from very small tonnages a day to in excess of 400,000 tons per day. Several mines are operating and are being designed to capital expenditure for such projects in some cases exceeds $5,000,000 dollars and in a few cases will exceed one billion dollars. The size of this investment means that financing will have to be provided from banks or joint partnerships. This financial environment means that planning will be carefully scrutinized by experienced representatives of financial institutions or other mining companies. All too often a project has been put in jeopardy because the personal desire of one or two men to make a project proceed has caused incomplete planning or perhaps in some instances deliberately leading observers down the garden path. In our opinion the day is rapidly arriving when the quality, logic, practicability and completeness of the planning will make the difference between securing financing or not and, in the cases of existing open pit mines, of the difference between survival and closure. Feasibility studies are often extremely lengthy documents and this is sometimes regarded as domonstrating completeness in planning. Brief and precise summaries are the measure of the quality of the project management. Open pit mine design is a significant portion of project management and we have attempted in this document to demonstrate where geotechnical engineering can be useful in improving mine design. Pit planning must be both economically sound and economically executed. The following table outlines what we believe are good guidelines.
(Table available in full paper)
Mine planning costs for various projects have in the past varied from less than 1% to greater than 7% of the initial exploration or project capital expenditure of the project. These costs have included drilling, metallurgical, geotechnical, computer costs and manpower. In comparison the oil industry typically spends as much as 10% in engineering feasibility studies. It is essential to evaluate at any stage in mine planning the accuracy required in any particular part of the study and to weigh this against the sensitivity to the overall project. For example, it is pointless to go to great lengths to work out schedules for trucks and shovels, if the size of the orebody is not defined realistically within 50%.
