bluuebunny/crossref_metadata_2025 huggingface dataset:
Critical Crack Opening of Charcoal Granite
Authors: Fakhimi A. , Asem P. , Tarokh A. , Labuz J. F.
Published: September 2022

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

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

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

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

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

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

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

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.
Heat Extraction and Interlayer Interference in Heterogeneous Multi-Layer Commingled Production Oil Reservoir
Authors: Xu Fuqiang , Song Xianzhi , Song Zihao , Wang Gaosheng , Shi Yu
Published: September 2022

Geothermal development of oil reservoirs using abandoned or high water-cut wells has received a lot of attention. The heterogeneity is a common feature of oil reservoir, and it cases the production characteristics are distinct. We have established a coupling model of oil-water two-phase heat flow in the heterogeneous multi-layer commingled production reservoir. The model considers local thermal non-equilibrium (LTNE) and is a dual porosity model, which can be used to describe the fluid flow in the fractured reservoir. Using the model, the effects of different reservoir characteristics and injection parameters on production characteristics are analyzed. Reservoir characteristics include dip angle, cubic matrix block side length, and injection parameters include injection temperature and mass flow. Under the conditions studied in this paper, after 5 years, the maximum differences of production temperature and deviation values can reach 27.5 °C and 65.34% at different injection mass flow, respectively. The maximum deviation value difference can reach 45.90% at different cubic matrix block side length, while the impact on production temperature is small. The injection temperature and dip angle have a relatively small impact on the above production characteristics. This study has certain significance for the application of geothermal energy in oilfields.

1. INTRODUCTION

Geothermal energy is one of the important renewable energy sources, with advantages such as features weather independence, stable, operationally reliable, and environmentally friendly nature (Wang et al. 2018). Compared with the utilization of shallow geothermal energy, the high drilling cost has led to the slow development of mid-deep geothermal resources. Many oil reservoirs have produced liquids with water content of more than 95% and have become "hydrothermal geothermal fields". Some oil wells in high water-cut oil fields have reached their economic limits and have even been abandoned. The oilfield area usually has a high geothermal gradient, and many abandoned wells have abundant geothermal resources, such as Texas, Oklahoma, Louisiana and North Dakota in the United States, and Songliao Basin, Bohai Bay Basin, and Ordos Basin in China (Augustine and Falkenstern 2014; Jiang et al. 2019). Using abandoned oil wells to develop geothermal energy can alleviate the pressure of energy supply and demand, save drilling and sealing well costs, and control the pollution of abandoned wells (Cheng et al. 2016; Lin et al. 2021).
Experimental Study on Water Absorption Characteristics of Interbedded Lithology in Low Permeability Reservoir
Authors: Fang Zheng , Chen Mian , Yin Daiyin , Yu Yanbo , Si Xiang , Yang Kang
Published: September 2022

In the development of low permeability reservoirs, long-term high pressure water injection leads to the formation of high conductivity water-injection induced fractures and the injection water into the non-reservoir lithologic section has also been found in the field inspection well sampling. However, the previous core evaluation is mainly based on reservoir lithology, and the water absorption characteristics of barrier and interlayer lithology and its influence on development effect were not clear. In view of the above problems, this paper takes Daqing Chaoyanggou oilfield as an example, studies the longitudinal lithologic distribution characteristics according to the field logging data and coring data, and statistics the main lithology in the non-reservoir lithologic section of Chaoyanggou oilfield. The water absorption characteristic experiment was carried out and the relevant reservoir parameters were clarified. Numerical simulation of reservoir considering interlayer water absorption is carried out by using Eclipse. The research results show that mudstone basically has no permeability, saturated water absorption coefficient increases with the increase of injection end pressure, and decreases with the increase of injection end to sample center distance. Silty mudstone has a certain permeability and water absorption characteristics between mudstone and argillaceous siltstone, and there is a phenomenon of fluid pressure transmission in the pores. The water absorption characteristic of argillaceous siltstone is consistent with the compression characteristics of fluid. The numerical simulation results of reservoirs with compartments are also more accurate, which explains the high injection-production ratio but low production in low permeability reservoirs. The results of this study have certain guiding significance for the efficient development of low permeability reservoirs.

