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1. Modeling of rock inhomogeneity and anisotropy by explicit and implicit representation of microcracks

   Abedi, Reza; Clarke, Philip L. (January 2018, Proceedings of ARMA 2018)

   Fracture in rock as a heterogeneous brittle material, having significant inherent randomness, requires including probabilistic considerations at different scales. Crack growth in rocks is generally associated with complex features such as crack path oscillations, microcrack and crack branching events. Two methods will be presented to address rock inhomogeneity and anisotropy. First, microcracks are explicitly realized in a domain based on specific statistics of crack length and location. Second, a statistical model is used to implicitly represent an inhomogeneous field for fracture strength. Both approaches can be used for rocks in which the natural fractures are oriented in a specific angle, i.e. an aspect for modeling bedding planes in sedimentary rocks. 

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2. Influence of clay-doped water on permeability in granite rock mass

   Yoshitaka NARA, Koki KASHIWAYA (December 2023, Journal of the Society of Materials Science, Japan)

   抄録 It is important to understand the long-term migration of radionuclides when considering long-lasting rock engineering projects such as the geological disposal of radioactive waste. The network of fractures and pores in a rock mass plays a major role in fluid migration as it provides pathways for fluid flow. The geometry of such a network can change due to fracture sealing by fine-grained material over extended periods of time. Groundwater commonly contains fine-grained material such as clay minerals, and it is probable that such minerals accumulate within rock fractures during groundwater flow, thereby decreasing fracture apertures and bulk permeability. It is therefore essential to conduct permeability measurements using water that includes fine-grained minerals in order to understand the evolving permeability characteristics of rock. However, this has not been studied to date in in-situ rock mass. Therefore, in the present study, we perform permeability measurements in a granite rock mass to investigate the change of permeability that occurs under the flow of water that includes clays. Our findings show that clay particles accumulate in fractures and that the permeability (hydraulic conductivity) of the granite rock mass decreases over time. The decrease was more significant in the earlier time. We conclude that the accumulation of clay minerals in the fracture decreases the permeability of a rock mass. Furthermore, we consider that the filling and closure of fractures in rock is possible under the flow of groundwater that contains clay minerals. 

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3. Identifying fracture-controlled resonance modes for structural health monitoring: insights from Hunter Canyon Arch (Utah, USA)

   https://doi.org/10.5194/esurf-13-81-2025  

   Grechi, Guglielmo; Moore, Jeffrey R; McCreary, Molly E; Jensen, Erin K; Martino, Salvatore (January 2025, Earth Surface Dynamics)

   Abstract. Progressive fracturing contributes to structural degradation of natural rock arches and other freestanding rock landforms. However, methods to detect structural changes arising from fracturing are limited, particularly at sites with difficult access and high cultural value, where non-invasive approaches are essential. This study aims to determine how fractures affect the dynamic properties of rock arches, focusing on resonance modes as indicators of structural health conditions. We hypothesize that damage resulting from fracture propagation may influence specific resonance modes that can be identified through ambient vibration modal analysis. We characterized the dynamic properties (i.e., resonance frequencies, damping ratios, and mode shapes) of Hunter Canyon Arch, Utah (USA), using spectral and cross-correlation analyses of data generated from an array of nodal geophones. Results revealed properties of nine resonance modes with frequencies between 1 and 12 Hz. Experimental data were then compared to numerical models with homogeneous and heterogeneous compositions, the latter implementing weak mechanical zones in areas of mapped fractures. All numerical solutions replicated the first two resonance modes of the arch, indicating these modes are insensitive to structural complexity derived from fractures. Meanwhile, heterogenous models with discrete fracture zones succeeded in matching the frequency and shape of one additional higher mode, indicating this mode is sensitive to the presence of fractures and thus most likely to respond to structural change from fracture propagation. An evolutionary crack damage model was then applied to simulate fracture propagation, confirming that only this higher mode is sensitive to structural damage resulting from fracture growth. While examination of fundamental modes is common practice in structural health monitoring studies, our results suggest that analysis of higher-order resonance modes can be more informative for characterizing fracture-driven structural damage. 

