bluuebunny/crossref_metadata_2025_split huggingface dataset:
Anelastic Strain Recovery as a Measure of in Situ Stresses at FORGE
Authors: Ingraham M. D. , Ghassemi A. 
Published: August 2024

ABSTRACT:
Anelastic strain recovery, the process of measuring the time dependent recovered strain after a core is cut at depth was utilized to make a measure of the in-situ properties stresses at depth at the FORGE (Frontier Observatory for Research in Geothermal Energy) site in Milford Utah. Core was collected from a region of well 16B at approximately 4860-4870 ft. Core was instrumented with strain gages within 10 hours of the core being cut. The relaxation of the cores was measured for approximately one month, and the results analyzed, which showed that the principal stresses were slightly off vertical, and magnitudes are close to equal.

1. INTRODUCTION
Strain measurements on recovered core hold their root in the formation of the rocks themselves. As rocks are formed and stressed with burial, the grains deform and are locked in place either through cementation or through the compression of their neighbors. When cores are removed from depth the stresses are released and the strain begins to recover.
This recovered strain is measured and inverted in order to determine the principal strains, which are then converted to principal stresses though determination of the elastic modulus and application of Hooke's Law.
This technique has been applied to samples from the Utah FORGE (Frontier Observatory for Research in Geothermal Energy) site to help constrain the in-situ stress measurements at the site. The core was obtained from the 16B(78)-32 well at the site from the first core run taken above the kickoff point just below 5000 ft (core samples are from between 4865 and 4870 ft). The core is a relatively clean granitoid as shown in Fig. 1. The core was obtained on May 9th, 2023, and was instrumented within approximately 10 hours of the core being cut.

2. BACKGROUND
There are a number of ways in which in situ stresses can be determined such as hydraulic methods, i.e. fracture testing, acoustic methods, i.e. seismic waveform analysis, and core methods such as anelastic strain recovery (ASR), or overcoring.
Influence of Buttressing and Lateral Confinement on a Large Block Prior to Rockfall
Authors: Longar E. , Walton G. 
Published: August 2024

ABSTRACT:
Rockfalls are a source of danger for infrastructure near rock slopes containing potentially unstable blocks. Rockfalls can cause property damage, road blockages, and harm to people. Literature studies that monitor rock slopes have helped to demonstrate connections between rockfalls and the precursors that indicate potential instability. After identifying these precursors in potentially unstable blocks, measures can be taken to stabilize or remove the blocks to mitigate the risk to infrastructure near the slope. This study aims to evaluate the influences of buttressing effects and lateral confinement from nearby rocks on block stability through numerical modeling of a 76 m3 rockfall. Prior to the rockfall, a series of smaller rocks near the large block were displaced in association with loosening of the large block. To create the model, the topography of the block and surrounding area was digitized using photogrammetry. The rockfall process itself was simulated using the distinct element method, such that the rockmass is modeled as an assemblage of distinct blocks with boundary interactions between each block to account for the discontinuous nature of the rockmass. We used the model to evaluate trends in displacements of the block of interest with and without the presence of the surrounding smaller rocks.

1. INTRODUCTION
Rockfalls are a common hazard in mountainous areas, particularly along roadways adjacent to steep rock cuts (Copons and Vilaplana, 2008, Abellan et. al., 2010). Efforts have been put into place to monitor dangerous rock slopes, including by using LiDAR and photogrammetry to track slope change over time (Abellan et. al., 2013; Kromer et. al., 2015; Lim et al., 2005). Photogrammetry has been used as a tool to detect rockfall activity in both natural slopes (Graber and Santi, 2023) and cut slopes (Walton et. al., 2023).
One possible end-use of such monitoring data is for forecasting of future rock falls that can be mitigated before they occur. However, forecasting of rockfall events is only possible if rockfall precursors are understood (Kromer et. al., 2018, Royan et. al., 2015).
One potential precursor is the occurrence of small rockfalls before a larger failure. Monitoring of precursory rockfalls has been studied as a potential method of spatial and temporal prediction of rockfalls (Rosser et. al., 2007, Royan et. al., 2015).
Numerical Analysis of Induced Mechanism of Rockbursts in Tunnels
Authors: Deng J. , Gong Y. , Li S. 
Published: August 2024

