bluuebunny/crossref_metadata_2025_split huggingface dataset:
Groundwater Drainage-Induced Rock Mass Deformation During the Gotthard Base Tunnel Excavation in the Swiss Alps: 3D Modelling and Comparison to Field Measurements
Authors: Zhao C. , Lei Q. , Zhang Z. , Loew S. 
Published: September 2022

ABSTRACT:
The Gotthard Base Tunnel (GBT), constructed between 2000 and 2011, is a 57 km long and up to 2.5 km deep high-speed railway tunnel located in the Swiss Alps. Significant ground surface displacements up to 10 cm were observed during and after the tunnel construction. To gain a better understanding of the physical mechanisms underpinning such conspicuous ground deformations, we develop a 3D fully-coupled hydro-mechanical model to simulate the excavation-induced groundwater drainage, stress perturbation, and poroelastic response in faulted rock masses over both space and time. First, we construct a geological model with topographical features, lithological units, and natural faults realistically represented. We constrain the material properties of faults and rock masses based on extensive laboratory testing results and site characterisation datasets. We then simulate the tunnelling process with the resulting coupled hydro-mechanical responses of the faulted rock captured and ground surface displacements analysed. The simulation results show a good agreement with the field monitoring data of both ground surface displacement and tunnel settlement. The research findings from our work have important implications for many groundwater drainage-related geoengineering activities such as underground excavation in alpine mountains and fluid withdrawal in subsurface reservoirs.

1 INTRODUCTION
The Gotthard Base Tunnel (GBT) is a 57 km long and up to 2.5 km deep high-speed railway tunnel located in the Central Alps of Switzerland (Fig. 1). The excavation work of the two tunnel tubes started in 2000 and successfully completed in 2011. The Sedrun and Faido sections of the GBT are located in crystalline basement rocks of the Gotthard Massif, where three arch dams are located on the ground surface at the Nalps, Curnera and St. Maria hydropower lakes. Due to the significant concern regarding the safety of these nearby hydropower infrastructures during and after the GBT excavation, a comprehensive in-situ monitoring system was installed to closely monitor the surface displacement and tunnel inflow/settlement. According to the monitoring data, up to 10 cm surface displacements and 50L/s tunnel inflow took place during the construction period (Loew et al., 2015).
Critical Crack Opening of Charcoal Granite
Authors: Fakhimi A. , Asem P. , Tarokh A. , Labuz J. F. 
Published: September 2022

ABSTRACT:
A simple testing apparatus has been designed for measurement of tensile strength of rock and characterization of fracture parameters such as critical crack opening displacement. The apparatus is a hardened-steel beam with a notch and a cut-out, designed so that the rock specimen is subjected to uniform stress through its thickness with negligible bending. The dimensions of the apparatus are length = 280.0 mm, height = 100.0 mm, and thickness = 26.5 mm; the notch length = 60.0 mm and width = 2.0 mm. Two strain gages, SG 1 and 2, are attached near the notch tip and the apparatus is calibrated to provide the tensile stress in the specimen. A Charcoal granite specimen with side notches at its center was used for testing within a closed-loop, servo-hydraulic load with crack opening displacement (COD) at a rate of 0.02 micron/s used as the feedback signal. The rock specimen was attached to the bottom cut-out using an epoxy adhesive. Two strain gages were installed on the rock surface close to the notch tips. Digital image correlation (DIC) was used to investigate the displacement field and the symmetry of displacement along the ligament length. The crack initiation and propagation in the post-peak regime is discussed using the data from the strain gages and DIC. The results show that the apparatus can be used to investigate post-peak response and critical crack opening displacement of a brittle rock.

1. INTRODUCTION
The cohesive crack model (Dugdale 1960; Barenblatt 1962;) and its extension (Hillerborg et al. 1976) have been widely used to describe the process of fracture in geomaterials. Hillerborg et al. (1976) assumed that in a direct tensile test, the strains are uniformly distributed along the specimen width until the peak stress is achieved. At the peak, a cohesive crack develops that is assumed to transfer tensile stresses. As the crack opening increases, the specimen softens.
Microphysics-Informed Tension/Compression Asymmetry of Damage Evolution in Granular Materials
Authors: Bryant E. C. , Miller N. A. , Bennett K. C. 
Published: September 2022

