Abstract
The monitoring and measurement of the phreatic surface is a key input to the assessment of stability of tailings dam embankments. The most common method of physical assessment of the phreatic surface is by the installation of a number of piezometers arranged in lines (sections) at intervals along embankments with the phreatic surface interpreted (usually in two dimensional sections) between the measured points. As part of routine tailings dam management, it is usual for a trigger value (or values) to be assigned to each piezometer and defined actions taken by the operators in the event a trigger value is recorded. However, in reality (in most cases) there is no unique trigger value for each piezometer (as a range of phreatic surfaces would have a similar factor of safety against instability) and as a result either lower bound values are used (causing an increased chance of reaching a trigger) or potentially under-conservative values are adopted. This paper details a method that aims to solve the issues described for the triggers by pre running stability analyses with a range of plausible phreatic levels within the TSF embankment. The stability outputs are used to create a database containing the phreatic levels and the corresponding Factor of Safety (FoS) for a range of phreatic surfaces, which can be used to rapidly assess site measurements. The processes utilises a Python script to generate thousands of phreatic surfaces, PEST scripts to automatically run the stability models in SLOPE/W, and another Python script to collate the results into a database. The paper also shows how the database can be implemented in a spreadsheet interface to allow rapid assessment of a given result set. This approach is not intended to replace detailed analysis but will provide rapid screening at a more accurate level that is typically employed. The automation being the key to making this approach viable.