1. INTRODUCTION

Low permeability reservoir is characterized by small pore and throat radius, complex pore structure, low reservoir permeability and strong longitudinal and plane heterogeneity. In the process of development, there are common phenomena such as high injection-production ratio and difficult to establish effective drive system [1-4]. Recent field sampling has also revealed that injected water has penetrated into the interbed(Fig.1), which, combined with the physical and development characteristics of low permeability reservoirs, may be due to long-term high-pressure water injection, which has caused waterflooding induced fractures in the reservoir and caused the injected water to penetrate into the interbed [5]. However, the factor of lithologic water absorption of interbed is not taken into account when formulating development strategy and calculating development index.
Estimation of Fluid Flow Boundary Conditions: The Role of Pressure Transient Analysis in Safe CO2 Sequestration and Underground Storage
Authors: Amirlatifi Amin , Eckert Andreas , Nygaard Runar
Published: September 2022

Conducting safe and effective waste disposal and sequestration processes relies on an accurate determination of the reservoir extent and the prevailing boundary conditions. Due to the limitations surrounding the acquisition and analysis of the reservoir geometry, waste disposal, cuttings re-injection, and CO2 sequestration studies are based on simplifying assumptions regarding the lateral and vertical fluid flow boundary conditions. These assumptions can jeopardize the study’s outcomes, especially for green fields. Common boundary conditions considered are limited to either open (steady-state) or closed (semi-steady state) lateral boundaries, alongside a complete or partially sealing caprock. This study uses pressure transient analysis to provide a quantitative tool to assess a wider variety of fluid flow boundary conditions. We show that a short drawdown followed by a pro-longed buildup test can identify the fluid flow boundary condition, including closed, open, semi-open, and infinite systems. The significant difference in CO2 storage capacity and the different geomechanical risks associated with various fluid flow boundary conditions suggest that the presented methodology should be considered prior to fluid injection scenarios.

1 INTRODUCTION

Geologic sequestration is an increasingly important strategy to dispose of drilling fluids, saltwater, and hazardous waste and to reduce the CO2 concentration in the atmosphere (Mortezaei et al., 2021). The most viable CO2 sequestration targets include deep saline aquifers and mature hydrocarbon fields (Garcia et al., 2010; Sarhosis et al., 2018; Bachu, 2003; Holloway, 2001; Holloway and Savage, 1993; Klara et al., 2003). The fluid flow boundary conditions of the target storage medium need to be known to predict the target formation’s storage capacity, the spreading of the injected plume, and the geomechanical risks associated with the pore pressure increase. The current practices commonly consider an assortment of simplified boundary conditions that include open and closed boundaries when it comes to sequestration.
Feasibility Study and Design of an Underground Entry/ Access Structure at an Underground Gold Mine
Authors: Carlisles B. B. , Koroznikova L. , Javidan F. , Khandelwal Manoj
Published: September 2022

This paper investigates the viability of an increase in waste rock storage by backfilling the Falcon pit and extending the portal of the Fosterville gold mine, located in Bendigo, Australia. The structure will maintain the current access to the tunnel whilst developing a fillable void. Once completed the project will allow for a total increase of 900,000 cubic metres of storage. Furthermore, a finite element study has been conducted to investigate the structural performance of a proposed design using corrugated steel sheets. Stresses and displacements are studied taking into account various design factors such as steel properties and geometry. Results demonstrate the location of critical stress values according to the proposed design. The selection of optimum steel geometry is also investigated with regards to the factor of safety.

1. INTRODUCTION

Gold mining has been a part of Bendigo’s history since the discovery of the first deposits of alluvial gold by Kennedy and Farrell in 1851. Fosterville, one of the gold mines in the area, is located 20 kilometers out of Bendigo, Australia.

Gold was first found in Fosterville in 1894 and during 9 years of operation 0.87 t of gold was produced. Mining of shallow oxide opens pits re-commence in 1991 using a heap leach operation process, which ceased in 2001. A feasibility study into sulphide gold-bearing ore processing was completed in 2003 and the first stage of commercial production began in 2005. The operation started by extracting low-grade, near-surface mineralization (Table 1) (T Fuller & Hann, 2019).