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4. Progressive fracturing in alluvial clasts

   https://doi.org/10.1130/B36670.1  

   Shaanan, Uri; Mushkin, Amit; Rasmussen, Monica; Sagy, Amir; Meredith, Philip; Nara, Yoshitaka; Keanini, Russell; Eppes, Martha-Cary (July 2023, Geological Society of America Bulletin)

   Rock fracturing sets the pace for a range of geomorphic processes. While experimental studies and modeling have provided invaluable insights into the mechanisms and rates of rock fracturing as a function of stress, time, and environmental conditions, field-based observations of subaerial fracturing evolution over geologic time are scarce. To address this knowledge gap, we conducted a systematic study of fractures that developed subaerially and in situ within clasts perched on abandoned late Quaternary alluvial surfaces (ca. 0, ca. 14, and ca. 62 ka in age) in the hyperarid Dead Sea Rift Valley, Israel. Using quantitative field observations, petrographic, and scanning electron microscopy, and micron-scale laser scans of fracture surfaces we found that fractures exhibit a consistent pattern of three distinctive weathering zones: (1) an “Outer Zone,” where fracture surface morphology resembles the clast exterior; (2) an “Accumulation Zone,” where fractures are infilled by “loose” accumulated particles; and (3) an “Inner Zone” where fractures extend inward to the crack-tip and preferentially follow grain boundaries. Crack-tips are characterized as a distinct micro domain that consists of fracture-parallel microcracks, chemical alteration, and dissolution morphologies. Altogether, the laboratory results indicate chemically enhanced fracturing and infiltration of water ahead of traction-free, open crack-tips. Field measurements also revealed an increase in fracture number density over geologic time. Our results highlight new details regarding the progressive nature of mechanical weathering through geologic time and the role of moisture as a potential rate-setting factor in the fracturing that allows mechanical weathering. 

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5. Radar imaging of fractures and voids behind the walls of an underground mine

   https://doi.org/10.1190/geo2020-0763.1  

   Abbasi Baghbadorani, Amin; Hole, John A.; Baggett, Jonathan; Ripepi, Nino (July 2021, GEOPHYSICS)

   Two- and three-dimensional rock-penetrating-radar data were acquired on the wall of a pillar in an underground limestone mine. The objective was to test the ability of radar to image fractures and karst voids and to characterize their geometry, aperture, and fluid content, with the goal of mitigating mining hazards. Strong radar reflections in the field data correlate with fractures and a cave exposed on the pillar walls. Large pillar wall topography was included in the steep-dip Kirchhoff migration algorithm because standard elevation corrections are inaccurate. The depth-migrated 250 MHz radar images illuminate fractures, karst voids, and the far wall of the pillar up to approximately 25 m depth into the rock, with a spatial resolution of <0.5 m. Higher frequency radar improved the image resolution and aided in the interpretation, but at the cost of shallower depth of penetration and extra acquisition effort. Due to the strong contrast in physical properties between the rock and the fracture fluid, fractures with apertures as thin as a 50th of a radar wavelength were imaged. Water-filled fractures with mm-scale aperture and air-filled fractures with cm-scale apertures produce strong reflections at 250 MHz. A strong variation in the reflection amplitude along each fracture is interpreted to represent the variable fracture aperture and the nonplanar fracture structure. Fracture apertures were quantitatively measured, but distinguishing water from air-filled fractures was not possible due to the complex radar wavelet and fracture geometry. Two conjugate fracture sets were imaged. One of these fracture sets dominates the rock mass stability and water inrush challenges throughout the mine. All of the detected voids and a large cave are at the intersection of two fractures, indicating preferential water flow and dissolution along conjugate fracture intersections. Detecting, locating, and characterizing fractures and voids prior to excavation can enable miners to mitigate potential collapse and flood hazards before they occur. 

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