Abstract
Nowadays, for a number of reasons, many open pit mines are considering a transition from Open Pit (OP) to Underground (UG) to remain competitive. In OP-UG transition, UG operation is operated simultaneously with the OP operation for a certain period of time. Guidelines for the simultaneous operation of OP and UG are very difficult to establish, as there are very few case studies available. Yet, because of the OP-UG interactions; the operation has a higher safety, technical and management requirements than the OP or UG methods when considered separately. In Vietnam, Cao Son is one of many OP mines, which decided to change the operational system from OP to UG. Simultaneous operation started in 2015 and will be conducted until 2030 when the OP mine Cao Son ends its mining activities. In this paper, selected geomechanical considerations of the simultaneous operation are presented. A number of numerical modelling calculations using finitedifference software with code FLAC were carried out for calibration process, slope stability analysis and the OP-UG interaction analysis for the Cao Son – Khe Cham II–IV mine. Based on the results obtained from numerical modelling, the geomechanical assessments of simultaneous operation Cao Son – Khe Cham II–IV are discussed in this paper.
Highlights
Over time, open pit mines tend to go deeper and become larger
It is necessary to carry out more research and analysis on slope stability of open pits affected by underground mining and, due to the different geological conditions and the technology application, any such case should be analyzed individually
Obtained results indicate that UG exploitation in coal seam No 9 influence slightly the slope stability of the 2020 pit and the left-right UG operation is recommended
Summary
Open pit mines tend to go deeper and become larger. with the increasing depth of exploitation, there are a number of difficulties that make further exploitation unsafe and/or unprofitable. Underground operation causes subsidence, slope movements, discontinuous deformations and change of hydrogeological conditions. In the case of underground operation located below the open pit mine, slope strain. The negative OP-UG interaction cases [3,4,5] provide a clear warning as to the possible impact of underground mining on open pit mines. It is necessary to carry out more research and analysis on slope stability of open pits affected by underground mining and, due to the different geological conditions and the technology application, any such case should be analyzed individually. The OP mine Cao Son is decided to change the operation system from OP to UG (Khe Cham II–IV). Based on the results obtained, several geomechanical assessments are presented as a case study of Cao Son – Khe Cham II–IV
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