ABSTRACT:
Granular micromechanics and micro-plane models have been widely used to numerically approximate failure modes of geomaterials since the latter was proposed by Zienkiewicz and Pande in the 1970s for fractured rocks and soils. These closely-related numerical models develop continuum formulations that can capture a broad range of the complex material behavior that granular materials and rocks exhibit during induced damage and plastic deformations, which is formulated mathematically by aggregating the mesoscale mechanical response due to microscale failure events like slip along rock planes. In this work, we give an overview of a general approach to derive continuum damage-viscoelastoplastic material models from microscale inter-granular contact and micro-plane models, providing the example of apex-smoothed Drucker-Prager plasticity expressing tension/compression compression asymmetry of the damage evolution. Macroscopic damage and plasticity are characterized by their microscale counterparts, e.g., the pressure-sensitivity factor for the classical Drucker-Prager yield criterion is explicitly related to the friction coefficient governing stick-slip events. A significant benefit of the proposed constitutive modeling framework over existing models is that the damage and plasticity evolve based on microscale energy arguments, rather than by heuristic attribution of observed macroscale phenomena to a particular dissipative process. Model predictions for frictional geomaterials are exercised against experimental data for geopolymer concrete under confined compaction from the literature.

1 INTRODUCTION
Unlike brittle materials like pure concretes and hard rock, a large class of cohesive-frictional geomaterials including synthetics and soft rocks, like geopolymer (fly-ash) concrete and gypsum breccia, exhibit confining pressure dependence of both cohesive strength and characteristic strain at decohesion (cf. Gholampour et al., 2019; Deng et al., 2010, respectively). The present study investigates the confining pressure-sensitivity of cohesive-frictional geomaterials using a constrained optimization-based homogenization framework from Bryant et al. (2022), consistent with earlier theory including the micro-plane and granular micromechanics paradigms (cf. Weber, 1966; Dantu, 1968; Zienkiewicz and Pande, 1977). In particular, our framework defines an incremental variational principle that renders classical grain physics-based homogenization methods of hyperelasticity (e.g., cf. Bathurst and Rothenburg, 1988; Chang and Misra, 1990) extensible to plastic solids.
Creep Failure of Dry and Fluid-Saturated Rock
Authors: Bondarenko N. B. , Makhnenko R. Y. 
Published: September 2022

ABSTRACT:
Strength of the materials involved in the fluid injection is usually well assessed and injection pressure is maintained below the critical value to avoid induced seismicity. However, a microcracking activity could be triggered at stress levels well below the peak strength and could lead to rock failure in the long-term perspective, even if the effective stress state is not changing. Pore fluid could significantly affect the inelastic response and makes brittle creep in rock more pronounced. Triaxial creep tests are performed on dry and oil-saturated Berea sandstone specimens instrumented with strain gauges, LVDTs, and acoustic emission sensors. Recorded creep rate is highly correlated with the acoustic emission activity and sensitive to the experimental conditions (e.g., stress level). Dry and oil-saturated specimens exhibit similar behavior; however, some sensitivity to the type of the pore fluid and drainage condition is anticipated. Variation of the b-value might be one of the prognostic features for the transition between steady-rate and accelerating creep. Accurate representation of the in-situ condition in laboratory experiments is required for capturing the inelastic response of the material at constant subcritical stress level and addressing the long-term injection-induced seismicity.

1. INTRODUCTION
Many industrial activities involve subsurface fluid injection, which might be associated with an increased risk of earthquakes triggered by changes in the state of stress in the vicinity of the injection well (Ellsworth, 2013). The main mechanism for injection-induced seismicity is a reactivation of faults due to changes in pore pressure. However, it is recognized that many features of this process, such as seismicity triggered by pore pressure decrease (Van Thienen-Visser and Breunese, 2015) or triggering the largest earthquake after the termination of injection (Kim, 2013) cannot be explained by this approach and require consideration of coupled hydromechanical behavior (Segall and Lu, 2015). Strength characteristics of the involved rock formations are usually well-assessed before the injection, and the injection rate is selected to maintain the state of stress significantly below the critical value associated with reactivation of the favorably oriented faults. On the other hand, a microcracking activity could be triggered at stress levels well below the peak strength and could lead to rock failure in the long-term perspective, even if the changes of effective stresses are small (Heap et al., 2009). Rock deformation at constant stress that leads to delayed failure is called brittle creep (c.f., Scholtz, 1968; Brantut et al., 2013). Proper understanding of the creep processes is important for the characterization of mechanisms behind the seismic response observed during the fluid injection at relatively low pressures (Noël et al., 2019).
Triaxial Deformation Rate Analysis for Stress Estimation in the Sedimentary and Basement Rocks from the FutureGen Carbon Sequestration Project
Authors: Higgins J. , Lu Y. , Benge M. , Gunaydin D. , Bunger A. P. , Kelley M. 
Published: September 2022

