Advanced Computational Analysis of Roof Stability in Highwall Phosphate Mining Operations

Abstract:
Strip mining is typically preferred for near-surface, tabular deposits such as phosphate. 
Khouribga, home to Morocco’s largest phosphate deposit, contributs significantly to the 
nation’s phosphate output. However, a slight dip in the phosphate deposit suggests that strip 
mining may become less viable in the future. To sustain phosphate production efficiently, 
transitioning from surface to underground mining through highwall mining could be an 
effective solution. This method, involving the recovery of phosphate using continuous miners, 
necessitates stable roof conditions.
To evaluate roof stability in highwall mining, both with and without web pillars, we will employ 
a three-dimensional finite difference method. Firstly, field rock mass properties, including joint 
frequency, persistency, infills and orientations and mechanical parameters, will be determined 
for inclusion in the numerical model. The generalized Hoek-Brown failure model, in 
conjunction with the Geological Strength Index (GSI), will be utilized to analyze rock mass 
behavior. For intact rock behavior, triaxial tests will be conducted to acquire Hoek-Brown 
failure parameters. These parameters will inform the construction of realistic 3D models using 
FLAC3D software, enabling the simulation of various underground working scenarios to 
identify the optimal mine layout that ensures high production rates and minimizes roof stability 
issues.
An economic analysis will also be conducted to assess the feasibility of this method. This 
analysis will help in optimizing the dimensions of highwall mining parameters and selecting 
the best scenario through the Mineable Shape Optimizer (MSO). This planning tool will 
additionally aid in forecasting the recovery and dilution rates associated with the 
highwall mining method.
Keywords:
Highwall mining, Phosphate, Khouribga, Roof stability, GSI, Rock mass classification, HoekBrown failure model, Economic analysis, MSO