ABSTRACT:
Rockburst is a sudden and violent failure characterized by the breaking up and expulsion of rock from its surroundings. Tunnel rockbursts pose a significant threat to the safety of excavation operations, leading to property damage and tunneler casualties. Buckling has been identified as one of the primary mechanisms causing rockbursts. Furthermore, it has been observed that rockburst can be induced by a seismic event or ambient blasting when stress waves reach the free surface of the underground opening. This paper aims to study numerically the induced mechanism of tunnel rockbursts based on the dynamic buckling of rectangular thin plates. When a rock stress wave travels toward a tunnel sidewall, it decomposes into horizontal and vertical components. The horizontal stress propagates to and reflects from the free surface, creating a rectangular thin plate of rock on the surface. The vertical stress activates parametric resonance in the rectangular thin plate, leading to the induction of a tunnel rockburst. An example of tunnel sidewall rockbursts from the Jinping II project is presented to parametrically study the effect of stress wave amplitude and frequency, static and dynamic components. Based on the mechanism analysis, measures are proposed to alleviate the hazard of tunnel rockbursts.

1. INTRODUCTION
Horizontal extended underground structures can be categorized based on the purpose of the completed structure into two types: (i) Tunnels: Extended, flat, or only slightly sloping underground cavities with excavated cross-sections exceeding 20 m2. Primarily designed for road or rail transport, each tunnel features two openings to the surface. However, in some hydropower projects such as Jinping I and II in China, there are tunnels that have only one opening to the surface due to harsh conditions. (ii) Adits, drifts, or galleries: Extended underground cavities, either horizontal or sloping at angles less than 25° to the horizontal, with relatively small diameters. These structures accommodate pipes or cables, provide access, and serve as auxiliary structures during the construction phase or for permanent use. Often, they have only one opening to the surface (Maidl et al, 2013). The present paper is concerned with rockbursts in either tunnels, adits, drifts, or galleries.
A 3D Continuum-Based Voronoi Tessellated Model (VTM) for Hard Rocks
Authors: Hamediazad F. , Bahrani N. , Moallemi S. , Yacoub T. 
Published: August 2024

ABSTRACT:
In conventional continuum numerical models, rock is typically simulated as a homogeneous material. However, these models fail to capture pre-peak tensile damage in hard rocks under compressive loading. The Discrete Fracture Network (DFN) is widely used to generate various types of rock heterogeneities at different scales. Among these, the Voronoi structure has been successfully implemented in discontinuum models to replicate the failure process of hard rocks. More recently this method has been effectively applied in 2D continuum models; however, its suitability for simulating hard rock failure in 3D continuum models has not been investigated. This paper aims to address this research gap by presenting the development of the first 3D Voronoi Tessellated Model (VTM) using the finite element program, RS3. The central objective of this study was to replicate the failure process of hard brittle rocks under unconfined compression. For this purpose, the micro-properties of a previously calibrated VTM constructed using the 2D finite element program RS2 were utilized in the RS3-VTM. The results indicate that the stress-strain curve and the peak strength of the RS3-VTM are comparable to those of the RS2-VTM. Furthermore, the simulation results demonstrate that the RS3-VTM captures the anticipated failure mode of hard rocks in laboratory unconfined compression tests.

