Author ORCID Identifier

https://orcid.org/0009-0001-3847-5939

Semester

Fall

Date of Graduation

2025

Document Type

Thesis

Degree Type

MS

College

Statler College of Engineering and Mineral Resources

Department

Civil and Environmental Engineering

Committee Chair

John Quaranta

Committee Member

Onur Avci

Committee Member

Harold Russell

Abstract

As part of ongoing efforts to establish a domestic Rare Earth Elements (REE) supply chain, Hydraulic Preconcentrate (HPC) generated at the Horseshoe Bend (HsB) treatment plant was produced and evaluated as a potential feedstock source. Following adjustment of the site’s clarifiers to the required pH set points, HPC was collected and pumped into 24 geobags. These geobags were passively dewatered to raise the total solids content. The evaluation included three geobag types: woven geotextile, composite (woven and non-woven), and geobags enhanced with Capillary Channel Fiber (CCF) (Bird, 2024). Hydraulic Preconcentrate (HPC) material is collected through efforts to contain and properly handle AMD. Collection means consist of geobags used for the dewatering process which retain solids within the AMD. Research on the strength of this HPC material is obscure, provoking the question of the strength behavior of this uncommon material.

The geotechnical engineering department does not currently have a course offered that focuses solely on triaxial compression testing, with means of running tests as students. This was mainly a result of outdated operation manuals for the Sigma-1 triaxial machines present in the lab. The department plans on offering a triaxial compression test course for the graduate level once operation manuals are available.

Using the HPC material collected from the Horseshoe Bend (HsB) treatment plant in Butte, Montana, the study objectives are to: (1) investigate the triaxial machine and reputable sources for proper usage and correctness, (2) develop operation manual and teaching videos for triaxial compression testing using Sigma-1 equipment, and (3) determine strength and pore pressure characteristics of the HPC material.

The first objective was met by compiling available documents for the correct setup of the machinery investigated by former graduate students; testing procedure was determined through Sigma-1 software documents and the trial-and-error method. Trial tests were run using Shelby tube samples to determine accuracy, which found an internal friction angle of the medium plastic clay to be 28 degrees. This was evaluated against the Soil Mechanics in Engineering Practice textbook which gave an acceptable range for similar medium plasticity soils to be between 26 and 32 degrees. The second objective was met by determining the correct procedure for testing on the specific Sigma-1 machine by running several tests with it. Once accuracy was obtained, the procedure was detailed and formatted efficiently for use in a classroom environment, with the addition of teaching videos explaining each step in the procedure. The third objective was met by completing isotropically drained and undrained triaxial tests on the HPC material to determine the shear strength and pore pressure dissipation characteristics of the material. This was conducted to determine geobag stacking capabilities and efficiencies for optimal strength and pore pressure dissipation.

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