OPERATIONS
Once pore pressures, measured by piezometers, are plotted as
lines of equal head (h), known as equipotentials, the pressure
gradient of the slope will be like Figure 2.
Pore pressures can be measured using pressure transducers,
typically the sealed vibrating -wire point type piezometers,
grouted into coreholes drilled into critical sections of the slopes
of the tailings dam retaining walls.
The water balance of a tailings dam is affected by the rainfall
input to its pond and any surface runoff entering the dam
foundations from upstream. The groundwater levels around,
below and upstream impact on the water balance of the tailings
dam and need to be monitored and managed to increase
safety. Each dam is unique and therefore requires a bespoke
monitoring network, designed by a qualified hydrogeologist,
based on a full understanding of the water inputs, both surface
and underground.
Figure 2: Distribution of pressure gradients within a slope of a tailings dam
(Adapted Morton et al 2008).
Figure 3 shows the layout of an accurate monitoring network
around an individual tailings dam in plan.
An accurately instrumented tailings dam will include
monitoring of:
• Rainfall;
• Pond levels;
• Upstream surface and groundwater flows and pressures;
• Downstream surface and groundwater flows and pressures;
and
a tailings dam is essential to the understanding of the main
factor which controls tailings dam stability. Reducing pore
pressures by drainage of pumping will increase safety and if
implemented early will prevent failure. This strategy is far more
accurate and successful than the simple monitoring of slope
movement. When a slope moves it is often too late to reverse
the imminent failure, intervention by monitoring and then
active management of water pressure can prevent failure before
a catastrophic event.
• Pore pressure monitoring within all the tailings dam’s
slopes.
This data is converted to information and then resultant plots of
pressures can be used within dashboards to review the actual
pressures compared to the required pressures. Trends that
show increasing pressure can be used to implement pressure
reduction actions such as drainage or pumping. Dashboards
can be shared to inform decision makers of increasing pressures
which can then be reduced by increasing drainage of the
unstable slope. The information can be transmitted by satellite
to local and remote decision makers.
Accurate and well-distributed pore pressure monitoring of
About the Author
Dr Kym L Morton is an international expert on groundwater
and mining hydrology. You can contact Dr Morton at:
[email protected].
References:
1. Morton et al (2008) Importance of pore pressure monitoring in high
walls.
2. Morton KL (2019) The use of pore pressure monitoring for accurate
tailings dam monitoring.
Figure 3: Tailings and upstream monitoring (adapted from Inmarsat).
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