Fosterville’s deposit is hosted within an interbedded turbidite sequence of sandstones, siltstones and shales. The primary gold mineralization follows disseminated arsenopyrite and pyrite forming as a selvage to veins in a quartz-carbonate vein stockwork. The deposits have average grades of 5-10 g/t Au (Fig. 1). The sulphide mineralization is overprinted by visible gold within-host quartz veins. Visible gold is becoming more frequent at depth and with the discovery of the Eagle zone and soon after the Harrier zone (Fig. 1), these deposits are high-grade (2.29 Mt @ 23.1 g/t Au) (Table 2), reaching the highest assays seen in recent history, 191 g/t Au over 2.55 m in the Swan zone. Visible gold is observed within quartz-carbonate veins, with a noticeable increase in recent years as underground mining has advanced deeper. Visible gold particles are predominantly specks (up to 3mm), however more rarely they can be > 5mm (T Fuller & Hann, 2019).
Effect of Multiple Loading Rates on Uniaxial Compressive Strength of Rock
Authors: Meerza J. B. , Khandelwal Manoj
Published: September 2022

It is of crucial significance to study the effect of loading rate on the behaviour of rock because engineering structures are subjected to multiple loading conditions in their entire life. Although rock behaviour under single loading rate has been widely studied but very limited research has been conducted to study the performance of rock strength subjected to multiple loading conditions. This paper presents an experimental study of the effects of single and multiple strain rates on Sandstone samples. The first set of samples was tested at constant strain rates until failure to determine the peak uniaxial compressive strength (UCS). For the second set of samples, the first strain rate was applied to the sample up to a predetermined load, and then the second strain was initiated to find out the influence of multiple loading rates on the UCS of rock samples.

1. INTRODUCTION

Geo-mining engineering deals with the extraction of minerals from the earth’s crust with the application of science and technology. Mining activities can cause severe disturbance in the natural environment, which results in the loss of hundreds of lives. For example, the misunderstanding of rock’s physical and mechanical properties in mining may lead to severe geological disasters which are to occur during the mining extraction process. Therefore, mining engineers must be concerned not only with the production and processing of minerals but also should anticipate the damage to be caused to the environment both during and after the extraction process in mining. Rock physical and mechanical properties are very important parameters for the safety and stability of any geo-mining engineering design and construction (Cheshomi et al, 2015; Khandelwal and Ranjith, 2017).

There is an increasing trend towards infrastructural development all over the world. The extraction process of minerals from the earth’s crust may cause disturbance in the natural environment and may lead to geological disasters due to the misunderstanding of geo-mechanical properties (Du et al, 2020). Therefore, it is of great importance to investigate the effect of multiple loading rates on the uniaxial compressive strength of rock (Lajtai, 1991; Zhang et al, 1999, 2000; Khandelwal et al, 2013; Wang et al, 2020). These engineering structures are made either on the rock mass or in the rock mass. There is no denying the fact that engineering materials are subjected to multiple loading rates during their whole life (Li et al, 1998). The effects of single and multiple loading rates on strength with stress characteristics of rocks are important in defining input loading which is used in the mining designs. The effects of different strain rates have significant effects on the process of rock breakage as well as peak strength value (Olsson, 1991). Although material behaviour under a single loading mode has been extensively studied, very limited research has been conducted to investigate the performance of brittle materials subjected to varying loading conditions.
Design of Larger Span Overhanging Cliffs Constructed in Himalayas
Authors: Emad M. Z. , Waqas M.
Published: September 2022

Road construction and maintenance is challenging in Himalayan region of Pakistan. The operators must deal with slope stability issues and falling rocks. In addition, the slope heights are huge that have a greater impact on economics and feasibility of operations. To deal with this situation the contractors create a slot (or overhanging cliff) in the base of the slope, especially in competent rock. These address some of the issues like reduced excavation costs and avoiding tumbling rock falls from top of the slope. Thus, it reduces overall excavation cost and construction time. While the occasional fall of rocks and debris on the highways is diverted by hanging cliff or rock cover, the construction design of these structures is purely based on experience. The problem add-on when an expansion in span or height is desired in existing roads. This paper summarizes the stability study of overhanging cliffs and evaluates its design in challenging ground. An extension of a national highway case study for existing span of 7 m tunnel is studied. Numerical modeling is used to study the stability of road overhanging cliff. Different scenarios are modeled in consultation with the field practitioners and a stable design is proposed for extension.

