Determination of slope angle is one of the most important parameters in open PIT mine design. With low slope angles, stripping is considerably increased. On the other hand, selection of high slope angles may reduce safety and causes failure. Therefore, to prevent slope failure and high stripping, a compromise is necessary to select an OPTIMUM slope angle. There are several methods of analyzing the stability of open PIT SLOPES such as limit equilibrium methods, empirical methods and numerical methods. In this paper, FLAC software has been applied to determine the overall slope angles in the different parts of Sungun copper mine. For analyzing the slope, five vertical sections with a proper coverage of all parts of the mine, were considered. For the aforesaid sections on the static loading, stability analysis was performed for different slope angles and then with the help of regression analysis a relationship was developed between safety factor and angle of slope for each of the sections separately. In this research work, on the basis of geo-mechanical characteristics of rock mass, a factor of safety of 1.2 was selected. On the basis of obtained results, mine slope in the south and south-west was detected to be critical. Based on this analysis, slope angle of the mine, in the south and south-west parts and for the north and north-east part, was considered to be 25 and 37 degrees respectively.Sensitivity analysis was fulfilled for each section to study the role of cohesive strength and internal friction angle. It was considered that section 4800 (west) and section 4800 (east) respectively have the highest and lowest sensitivity to variations of cohesion. Also it was seen that section 4800(east) and section NE-SW respectively have the highest and lowest sensitivity to variations of internal friction angle.

With the advent and wide spread use of computers a number of algorithms have been developed to determine the OPTIMUM ultimate PIT limits in open PIT mining. The main objective of these algorithms is to find groups of blocks that should be removed to yield the maximum overall mining profit under specified economic conditions and technological constraints. The most common methods are: Lerchs and Grossmann algorithm based on graph theory, the Korobov algorithm, floating or moving cone method, moving cone II and dynamic programming. Among these, the Lerchs-Grossmann algorithm is the only method that always yields the true OPTIMUM PIT. The disadvantages of the algorithm are complexity of the method and require more computing time than other methods to find out OPTIMUM PIT outline. The floating cone approach which does not yield a true OPTIMUM PIT in some cases is the most popular and simplest method and requires significantly less computing time than any other method to reach a solution. The moving cone II has been developed by Wright to overcome the shortfalls of the floating cone method. In this paper the moving cone II has been evaluated for being as a true OPTIMUM open PIT design method and also two algorithms has been proposed for modification of this method. For this purpose C++ computer programs have been developed under Windows operating system for these algorithms and their results are compared with the Lerchs and Grossmann method, which is the true OPTIMUM open PIT design algorithm. The outcomes show that these algorithms are able to produce good results.

This paper has paid to select the OPTIMUM dewatering system of Sechahoun open PIT mine. In order to chose the OPTIMUM dewatering system for this mine, hydrogeologic studies along with exploration drilling have been carried out and the obtained data has been applied for modeling of groundwater (using MODFLOW software, version PMWIN 5.3), in different conditions of the PIT depths. For the calibration of model, the hydraulic conductivity has been calibrated, in steady state condition, by adjusting the computed and observed groundwater level. In this study, the model of groundwater flow has been obtained then according to this model, the usability of two alternative dewatering systems (pumping wells and drainage tunnel) has been investigated. According to this study, pumping well system has been suggested as the OPTIMUM dewatering system, in technical and economic point of view. In this order, during the first 15-year mining operation, 5 pumping wells, and during next 10 years, 6 pumping wells have been suggested to ensure the existence of dry mining operation environment.

The Lerchs and Grossmann algorithm is a rigorous technique Based on Dynamic Programming, developed for optimization of open PIT limits. This algorithm guarantees the true OPTIMUM solutions in 2D sections, but is may be used only for PIT slope constraints of 1:1, 2:1 or more. In circumstances, where the geomechanical conditions impose less SLOPES such as 1:2, an adjustment of the block sizes and reconstruction of the block model is needed. A new algorithm is introduced in this paper to overcome this shortcoming. The conventional block model is transformed into an intermediate and a final block model to reflect the PIT slope constraints. Then the modified Lerchs and Grossmann algorithm consisting of a recursive formula with two criteria is implemented on the final model. Using this algorithm, there is no need for reconstruction of the block model.

Dynamic slope stability in open-PIT mines still remains a challenging task in the computational mining design. Earthquake and blasting are two significant sources of dynamic loads that can cause many damages to open-PIT mines in active seismic areas and during exploitation cycles. In this work, the effects of earthquake and blasting on the stability of the NW slope of Chadormalu mine are compared by a numerical modeling method. The dynamic results show that the maximum displacement under earthquake and blasting loads within the slope are 844 mm and 146 mm, respectively. According to the shear strain results, both the earthquake and blasting waveforms are destructive, while the earthquake waveforms cause more damages to the slope. Moreover, the deterministic and probabilistic seismic hazard analyses are carried out to assess the seismicity of the mine area. The experimental results indicate that the maximum values for the vertical and horizontal accelerations are 0. 55 g and 0. 75 g, respectively. The maximum calculated acceleration is then scaled to the selected earthquake accelerograms. In order to show the effective impact of the established scale, the model is executed using the original accelerograms. The results obtained show that the established scale prevents overestimation and underestimation of the displacement and strain. Therefore, applying scaled accelerograms in a dynamic slope stability analysis in mine SLOPES leads to more reliable and robust results. The overall results show that a strong earthquake causes plenty of damages to the slope, and consequently, interrupts the mining cycle. Hence, the seismic study and dynamic slope stability should be considered as a part of the computational mining design.

The most important issue, in the case of deposits with high axial expansion, is determining the "OPTIMUM transition depth from open-PIT to underground mining (OTD)." The main objectives of the research are providing a framework-based method (mathematical model) to determine environmental costs and propose an optimization trick for combined mining options and transition planning (OPTIMUM transition depth), development, implementation and validation of the optimization framework based on the Mixed integer linear programming (MILP). The result of the MILP is to determine the most suitable mining option(s) for the mining of the ore and to schedule the extraction in such a way as to maximize the NPV. Python and MATLAB programming platforms were chosen to implement the MILP, and a large-scale meta-heuristic optimization solver was presented for this research. The MILP planned the Songun copper mine reserve with sequentially combined mining over a mine life of 13 years. The OPTIMUM transition depth from open-PIT to underground mining was 950.

Environmental concerns on mining activities started near the end of the 20th century and are still underway. Due to mining activities, the adverse environmental impact has been significant throughout the history of mankind, whereas the minerals produced by mining activities have been providing the basis for human civilization. The legacy of past mining practices is large quantities of acid generating waste materials and tailings that caused abounding acid mine drainage problems. Modern mining environmental management tends to focus on concerns over the impact of waste disposal on surface primarily in the form of tailings and waste materials structures. Sustainable development principles are being increasingly applied by mining companies in developed and developing countries. Operating costs per unit of operation is recognized to be one the most important sustainable mining practice indicator and cut-off grade is considered to be a well-founded representative for this indicator. In this study, a developed model for OPTIMUM cut off grades is presented that not only relies on economical aspects but also minimizes adverse environmental impact in the form of acid mine drainage elimination or mitigation against the approach of postponing the restoration/reclamation activities at the end of the project’s life.