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Geosciences
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Fracture Geomechanics—Obstacles and New Perspectives
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Fracture Geomechanics—Obstacles and New Perspectives

A special issue of Geosciences (ISSN 2076-3263). This special issue belongs to the section "Geomechanics".

Deadline for manuscript submissions: closed (15 March 2025) | Viewed by 6692

Special Issue Editors

Dr. Wenfeng Li

E-Mail Website
Guest Editor
Earth and Environmental Sciences, Los Alamos National Laboratory, Los Alamos, NM 87545, USA
Interests: geomechanics; flow in porous media; thermo-hydro-mechanical–chemical coupling
Dr. Shahrzad Roshankhah

E-Mail Website
Guest Editor
Civil and Environmental Engineering, The University of Utah, Salt Lake City, UT, 84112, USA
Interests: renewable energy systems; thermo-hydro-mechanical–chemical coupling; porous media; acoustic emission; neutron imaging; experimental and computational geomechanics

Special Issue Information

Dear Colleagues,

The objective of this Special Issue of Geosciences is to disseminate and discuss recent advances in the geomechanics of subsurface fractures by collecting high-quality original research articles, reviews, and technical notes.

The geomechanics of fractures finds applications in many subsurface engineering disciplines at the forefront of sustainable fossil-energy extraction and green-energy transition. This is because fractures strongly impact fluid flow, solute transport, seismicity, and rock mass failure in the subsurface. Hence, there is an increasing interest in the sophisticated characterization, modeling, prediction, and management of subsurface fractures. Nevertheless, the current understanding of fracture geomechanics is fairly limited, hindering safe and efficient operations in underground mining, hydrocarbon recovery, enhanced geothermal systems, geological CO2 sequestration/mineralization, subsurface energy (H2, Gas) storage, nuclear waste disposal, etc. To push the knowledge boundary and benefit global geo-resource utilization, we would like to invite you to submit your recent work on experimental, computational modeling, and field studies of subsurface fractures with respect to the following topics:

  • Hydraulic fracturing and interactions with natural geological discontinuities;
  • Hydro-mechanical coupling of fracture and fluid flow;
  • Hydromechanical interactions of the fracture network and rock matrix;
  • Shear fracturing and seismicity;
  • Fracture geomechanics on the structural failure of underground openings (tunnels, boreholes, caves, etc.);
  • Impact of geochemical reactions on fracture geomechanics;
  • Constitutive behavior of fracture geomechanics;
  • Fracture geomechanics in the geothermal environments;
  • Monitoring of fracture geomechanical behavior;
  • Application of machine learning and probabilistic modeling in fracture geomechanics.

Dr. Wenfeng Li
Dr. Shahrzad Roshankhah
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Geosciences is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1800 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • hydraulic fracturing
  • natural fractures
  • thermo-hydro-mechanical–chemical coupling
  • process monitoring systems
  • acoustic emission
  • seismicity
  • constitutive laws
  • machine learning
  • flow in fractured porous media
  • uncertainty quantification

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Published Papers (5 papers)

