Compacted Permeability Testing at the Forte Analytical Laboratory (FAL)

One of Forte Analytical Laboratory’s critical analytical testing services in the geotechnical and mining fields is the Compacted Permeability Test (CPT). FAL is proud to offer CPT in a wide range of cell sizes to analyze finely crushed material up to coarse run-of-mine (ROM) material. FAL is able to cater to a wide variety of requests, ranging from low loading conditions to simulations comparable to the deepest heap leach pads constructed in the world.

For the finest grain material, FAL can perform falling-head permeability testing (ASTM D5084) on in-situ samples taken using brass sampling tubes or on loose samples collected and compacted to a specified density prior to testing in cells from 1.5” to 6” in diameter.

For most CPT analysis performed at FAL, a dynamically loaded, constant-head permeability test procedure is used. Cell sizes available at FAL for this kind of testing are 6”, 10”, 20”, and 30” diameter units, which can handle material with maximum particle sizes of 1.2”, 2”, 4”, and 6” in diameter, respectively. These maximum particle sizes are based on a cell-to-particle size ratio basis of 5:1.

FAL has the capabilities to inform heap leach operations in addition to the ability to design and optimize for the entire range of crushed and ROM heap leach pads. Tests performed in the 6” cell make use of a 10-ton manual hydraulic press. Cells at diameters 10”, 20”, and 30” are tested with a 150-ton electric hydraulic press. Typical CPT procedures make use of at least 3 stage loads under each of which the applied load from the hydraulic press is held constant. The water level (head) is maintained just above the sample within each cell, and the water flowing out from the bottom of the cell is collected while the entire test is being timed. By making use of multiple stage loads, FAL creates a permeability rate versus loaded height curve that is used to make determinations about the flow characteristics of heap leach pad material and its leachability under increasing loading conditions on a heap leach pad. By this process, FAL can determine the loaded/compacted permeability rate of up to 6” material at an initial dry bulk density of 120 lb/cf at a simulated heap depth of up to 500 ft.

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