Date of Award

Spring 5-4-2024

Degree Type

Thesis

Degree Name

Master of Science in Geoscience: Geological Engineering Option

Department

Geology

Committee Chair

Mary MacLaughlin

First Advisor

Curtis Link

Second Advisor

Abhishek Choudhury

Abstract

In this study, stress and strain measurements from unconfined compression tests were used to determine the peak stress, yield stress, Young’s modulus, and Poisson’s ratio of 20 specimens representing three lithologies (sandstone, norite, and argillite-quartzite mix) from Idaho and Montana. Along with traditional strength and deformation parameters, crack initiation (CI) and crack damage (CD) values were also interpreted, corresponding to the stress levels associated with the formation and coalescence of microcracks as a specimen is exposed to increasing stress levels. Acoustic emissions (AE) data were collected along with traditional stress-strain data as this has become a popular method for interpreting CI and CD.

Three approaches were used to determine CI: interpreting the departure from linear of the plot of lateral strain vs. axial stress both manually and with the lateral strain response (LSR) procedure and using the cumulative acoustic emission hits (CAEH) method to identify a sharp increase in acoustic emission activity associated with crack formation. The LSR procedure and CAEH method were implemented as Matlab modules. CI values from the CAEH method had a large variation, even between AE sensors on the same specimen. Although when averaged the CAEH CI values were only slightly above the range in previously reported literature. CI values produced by the CAEH method also had a higher variation than the LSR and manually determined stress-strain measurements, which were generally in good agreement with each other. CI values from both stress-strain approaches aligned closely with CI values from previously publish data. The relationship between the yield stress and CD was also examined, as anticipated, CD and yield stress were in good agreement, although CD values were generally higher than the yield stress. Young’s modulus and Poisson’s ratio values were determined from the stress-strain curves to characterize the deformation parameters of the three lithologies. The values observed in this study compare relatively well to values in reported literature.

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