1. INTRODUCTION

Overhanging rock slopes are excavated in hard rocks along steep hill side roads. It looks like a half tunnel whose one side is open on the valley side as presented in Figure 1. The crown remains hanging or cantilevered with tunnel having one abutment. These structures are constructed in very strong rocks of Himalayan regions of South Asia (Anbalagan et al., 2003). Similar structures can be found in United States, Europe, Saudi Arabia, and Philippines. Construction of highways and roads along steep hillside is challenging. It is easier to excavate a smaller portion of rock. In Himalayas natural slope heights ranges up to more than 5000 m with slope angles up to 70 degrees (Ali et al., 2019). Generally, the excavation of such a slope will require excavation and creation of benches for stability. This will automatically increase project costs and will not help much with maintenance later. Many other issues like sliding, low safety, rock falling, and frequency of accidents during construction may arise (Terzaghi, 1962). The overhanging structure is not anyway near to the conventional tunneling. It is based on hit and trial and no scientific input is there. Also, the literature is silent on scientific design of such structures. A few references (Paronuzzi and Serafini, 2009; Schlotfeldt et al., 2018; Tokashiki and Aydan, 2010; Tsesarsky and Hatzor, 2009) studied some features and stability assessment of overhanging cliffs.
Effect of Chamfer Geometry of PDC Cutters on the Impact Resistance, Wear Resistance and Rock Cutting Efficiency
Authors: Wei Jiusen , Hu Guiyu , Shi Xiaolei , Shao Fangyuan , Liu Wei , Gao Deli
Published: September 2022

Polycrystalline diamond compact (PDC) drill bit is widely applied in drilling engineering. Under harsh downhole conditions, the quasi-brittle characteristics of PDC cutters may be a severe drawback of drill bits, which readily causes premature impact failure. In order to improve the durability of PDC cutters without compromising the cutter aggressiveness, the planar diamond table with modified cutter edge geometry was experimentally investigated. The experiment included progressive drop test (PDT) and vertical turret lathe (VTL) wear test. The cutting forces were measured using a dynamometer load cell. Overall test results were compared together. The results showed that a single-chamfer cutter performs best under the dry VTL test without coolant and generates a lower cutting force. The dual chamfer geometries showed a significant impact resistance without compromising other properties. Because the commonly used mechanical specific energy (MSE) has a negative relationship with cutting efficiency, therefore, the ratio between the volume of rock cuttings and energy consumed on rock cutting process was calculated to represent the cutting efficiency or namely aggressiveness, so as overall analysis performances with same correlation trend between cutting edge geometry and cutter properties. From the overall comparison, it is found that cutters with a sharper edge can enhance the aggressiveness but has a worse impact resistance; Cutters with complex and large edge size bring a good impact resistance but lead to lower aggressiveness.

1. INTRODUCTION

It is well known that PDC drill bits are becoming more widely used to drill oil & gas wellbores. As the key component of PDC drill bits, PDC cutter is composed of a polycrystalline diamond layer and a cobalt-cemented tungsten carbide substrate. The PDC cutter is sintered under high-pressure (typically 5-8 GPa) and high-temperature (typically 1400-1650 °C) conditions. During sintering, the cobalt that existed in the substrate turns molten and wets through the diamond powder bed at a short duration. All diamond particles are then bonded together to form a solid polycrystalline structure (Shin et al. 2004; Hong et al. 1991; Akaishi et al. 1991). Enhancing the physical properties of PDC cutters will undoubtedly make the bits drill faster and deeper. The physical properties of PDC cutters play an important or even predominant role in the drilling performance of PDC bits.
Energy Partitioning During Fracturing in Granite Under Stress Relaxation
Authors: Zafar Sana , Hedayat Ahmadreza , Moradian Omid
Published: September 2022