1. INTRODUCTION
Experimental and numerical studies have indicated that, at low confinement, the failure process of brittle rocks involves the generation of localized tensile stresses due to grain-scale heterogeneities. These induced tensile stresses can lead to the initiation and propagation of tensile cracks before reaching peak stress, even when the rock medium is under an overall compressive stress field. To realistically simulate this process using numerical modeling, an explicit representation of the grain-like structure of rocks is required. Discrete Fracture Network (DFN) models are commonly used to generate various types of geological structures at different scales. Among them, the Voronoi structure has been extensively employed to replicate grain-scale heterogeneities (i.e., grains and grain boundaries) in brittle rocks.
Tackling Data-Limited Rock Mechanics Models
Authors: Maleki H. 
Published: August 2024

ABSTRACT:
Rock mechanics models are "data-limited," i.e., one seldom knows enough about a rock mass to use computational models unambiguously. Statistical methods, however, are capable of being applied where there are good data but a limited understanding of certain natural phenomena, such as the creep of rock salt or coal burst mechanics. To demonstrate the use of statistical-analytical techniques in rock mechanics problems, two case studies are used. The first study involves a historic examination of a nuclear waste repository in rock salt, where mathematical models are built using excavation convergence data to identify significant variables and estimate future deformation and stability. The second case study focuses on ongoing analysis of coal burst mechanics and associated factors. Over the last three decades, a hybrid statistical-analytical methodology has been applied for identifying significant factors affecting coal burst. The final model utilizes data from 30 case studies from Utah, Colorado, Kentucky, and other Eastern U.S. mines providing predictive capability for the entire United States coal fields.

1. INTRODUCTION
There are two methods used by engineers and researchers as tools to help predict conditions in the future: statistical and computational. Starfield and Cundall (1988) identify rock mechanics models as "data-limited," that is, one seldom knows enough about a rock mass to use computational models unambiguously. Statistical methods, on the other hand, are uniquely capable of being applied where there are good data but a limited understanding of certain natural phenomena, such as the creep of rock salt or elevated risk domains associated with the violent failure of strata commonly referred to as coal bumps or bursts. Rock bursts and coal bumps are defined as sudden, violent failure that occur near mine entries that are of such a magnitude that they expel large amount of rock and/or coal into an excavation, restricting safe and efficient access to the working area (Maleki and White 1997). Gradual failure and spalling is common in coal mine environment and is considered not problematic but controlled through proper mine orientation and application of support as needed. Important to these real-world statistical evaluations are (1) having sufficient number of data collected consistently and (2) incorporation of analytical calculations for quantifying geologic, mining and particularly geotechnical variables. By combining the strength of the statistical and analytical models, an improved "hybrid" model is created and utilized. Powerful examples of the use of statistical techniques to evaluate stability and performance using significant field investigations are given by Parson and Dahl (1971), Maleki and White (1997), Maleki and Owen (2001), Maleki et al. (2001), Maleki et al. (2023), and Maleki (2023).
Tool Development and Field Test of the Stress Measurement Method with Dual Bit Coring Applicable to Geothermal Fields
Authors: Ito T. , Kaneko K. , Sasaki M. , Ogawa K. , Yokoyama T. , Funato A. , Tezuka K. 
Published: August 2024

ABSTRACT:
The Dual Bit Coring (DBC) is the method to record the in-situ stress state into cross-sectional shapes of a boring core. The magnitudes and orientations of the in-situ stresses in a plane perpendicular to the borehole can be estimated from the measured core diameters upon the principle with which the core expand radially in an elastic manner as it is relieved from the in-situ stresses. We developed a downhole assembly to realize DBC which contains small and large diameter bits. A core sample is cut out in three stages with changing those two bits. We developed another downhole tool to detect the core orientation. They are designed to operate in temperatures more than 200 °C at depths of a few km considering application to geothermal fields. We simulated the three-stage coring by numerical simulations and confirmed the core to have cross sections of an expanded-elliptical shape and a circular shape prior to expansion in the lower and middle sections, respectively. We tested the tools in field tests and estimated the in-situ stress state successfully.

