Potash Slope Stability using SVSlope

By Murray Fredlund

July 8, 2009

A project recently undertaken by students at University of Regina involved slope stability numerical modeling of potash tailings. The work involved two primary objectives:

• Use slope stability software to determine the factor of safety of one side of the waste pile, and
• Perform a sensitivity analysis to identify the safe terminal height and optimized volume that could fit within the current land restraints.

Saskatchewan is home to ten of the eleven potash production operations in Canada. Eight of the ten operations are conventional mines and two are solution mines. These mines result in the slurried deposition of Tailings Management Areas (TMA) which are subject to the natural processes of erosion and dissolution. Optimizing the lifespan of the TMAs is in the best interest of the mines and the purpose of the present study. Optimization of the present TMA can potentially avoid the problems with building a new TMA or lateral expansion of the current one.

It is the stability of the TMA which was the focus of the present slope stability project. The SVSlope™ software was selected for use in the present project due to the simplicity with which a sensitivity analysis can be performed. The software also implements comprehensive abilities to handle the unsaturated strength characteristics which can be a significant contributing factor to the calculation of the factor of safety (FOS). The comprehensive array of critical slip surface searching methods also simplified the determination of the true minimum FOS. The geometry for one of the models may be seen in Figure 1, above.

The standard method of slices equilibrium method was used in the present study to determine the FOS. The tailings pile was built in the SVSlope software as a series of lifts with benches between various lifts. The benches were designed to achieve an optimal FOS. An aerial view of the TMA may be seen here, in Figure 2.

The numerical modeling performed at the University of Regina was successful in i) determining a factor of safety of the critical side of the tailings pile, as well as ii) determining the optimal height of the pile. It was also determined in the SVSlope software that the stability of all tiers is not the same. The critical tier could be identified in the software and isolated for further examination. The sensitivity analysis was performed in the SVSlope software and allowed correlations between bench width / height and the factor of safety to be determined.

If this numerical modeling is of interest to you please contact Dr. Shahid Azam at the University of Regina (Shahid.Azam@uregina.ca).