ABSTRACT:
Deformation Rate Analysis (DRA) was carried out on rock samples from a characterization well at the former FutureGen2 site in Morgan County, Illinois. Although the experience with DRA reported in the literature is typically focused on shallower formations encountered in mining applications, the method was explored here using triaxial compression experiments for core retrieved from 1150-1350 meters depth. Consistent with past manifestations of the DRA method, core samples were subjected to two identical cycles of loading that started below the likely range of in-situ stress magnitudes and peaked above them, after which the core was unloaded in an identical manner to form a "saw-tooth" load/unload path. The inflections in the difference between the stress-strain relationship comprise the focus of the analysis. The inflection stresses closely follow vertical stress inferred from integrating the density logs for the vertically- oriented core plugs. The horizontal minimum stress inferred from horizontal core plugs matches well with bounds obtained by hydraulic fracture stress testing and corresponding to an average minimum tectonic strain of 170 microstrain. The maximum stress is found to track between the minimum horizontal and vertical stress in the sedimentary formations, implying a normal faulting regime. With a similar level of implied tectonic strain (average of about 350 microstrain), the maximum horizontal stress in the stiffer Precambrian Basement exceeds the vertical stress and implies strike-slip stress regime. Hence, the DRA method is found to be useful for bounding all three principal stress magnitudes and for detecting a shift in tectonic regime between units that was suspected but unable to be verified prior to these experiments.

1. INTRODUCTION AND BACKGROUND
Deformation Rate Analysis (DRA) is one of a variety of core-based methods for ascertaining in-situ stress. All such methods involve observing changes in the load-deformation behavior of a core that can be rationalized to relate to the previous stress to which the core was subjected before it was extracted from the subsurface. They bear the commonality that they rely on a well-known tendency of rocks to undergo inelastic and stress-dependent microstructural changes that provide a material memory of their stress history (e.g. Yamamoto et al. 1990, Kang et al. 2000, Villaescusa et al. 2002, Wu and Jan 2010).
Poroelastic and Adsorptive Properties of Activated Carbon
Authors: Guerrero J. O. , Espinoza D. N. 
Published: September 2022

ABSTRACT:
The characterization of petrophysical and geomechanical properties of source rocks presents inherent challenges due to lithology heterogeneity, lamination, distribution of organic matter, and presence of fractures. Organic-rich shales also present some distinctive features that make hydrocarbon production and CO2 geological storage unique in these rocks. The objective of this paper is to quantify and model the deformational behavior of carbon-based compounds due to changes of stress and pressure that happen simultaneously with gas adsorption and desorption processes. We designed an experimental procedure that consists of: (1) compaction of organic-rich grains/powder under oedometric conditions, (2) measurement of poromechanical properties in the absence of adsorption effects using helium in a triaxial cell through independent changes of confining pressure and pore pressure, (3) measurement of the adsorption strain, and stress for methane (CH4). An adsorptive-poromechanical model permits explaining the experimental data, discriminating between the strain/stress caused by poroelastic response from the adsorption-induced strain/stress, and measuring the poroelastic-sorption properties of the organic-rich compound. We applied this procedure to activated carbon and measured skeletal volumetric modulus ranging from 11.8 to 16.6 GPa and skeletal adsorption stress of ~100 MPa for CH4 at 7 MPa of adsorbate pressure. The proposed procedure and model are useful to explain and predict the unique properties of carbon-based adsorbents which can be extended to kerogen, a critical component in source rocks.

1. INTRODUCTION
Reserves estimation and gas flow rate prediction are more challenging for organic-rich rocks than for conventional gas reservoirs. These challenges are not only limited to characterization of petrophysical and geomechanical properties (i.e., lithology heterogeneity, lamination, total organic content and, the presence of fractures) but also to capturing the physics that governs these processes. Gas adsorption heavily affects the estimation of the original gas in place (Moore et al., 2012). Organic-rich surfaces can adsorb various gas molecules (N2, CH4 and CO2 among others) increasing vastly the storage capacity in organic-rich rocks (Busch and Gensterblum, 2011).
Concrete Fracture and Stress Analysis Using the Combined Finite-Discrete Element Method in the Brazilian Tension Test
Authors: Padilla A. , Rougier E. , Knight E. , Reda Taha M. M. , Stormont J. C. 
Published: September 2022

ABSTRACT:
Numerical modeling techniques using the combined finite-discrete element method have been utilized to explore the relationship between stress, damage, and crack propagation in concrete. Obtaining post-peak behavior from the Brazilian tension test is difficult because failure occurs abruptly. An experimental test method is described which enables monitoring of the post-peak cracking behavior in the Brazilian tension test by slowing the crack propagation. Experimental testing with this technique proved its capabilities in slowing crack propagation. The combined finite-discrete element method is used to further examine the stress states during this test and to understand the damage evolution present in this test prior to the peak strength. The method also allows for interpretation into the type of damage present throughout the entire test and the zones in which that damage initiates. A comparison is also performed between the numerical results and experimental observations to determine how well the numerical method captures the experimental results. This work enables a good understanding of how fractures form in the Brazilian tension test as well as a comparison between experimental and numerical technique results.