1. INTRODUCTION
Rock core samples obtained by drilling have slightly elliptical cross-sections instead of circular ones, when the in-situ stress state is anisotropic (Funato and Ito, 2017). Such elliptical shapes arise as the core expand radially in an elastic manner when it is relieved from the in-situ stress. The amount of expansion is proportional to the stress magnitude. The core expands most and least in the orientations of the maximum and minimum stresses, respectively, that act along the plane that is perpendicular to the drill hole, resulting in the elliptical cross-section.
We applied the phenomenon of core expansion to measure the in-situ stress state. To do this, we proposed a novel coring method referred to as Dual Bit Coring (DBC) that results in a single core that has two signature transverse cross-sections: the first has an elliptical shape resulting from core expansion and the second records the initial circular shape prior to expansion. Then the amount of expansion can be estimated as the difference between the cross-sections prior and posterior to expansion, and the stress magnitudes and orientations can be estimated from the circumferential distribution of the core expansion.
Impact of Cold Fluid Injection on Hydraulic Fracture Propagation
Authors: Rueda J. , Mejía C. , Firme P. , Roehl D. , Rossi D. , Henriques F. , Sousa E. , Chaves R. 
Published: August 2024

ABSTRACT:
Hydraulic fracturing is widely employed to enhance permeability and well-reservoir connectivity, increasing fluid flow and heat transfer in oil/gas/geothermal reservoirs. Analytical and numerical solutions have been developed for predicting the hydraulic fracture propagation. However, most solutions neglect the thermal effects within the porous medium and in the fracture development, even though these effects strongly affect the properties of the rock formation and the injected fluid. This work studies the effects of cold fluid injection on induced hydraulic fracture propagation. To this end, a fully coupled thermo-hydro-mechanical (THM) finite element model was adopted. The model simulated fracture propagation using interface elements with a thermo-pore-cohesive zone model (TPCZM). The presented model is verified against related analytical and numerical solutions. Moreover, the work investigates the influence of cold fluid injection under leak-off-dominated regimes. The numerical results show that injection period, heat transfer, and initial stresses significantly impact the fluid leak-off, pore pressure evolution and fracture geometry growth. Finally, the study adds valuable insight to a better understanding of the complex hydraulic fracturing process considering thermal, hydraulic, and mechanical coupled behaviors.

1. INTRODUCTION
The hydraulic fracturing technique is widely employed to enhance permeability and well-reservoir connectivity, increasing fluid flow and heat transfer in oil/gas/geothermal reservoirs (Barbier, 2002; O'Sullivan et al., 2001). Other applications include rock-burst control and cave inducement in deep mining (Board et al., 1992; Jeffrey & Mills, 2000; Van As & Jeffrey, 2000), waste disposal in shale (de Laguna, 1966; Maloney & Yoxtheimer, 2012), and assessment of in situ stresses (Desroches, 1995). Modeling efforts on hydraulic fracturing have attracted numerous research contributions in the last decades (Green & Sneddon, 1950; Khristianovic & Zheltov, 1955; Nordgren, 1972; Perkins & Kern, 1961; Sneddon, 1946). Simplified analytical solutions based on KGD, PKN, or penny-shaped geometries have been presented to predict fluid pressure evolution, opening, size, and profile of the fracture (Adachi & Detournay, 2002, 2008; Bunger et al., 2005; Detournay, 2016; Dontsov, 2016, 2017; Garagash et al., 2011; Savitski & Detournay, 2002). These models are excellent approaches for studying hydraulic fracture evolution in different regimes of propagation (Adachi & Detournay, 2008; Rueda Cordero et al., 2020). However, analytical solutions consider a basic description of rock properties and infinite elastic homogenous media (Adachi & Detournay, 2008). Furthermore, these solutions neglect the thermo-hydro-mechanical (THM) effects within the permeable porous medium.
Geomechanics Finite Element Modelling for Nuclear Waste Storage
Authors: Mohamad-Hussein A. , Ni Q. , Haas M. , De Gennaro V. , Subbiah S. K. , Rodriguez-Herrera A. 
Published: August 2024