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31 pages, 5534 KiB  
Article
Safety Assessment of Concrete Gravity Dams: Hydromechanical Coupling and Fracture Propagation
by Maria Luísa Braga Farinha, Nuno Monteiro Azevedo and Sérgio Oliveira
Geosciences 2025, 15(4), 149; https://doi.org/10.3390/geosciences15040149 - 15 Apr 2025
Viewed by 188
Abstract
For the safety assessment of concrete dam–foundation systems, this study used an explicit time-stepping small-displacement algorithm, which simulates the hydromechanical interaction and considers the discrete representation of the foundation discontinuities. The proposed innovative methodology allows for the definition of more reliable safety factors [...] Read more.
For the safety assessment of concrete dam–foundation systems, this study used an explicit time-stepping small-displacement algorithm, which simulates the hydromechanical interaction and considers the discrete representation of the foundation discontinuities. The proposed innovative methodology allows for the definition of more reliable safety factors and the identification of more realistic failure modes by integrating (i) softening-based constitutive laws that are closer to the real behavior identified experimentally in concrete–concrete and concrete–rock interfaces; (ii) a water height increase that can be considered in both hydraulic and mechanical models; and (iii) fracture propagation along the dam–foundation interface. Parametric studies were conducted to assess the impact of the mechanical properties on the global safety factors of three gravity dams with different heights. The results obtained using a coupled/fracture propagation model were compared with those from the strength reduction method and the overtopping scenario not considering the hydraulic pressure increase. The results show that the safety assessment should be conducted using the proposed methodology. It is shown that the concrete–rock interface should preferably have a high value of fracture energy or, ideally, higher tensile and cohesion strengths and high associated fracture energy. The results also indicate that with a brittle concrete–rock model, the predicted safety factors are always conservative when compared with those that consider the fracture energy. Full article
(This article belongs to the Special Issue Fracture Geomechanics—Obstacles and New Perspectives)
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17 pages, 6558 KiB  
Article
Outcrop-Scale Hydraulic Fracturing Experiments with a Coagulable Resin and Data Analysis Results
by Tsutau Takeuchi, Akira Fujimoto, Ryohei Inoue, Tsuyoshi Ishida, Takashi Danjo, Tatsuya Yokoyama and Hirokazu Fujii
Geosciences 2025, 15(3), 103; https://doi.org/10.3390/geosciences15030103 - 14 Mar 2025
Viewed by 415
Abstract
Hydraulic fracturing is a crucial technology for resource development, such as shale gas, and its optimization is necessary to enhance development efficiency. However, evaluating fracture shapes involves technical uncertainties. Japan Organization for Metals and Energy Security (JOGMEC) and Kyoto University have conducted laboratory-scale [...] Read more.
Hydraulic fracturing is a crucial technology for resource development, such as shale gas, and its optimization is necessary to enhance development efficiency. However, evaluating fracture shapes involves technical uncertainties. Japan Organization for Metals and Energy Security (JOGMEC) and Kyoto University have conducted laboratory-scale hydraulic fracturing experiments using coagulable fluorescent resin as the injection fluid (resin fracturing test) to visualize hydraulic fractures and investigate their relationship with acoustic emissions (AEs) generated during fracturing. Since lab-scale experiments can only examine the phenomena near the injection hole owing to size limitations, we designed an experiment to apply the visualization method to the outcrop scale. This paper presents the results from an in situ, outcrop-scale hydraulic fracturing experiment conducted at the Kamioka Mine, Gifu Prefecture, Japan, from 2022 to 2023, with goals similar to those of the laboratory experiments. A resin fracturing borehole (RF1) with a diameter of 76 mm was core-drilled to a depth of approximately 10 m for the resin fracturing tests. AEs were observed in five boreholes drilled around RF1 at the same depth. Resin fracturing tests were performed at two different depths, with breakdown confirmed at both. A core of a larger diameter (205 mm) was recovered by coaxial overcoring around RF1, and resin-filled fractures were observed under black light on the core surfaces. After the resin fracturing experiment, two analyses were performed using the acquired core and AE data to predict the fracture extension and the mechanism of AE occurrence. We compared the distribution of AE events and visualized fractures in the core. Additionally, we compared the stress direction estimated from failure mechanism analysis using AE data with the maximum stress direction estimated from hydraulic fracturing. Our analysis provided several insights into fracture extension. The distribution of AE hypocenters was consistent with the direction of the hydraulic fractures confirmed by coring after the resin fracturing test. The failure mechanisms are classified based on the polarity of the first P-wave motion of the AE waveform. However, the actual scale of oil fields is significantly larger than that considered in this study. Discussing visible fractures created by hydraulic fracturing is deemed meaningful. We expect that the results of this study will provide valuable information for the precise estimation of hydraulic fractures. Full article
(This article belongs to the Special Issue Fracture Geomechanics—Obstacles and New Perspectives)
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25 pages, 11268 KiB  
Article
Optimized Random Forest Models for Rock Mass Classification in Tunnel Construction
by Bo Yang, Danial Jahed Armaghani, Hadi Fattahi, Mohammad Afrazi, Mohammadreza Koopialipoor, Panagiotis G. Asteris and Manoj Khandelwal
Geosciences 2025, 15(2), 47; https://doi.org/10.3390/geosciences15020047 - 2 Feb 2025
Cited by 2 | Viewed by 957
Abstract
The accurate prediction of rock mass quality ahead of the tunnel face is crucial for optimizing tunnel construction strategies, enhancing safety, and reducing geological risks. This study developed three hybrid models using random forest (RF) optimized by moth-flame optimization (MFO), gray wolf optimizer [...] Read more.
