## 3 Application and Illustration of the Proposed CRITIC-GRA Model  
### Project Overview  
The proposed CRITIC-GRA model was illustrated in details based on its application to a newly built underground iron mine in Anhui Province, China. The 1# main orebody of the mine is a sedimentary-metamorphic iron deposit with main geological formations ranging from \(-200\) m to \(-550\) m, with an average dip of \(85^{\circ}\), thickness of \(35\) to \(70\) m, and a strike length of more than \(2\) km. The ground surface of the mine is flat at an elevation of approximately \(+50\) m. The long-hole stage open stoping with subsequent backfill mining method is the primary method to excavate the orebody, with the main levels designed to be mined at \(-500\) m, \(-440\) m, \(-380\) m, \(-320\) m, \(-260\) m and \(-200\) m in a bottom-up mining sequence. Currently, mining activities are concentrated on the primary stopes in the bottommost level \(-500\) m\(\sim\)\(-440\) m, while the other upper levels are under the engineering development period.  
The intention of the double stage open stoping mining method for the primary stopes was originally proposed by the mine manager because the mining efficiency and stoping production capacity will be substantially improved if the stope height can be doubled from the current \(60\) m at the \(-500\) m\(\sim\)\(-440\) m level to \(120\) m at the \(-500\) m\(\sim\)\(-380\) m level. Andthe increased ore extraction volumes through the current mucking engineering structures at \(-500\) m level will alleviate the financial pressure previously caused by the investment in mine construction. In addition, the following cemented backfill operations of the primary stope voids can build up a vertically intact man-made pillar instead of two separated parts at the middle \(-440\) m level, which is beneficial to the adjacent secondary stopes mining.  
Previous investigations into the rockmass quality of the mine have provided preliminarily evidence that the intact and stable rockmass (most regions with Grade I and partly Grad II classification) offers the possibility to enlarge the stope void height from 60 m in the design report to 120 m. In addition, a further expansion of the stope width from the previously designed 14 m could be considered. The expansions of the stope dimensions will affect the continuous stopes division layout along both the vertical and the strike directions of the orebody. Despite a predictable increase on stope production capacity and a reduction in tonage costs under enlarged stope dimensions, a consequence of increased safety risk of the enlarged exposure on side walls and roof around the stope void could also occur. It is a key option for the mine to adjust the stope dimensions reasonably based on the practical rockmass properties to striking an optimal balance between enlarged stope stability, increased mining production capacity and costs.  
Therefore, the typical stope dimension parameters including length (\(L\) = 40, 45, 50, 55, 60 m), width (\(W\) = 15, 20 m) and height (\(H\) = 60, 120 m) of the illustrated iron mine were combined to build up preset schemes to be input samples in the proposed CRITIC-GRA optimization process. As can been seen in Table 1, there are 20 preset schemes with different stope dimensions. The aim was to find out a relatively optimal scheme of them with an integrated stability probability via the updated Mathew graph and FLAC3D numerical simulations, and the estimated mining economic index for stoping production capacity and costs. The results can be an objective and reasonable reference for the decision-making of the mine designers or managers.