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Heap Leach Pads--The Importance of Proper Testing, Interpretation, and Analysis of Soil Liner Geomembrane Interfaces

Author: Guillermo Barreda, Luis Chahua
Conference: Heap Leach Solutions 2014
Date: November 10-13, 2014

The design of heap leach pads involves a variety of components. One of the main components for these structures is the leach pad liner system, where a low-permeability soil is normally used in combination with a geomembrane to reduce seepage losses. Although this combination of materials has been shown to effectively reduce rates of infiltration, the soil liner-geomembrane interface presents a challenge to designers since it incorporates a “weak layer” into the system, which has negative effects on the physical stability of the structure.

Usually, the effects produced by the soil liner-geomembrane interface govern the stability of the heap leach pads; therefore, it is critical to characterize its behavior by (a) proper sampling and testing— for example, taking into account the design loads that will be imposed by the heap; (b) proper interpretation—for example, taking into account the nonlinear behavior of the interface; and (c) proper application of the results to the analysis—for example, assessing the use of post-peak and large displacement values. Lastly, verifications must be carried out during construction to ensure that the assumptions made during the design are implemented on site.

Although there are papers that discuss these issues individually, the intention of this paper is to present from the designer perspective the key variables to consider at each stage (sampling, testing, interpretation, analysis, and verification during construction). The approach will take into consideration an interface-testing database with more than 10 years of test results, and the experience gained in the interpretation and analysis of these results for heap leach pad projects developed in Peru.

Oversimplification of decisions related to testing, interpretation, and analysis of the soil liner-geomembrane interface can lead to potential economic, environmental, and safety impacts to the project, as well as an increase of the risk levels of the structure. Therefore, the implications of identification and discussion of the variables at each of these stages are important not only to designers, but also to other parties such as clients, manufacturers, and construction companies.

 

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