The accurate prediction of rock mass quality ahead of the tunnel face is crucial for optimizing tunnel construction strategies, enhancing safety, and reducing geological risks. This study developed three hybrid models using random forest (RF) optimized by moth-flame optimization (MFO), gray wolf optimizer (GWO), and Bayesian optimization (BO) algorithms to classify the surrounding rock in real time during tunnel boring machine (TBM) operations. A dataset with 544 TBM tunneling samples included key parameters such as thrust force per cutter (TFC), revolutions per minute (RPM), penetration rate (PR), advance rate (AR), penetration per revolution (PRev), and field penetration index (FPI), with rock classification based on the Rock Mass Rating (RMR) method. To address the class imbalance, the Borderline Synthetic Minority Over-Sampling Technique was applied. Performance assessments revealed the MFO-RF model’s superior performance, with training and testing accuracies of 0.992 and 0.927, respectively, and key predictors identified as PR, AR, and RPM. Additional validation using 91 data sets confirmed the reliability of the MFO-RF model on unseen data, achieving an accuracy of 0.879. A graphical user interface was also developed, enabling field engineers and technicians to make instant and reliable rock classification predictions, greatly supporting safe tunnel construction and operational efficiency. These models contribute valuable tools for real-time, data-driven decision-making in tunneling projects. Full article
(This article belongs to the Special Issue Fracture Geomechanics—Obstacles and New Perspectives)
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33 pages, 6962 KiB  
Article
Experimental Study: Stress Path Coefficient in Unconsolidated Sands: Effects of Re-Pressurization and Depletion Hysteresis
by Sabyasachi Prakash, Michael Myers, George Wong, Lori Hathon and Duane Mikulencak
Geosciences 2024, 14(12), 327; https://doi.org/10.3390/geosciences14120327 - 3 Dec 2024
Viewed by 1060
Abstract
Accurate estimation of in-situ stresses is a critical parameter for geo-mechanical modelling. In-situ stresses are estimated in the field from logs and frac tests. Laboratory tests are performed with cored material to estimate horizontal stress changes under defined boundary conditions to complement field [...] Read more.
Accurate estimation of in-situ stresses is a critical parameter for geo-mechanical modelling. In-situ stresses are estimated in the field from logs and frac tests. Laboratory tests are performed with cored material to estimate horizontal stress changes under defined boundary conditions to complement field data. Horizontal stress path coefficient is used to estimate a change in in-situ stresses as the reservoir undergoes depletion or injection. Uniaxial Strain boundary conditions are representative of far field stress state. The laboratory data provides the change in horizontal stress with a change in pore pressure. It is used to complement the field data acquisition of absolute stress values to predict the value of total stresses. This experimental study provides a novel method of simulating geological compaction for fabricating representative samples from unconsolidated sands. It investigates the variability of horizontal stress path coefficient as a function of changing pore pressure (depressurization and re-pressurization) in unconsolidated sandstone reservoirs. Synthetic sandstones samples were made from sand packs by consolidating them under an isostatic stress path at ambient pore pressure. After getting to initial reservoir conditions, a series of pore pressure depletion and injection tests with varying magnitudes (injection and depletion) were performed to study the effects of stress path direction and associated hysteresis. The magnitude of the stress path coefficient under depletion is lower than that under injection for the first load-unload cycle. In subsequent load-unload cycles, the stress path coefficient values remain constant until the sample is depleted to a new level of pore pressure. A Modified Cam Clay model is fit to the data to map the expansion of the yield surface and quantify the model parameters. Application of this research includes accurate prediction of changes in-situ stresses during depletion and injection stress paths for simulating unconsolidated reservoirs behavior under fluid injection or further depletion. Full article
(This article belongs to the Special Issue Fracture Geomechanics—Obstacles and New Perspectives)
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16 pages, 4074 KiB  
Technical Note
Laboratory Hydraulic Tensile Strength Correlation with Strength-Based Brittleness Indices for Carbonate Reservoirs
by Mohammad Ezazi, Ebrahim Ghorbani, Ali Shafiei, Ebrahim Sharifi Teshnizi and Brendan C. O’Kelly
Geosciences 2024, 14(2), 52; https://doi.org/10.3390/geosciences14020052 - 15 Feb 2024
Cited by 2 | Viewed by 2134
Abstract
Hydraulic fracturing (HF) is the primary choice for stimulating petroleum reservoirs. Rock tensile strength and brittleness are crucial parameters required for screening candidate reservoirs and in designing successful HF operations. However, in situ and laboratory determinations of the hydraulic tensile strength (HTS) of [...] Read more.
Hydraulic fracturing (HF) is the primary choice for stimulating petroleum reservoirs. Rock tensile strength and brittleness are crucial parameters required for screening candidate reservoirs and in designing successful HF operations. However, in situ and laboratory determinations of the hydraulic tensile strength (HTS) of rock can prove problematic. Alternatively, the HTS could be estimated from the rock brittleness once a reliable relationship has been established between them. Accordingly, this paper investigates the correlations between the HTS, as measured using laboratory hydraulic fracture tests, and ten strength-based brittleness indices (BIs) selected from the research literature. The primary inputs for computing these BIs are uniaxial compressive strength (UCS) and the Brazilian tensile strength (BTS), which are typically measured for most projects using standard laboratory rock mechanics tests or obtained from log data. For the purposes of this experimental investigation, intact rock core samples were obtained from a carbonate–dolomite formation in Iran, comprising eight distinct geomechanical units, with measured values of UCS, BTS, and HTS ranging 29.7–162.2, 1.93–12.23, and 7.20–20.63 MPa, respectively. The measured HTS was found to directly correlate with the UCS, BTS, and Young’s modulus, and inversely correlated with the rock porosity. Seven of the ten investigated BIs correlated with the measured HTS over 69% (R2 ≥ 0.69). In particular, the BI expressions developed by Yagiz and Gokceoglu, Ghadernejad et al., and Khandelwal et al. exhibited relatively strong correlations with the measured HTS (producing R2 values of 0.94, 0.87, and 0.86, respectively), suggesting that these three HTS–BI correlations could be used to provide preliminary HTS estimates for the investigated carbonate–dolomite formation in Iran. This work adds to a database that can be expanded to include other geographical regions for providing useful information about the selection of a suitable site or reserve for conducting HF operations. Full article
(This article belongs to the Special Issue Fracture Geomechanics—Obstacles and New Perspectives)
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