Side Slope Seepage Investigations

Side Slope Seepage Investigations

Article by: Dr. Dale Rucker | Chief Technical Officer | hydroGEOPHYSICS

For mining engineers and leach pad supervisors, informed slope design of heaps and dumps is essential for minimizing failure risk, maintaining safe stacking, and maximizing ore output and profit.?Design reliability begins with understanding the hydrodynamics and potential risks associated with side slope seepage.?Failure to do so can lead to disastrous consequences from slope failure, the genesis of which can typically be traced back to the formation of side slope seeps.?Geophysical methods such as electrical resistivity tomography (ERT) are capable of detecting the adverse hydraulic conditions associated with seeps within heaps and leach pads in their earliest onset phase.?Early detection is key for initiating, action, and upending adverse conditions that can lead to slope failures.

Geophysical methods such as electrical resistivity can detect adverse hydraulic conditions associated with seeps within heaps and leach pads.

Electrical Resistive Tomography is an electrically based imaging method that measures the electrical field strength during current flow into the ground.?The strength of the electrical field is proportional to the resistivity of the earth, which in turn is affected by subsurface saturation.?The mining industry widely uses electrical resistivity tomography in applications such as mineral exploration.?HGI has taken the innovative approach of applying ERT to investigate the adverse hydraulic conditions which give rise to seep formation within heaps and dumps.

Electrical resistivity profile over a waste rock pile

The figure shows low resistivity values for areas of high pore pressure in a pile. The saturated regions indicate decreased resistivity values (dark blues and purples) that developed due to compacted or clayey material preventing drainage.

HGI conducted an electrical resistivity profile over a waste rock pile to understand subsurface flow regimes that may be causing side slope seepage. The figure above shows low resistivity values for areas of high pore pressure in the pile. The saturated regions indicate decreased resistivity values (dark blues and purples) that developed due to compacted or clayey material preventing drainage. Although some drainage does occur, it is far too low to accommodate the surficial recharge.

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The genesis of seeps can be traced back to compacted ore.?Compacted ore prevents drainage, creating perched water tables.?Over time excess pore pressures building within saturated ore on or near slopes can lead to failure.?Fortunately, saturated ore is easily?mapped with ERT technology.?Because ERT surveys are conducted strictly from the surface, they do not require heavy equipment.

Saturated ore is easily?mapped with electrical resistivity technology.

HGI offers a full suite of in-house capabilities to meet the needs of mining professionals.?By walking projects from the planning stage, to data acquisition, data processing, and interpreting results, HGI will maintain a timeline that meets the critical needs of your schedule.?We offer solutions-based approaches to help mitigate the impacts of side slope seeps so that your facility can continue to operate safely, effectively, and profitably.

Follow the link below for more information on ERT’s use for defining side slope seeps.?While you are at it, connect with us on LinkedIn.?Call us up if you have a project where ERT could benefit you or your client!? We are passionate about what we do and honest with the applications and limitations of geophysical technologies.?

About the Author: Dr. Dale Rucker | hydroGEOPHYSICS

Dr. Dale Rucker currently acts as the Chief Technical Officer (CTO) for HGI. He is a geophysicist and hydrogeologist with a strong background in engineering and publishing. As CTO, Dr. Rucker has been instrumental in bringing to HGI new geophysical-based technologies to solve complex problems involving water resource, mining, engineering, and geotechnical issues. Over the past 15 years, he has published over 40 peer reviewed papers and book chapters in subjects of mining, karst, hydrogeology, and geophysics. Dale holds a BS in Mechanical Engineering, MS in Civil Engineering, and a Doctorate in Hydrology and Water Resources from the University of Arizona.