ABSTRACT:
Nuclear energy represents one of the key energy sources that will make it possible to achieve net-zero carbon emissions. Safe and efficient management are crucial requirements when dealing with radioactive waste. Once a geological repository is selected, the development of site involves various stages. Site characterisation represents one of the early phases. It includes performing geological, hydrogeological, and other studies to understand the site's suitability for nuclear waste storage. This paper is devoted to modelling the radioactive waste disposal into a geological repository. A comprehensive geomechanics finite element modelling approach is adopted to address the challenges arising from nuclear waste storage.
A unified finite element model has been constructed for the shaft, gallery, and storage cavities. Finite element modelling has been performed to simulate the excavation of the various underground structures within the host rock formation. Hydromechanical simulations were conducted for excavating the various cavities. The installation of the radioactive waste containers is simulated. The behaviour is investigated by simulating the impact of thermal heating on the surrounding formations.
This work serves as a critical step towards achieving the safe containment isolation of radioactive materials and reducing environmental risk as we move towards a future powered by clean, sustainable energy sources and commitment to net-zero emissions.

1. INTRODUCTION
As one of the least greenhouse gas emitting energy sources, nuclear energy has been shown to be essential for delivering low-carbon sustainable energy transitions (Gibb 1999). However, it is also widely acknowledged that safe disposal of spent nuclear fuel (nuclear waste) can present significant social, environmental, and technical challenges (Themann and Brunnengräber 2021; Christiansson 2014). The concept of nuclear waste storage is to isolate radioactive material from humans and the environment for sufficiently long time periods. Therefore, storing such waste in deep impermeable geological formations is considered a viable option (McKinley et al. 2007). Regardless of the choice of rock type, the general design of the storage solution requires placing the nuclear waste container in a chamber created in a geological formation. However, high-level radioactive waste with associated heating and cooling processes over long period of time causes complex changes to the surrounding rocks. Their nature and performance can change according to the internal and external conditions and ultimately could affect the integrity of the storage chamber (Jia et al. 2006; Teng et al. 2021; Plúa et al. 2021). To achieve the engineering safety of the storage chamber, it is necessary to carefully investigate and manage the risks associated.
Mode I Fracture Behavior of Lightweight Concrete Made of Mine-Tailings-Based Aggregates
Authors: Asadizadeh M. , Hedayat A. , Tunstall L. , Taboada Neira M. , Vega González J. A. , Verá Alvarado J. W. 
Published: August 2024

ABSTRACT:
The exploration of mode I fracture behavior in lightweight concrete (LW-concrete) made from mine-tailings-based aggregates holds great significance in the realm of construction materials. This research is vital, as it offers crucial insights into the structural integrity of the material and its suitability for diverse applications. The utilization of mine tailings (MTs), abundant in aluminum oxide and silicon dioxide, and their transformation into lightweight aggregates (LWAs) signifies an environmentally responsible approach to address the environmental impact of MTs while reducing disposal costs. This study explored the fracture behavior of LW-concrete composed of mine-tailings-based aggregates, particularly under mode I loading. This aspect necessitates a comprehensive examination of this innovative material. Mode I fracture tests were performed on three-point bending beam specimens to better understand the fracture behavior. Using alkali-activation and palletization techniques, LWAs were produced using a blend of 30 wt.% fly ash type F and 70 wt.% MTs. The concrete mix incorporated a combination of coarse LWAs and natural, normal-weight fine aggregates. Specialized molds were employed for the direct casting of notched beam specimens, which were subsequently subjected to three-point bending tests after the curing process. The study revealed a mode I fracture toughness of 434.88 kNm^1/2, a crack tip opening displacement (CTOD) of 90.28 μm, and the characteristics of the fracture process zone (FPZ) measuring 2.88 mm, with comprehensive analysis conducted using Digital Image Correlation (DIC).

1. INTRODUCTION
Natural aggregates find widespread applications in civil engineering and construction industry. They hold significant importance in the manufacturing of concrete (Guo et al., 2020), building roads (Ryms et al., 2015), surfacing asphalt (Qian et al., 2013), and other related applications. However, since natural resources are scarce and their utilization may have adverse environmental effects (Tabsh & Abdelfatah, 2009), there is an increasing interest in manufacturing lightweight aggregates (LWAs) utilizing waste materials like mine tailings (MTs) (M. Asadizadeh et al., 2023b, 2023a; Mostafa Asadizadeh et al., 2023, 2024; Yliniemi et al., 2017).