1. INTRODUCTION

1.1. Combined Finite Discrete Element Method
In an effort to model inelastic behavior and predict the deformation and failure of materials, the combined finite discrete element method has been employed. The finite-discrete element method (FDEM) is an innovative numerical computation method that combines the efficiency of the finite element method (FEM) with the discontinuity framework of the discrete element method (DEM) to create a highly powerful and efficient system (Munjiza et al., 1999; Rougier et al., 2014). The comparison of DEM and FEM with a schematic visualization of FDEM is shown in Fig. 1. At the contact interfaces of the FDEM framework, there is bonding. The bonding is numerically represented with cohesion points along the boundaries of the deformable particles (Rougier, Knight, Lei, et al., 2014). The cohesion of these bonds is a combination of normal cohesion and tangential cohesion. When the material is exposed to significant stress, these bonds become strained and can become unbonded (Rougier, Knight, Lei, et al., 2014).
Prediction of Mud Loss Type Based on Seismic Data Using Machine Learning
Authors: Pang Huiwen , Wang Hanqing , Jin Yan , Lu Yunhu , Fan Yongdong 
Published: September 2022

ABSTRACT:
Mud loss is one of the most common and troublesome wellbore problems. Predictive evaluation of mud loss types not only optimizes drilling design, but also reduces potential costs before drilling. To solve mud loss problem of M formation in the H oil field, we proposed a practical solution based on machine learning in this paper, which can predict the mud loss types using seismic data. Firstly, we calculated and obtained 16 seismic attributes in 6 categories, and according to the mud loss rate and volume, we classified the mud loss into 4 types: seepage loss, partial loss, severe loss, and total loss. Then 10 typical wells were selected from 50 wells, which covered different mud loss types and depth. The seismic attributes of single well with the above characteristics were extracted, and the relationship between seismic attributes and mud loss type were obtained using machine learning. Finally, a 3D probability prediction model of potential mud loss type is obtained and analyzed with a practical case. Our model can predict the distribution of mud loss types at different depths in different regions. It can not only be used in the design of well location and well trajectory but also provide scientific suggestions for mud loss prevention and plugging.

1. INTRODUCTION
Mud loss is one of the common downhole problems during drilling and completion. It not only causes a significant increase in non-productive time (NPT), but also increases well control risk (Sun et al., 2021). When drilling in the carbonate formation, mud loss has become the primary problem affecting safe and efficient drilling due to the complex and changeable leakage zones (Savari and Whitfill., 2019; Huang et al., 2020). Therefore, mud loss prediction of carbonate formation has become a hotspot and "Difficult topic" in current research.
Estimation of Mechanical Properties of Mancos Shale Using Machine Learning Methods
Authors: Kadeethum Teeratorn , Yoon Hongkyu 
Published: September 2022

ABSTRACT:
We propose the use of balanced iterative reducing and clustering using hierarchies (BIRCH) combined with linear regression to predict the reduced Young’s modulus and hardness of highly heterogeneous materials from a set of nanoindentation experiments. We first use BIRCH to cluster the dataset according to its mineral compositions, which are derived from the spectral matching of energy-dispersive spectroscopy data through the modular automated processing system (MAPS) platform. We observe that grouping our dataset into five clusters yields the best accuracy as well as a reasonable representation of mineralogy in each cluster. Subsequently, we test four types of regression models, namely linear regression, support vector regression, Gaussian process regression, and extreme gradient boosting regression. The linear regression and Gaussian process regression provide the most accurate prediction, and the proposed framework yields R2 = 0.93 for the test set. Although the study is needed more comprehensively, our results shows that machine learning methods such as linear regression or Gaussian process regression can be used to accurately estimate mechanical properties with a proper number of grouping based on compositional data.

1 INTRODUCTION
The hydro, mechanical, and chemical properties of shale formations with compositional and textural heterogeneity across a range of scales give rise to very complex behavior under various environmental and engineered conditions. Various geologic variables, including mineralogy, types of cement, organic content, and the spatial distribution of these characteristics, contribute to mechanical properties (elastic properties, fracture toughness, anisotropy, etc.). These compositional and structural heterogeneity in very-fine sedimentary rocks may affect the onset and propagation of brittle fracture in shale and can lead to the formations of flow conduit. Given the formation and operational conditions (e.g., stress, natural fractures, injection fluid and pressure) the geometry and extent of fracture networks is predominantly determined by shale mechanical properties.