JRMGE / Vol 16 / Issue 12

Article

Expanded pore-emanated cracking model for brittle failure of sedimentary rocks under triaxial compression

Esraa M. Alomari, Kam Ng, Lokendra Khatri

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a Department of Civil and Architectural Engineering and Construction Management, University of Wyoming, Laramie, WY, 82071, USA
b Kiewit Corporations, Colliersville, New York, NY, 13747, USA


2024, 16(12): 5050-5060. doi:10.1016/j.jrmge.2024.01.019


Received: 2023-09-10 / Revised: 2023-12-07 / Accepted: 2024-01-30 / Available online: 2024-05-24

2024, 16(12): 5050-5060.

doi:10.1016/j.jrmge.2024.01.019


Received: 2023-09-10

Revised: 2023-12-07

Accepted: 2024-01-30

Available online: 2024-05-24


Abstract:

Brittle fracture and its relationship to deformation and strength have been a fundamental area of research in rock mechanics. This paper presents an expanded pore-emanated cracking model to better understand the fracture behaviors and predict the compressive strength of sedimentary rocks. This proposed model is developed to account for a triaxial compression condition using the triaxial compression test results on sandstone, limestone and siltstone samples from Wyoming, USA and experimental data on sedimentary rocks collected from published literature. The normalized critical crack length is determined from the proposed model through which the peak compressive strength is estimated when the stress intensity at the crack tip reaches a critical value called the fracture toughness. Results indicate that the rock porosity and pore radius have an inverse relationship with the compressive strength. Adopting the porosity-permeability relationship, the pore radius is calculated in terms of porosity and grain size. Next, the effect of grain size is implicitly included in the model and negatively correlated with the compressive strength. Moreover, a new approach is proposed for the estimation of fracture toughness based on the pore radius and confining pressure. The predicted compressive strengths from the proposed model show a good agreement with the measured strengths with a mean bias (i.e. average ratio of the measured to predicted strengths) of 1.014. The influence of ϕ and KIC on σ1 was thoroughly studied using parametric study. The study concludes that the effect of ϕ is more prominent than KIC on σ1. At a constant porosity of 0.1, the stress ratio decreases from 0.0082 to 0.0078 when KIC increases from 0.1 to 0.2, indicating a 5% decrease in stress ratio. Whereas, at a constant KIC of 0.1, the stress ratio increases from 0.0082 to 0.014 when the porosity increases from 0.1 to 0.2, indicating 71% increases in stress ratio and therefore compressive strength.

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Keywords: Compressive strength, Mode I fracture toughness, Porosity, Pore radius, Confining pressure

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Esraa M. Alomari, Kam Ng, Lokendra Khatri, 2024. Expanded pore-emanated cracking model for brittle failure of sedimentary rocks under triaxial compression. J. Rock Mech. Geotech. Eng. 16 (12), 5050-5060.

Author(s) Information

Kam Ng

✉️ kng1@uwyo.edu

Dr. Kam Ng obtained his three degrees in Civil Engineering from Iowa State University, USA. He had 10-year consulting and construction experiences. He is currently a Provost's Term Professor and Hoy Engineering Fellow at the University of Wyoming. He is a Professional Engineer registered with the state of Wyoming, USA. His research focuses on transportation and energy geotechnics and innovative construction materials. He received many awards including the 2022 Samuel Hakes Outstanding Graduate Research and Teaching Award, 2022 UW's Mid-career Graduate Faculty Mentor Award, 2013 Young Professor Paper Award from DFI, and 2012 Soil Mechanics Best Paper Award from TRB. He has published more than 70 journal papers, received more than 12 million research funding, and filed 17 patents. He has supervised two postdocs, 9 PhD and 24 MS students.