Time-dependent deformation affects the fracturing in rocks and can reduce their failure strength. Such time-dependent deformations are important for surface and underground structures, which are typically designed for long operational time. The weakening of rock with time is directly related to the evolution of microcracks and in this study, we focused on the micromechanics of the fractures produced in crystalline rocks under time-dependent loading conditions. Stress relaxation experiments were conducted on double-flawed prismatic Barre granite specimen in the laboratory to investigate the fracturing processes in terms of the source mechanics and the source physics. Absolute calibration of the AE sensors was performed in the laboratory to identify individual sensor responses for a known source (ball drop). Source parameter analysis was undertaken using spectral fitting method obtained for the displacement spectra at each source location. Corner frequency and seismic moment were determined, ranging from 350 kHz to 650 kHz and 10−4 to 10−1, respectively. Finally partitioning of input and output energies during the fracture propagation under monotonic and multistage relaxation loading conditions was determined. Results suggest that the amount of radiated seismic energy during multistage relaxation experiments is almost the same as in the monotonic loading experiments, however, the number of cracks produced in case of multistage relaxation is higher than that of the monotonic loading experiments.The finding of this study can help us to better understand the fracturing processes in the various field applications dealing with time-dependent failure in rocks.

1. INTRODUCTION

Time-dependent behavior can be described as a phenomenon caused by the weakening of a rock mass with time, such as creep, consolidation/dilation, swelling, and stress relaxation. A detailed knowledge of the time-dependent behavior of rocks is important to predict the long-term stability of underground structures (Diederichs and Kaiser, 1999), surface structures and rock slopes (Yu et al., 2012; Zhang et al., 2020), and nuclear waste repositories (Nara et al., 2010).
Microscale Investigation of Strength and Failure Behavior of Rock-Concrete Interfaces Under Tensile Loading
Authors: Shams G. , Rivard P. , Moradian O.
Published: September 2022

Tensile failure and detachment of rock-concrete interfaces in civil engineering structures such as gravity dams is considered as one of the critical factors in controlling the stability of these structures. Despite the large number of studies, the fracturing process along the rock-concrete interfaces under tensile loading is not yet well understood. In this study, digital image correlation and acoustic emission techniques were employed to investigate the effect of the interface on the strength and the fracture properties of granite-mortar specimens under tensile loading. Our results indicated that the tensile strength of the granite-mortar interfaces was smaller than that of either the granite or the mortar. It was found that the tensile strength of the interface was controlled by both interface (adhesive strength) and the mortar (cohesive strength). The DIC results showed that FPZ is mainly limited to a narrow band along the interface, while the AE analysis revealed that the FPZ covers the interface area and a considerable portion of the mortar. AE better illustrated that the fracture may initiate at the interface and then kink into the mortar. In addition, it was seen that the surface roughness of the generated fractures is material dependent, i.e., fractures generated in granite were roughest, while fractures formed along the interface had the lowest roughness values. The finding of this study can improve our understanding of the tensile strength and behavior of rock-concrete interfaces, leading to the safer design of engineering structures.

1. INTRODUCTION

In geomechanics, rock-concrete interfaces are frequently seen in civil and mining engineering applications such as tunnel linings, concrete gravity dams, concrete retaining walls, socketed piers, and shotcrete as a support for rock mass (Fishman, 2009; Chang et al., 2018). In such structures, the interface between rock and concrete is usually considered as the weakest structural zone, causing the initiation and growth of cracks and final failure along the interface (Zhong et al., 2014; Dong et al., 2019).
Rock-Discontinuity-Fragmentation (R-Dis-Frag): A Computer Package for the Characterization of Large-Scale Fractured Rock Masses in Real-Time
Authors: Hekmatnejad A. , Crespin B.
Published: September 2022

Rock block geometry (size, frequency, and shape) is an important characteristic in many rock engineering studies including rock mass classification, discrete element method, surface and underground stability analysis, drilling, blasting design and hydro-geological analyses. There are several polyhedral modelers available, but the limited computational capacity is one of the main issues when dealing with the characterization of real scale fractured rock mass up to millions of fractures at a real engineering time scale. This paper presents a novel approach for a voxel-based polyhedral modeler, optimized to exploit the computing parallelism of graphics processing units (GPUs). In this approach, there is no limitation for the complexity of rock blocks, fracture shapes, and excavation surfaces with complex morphologies. The computational time for the geometrical characterization of rock blocks for a 100-meters cubical domain with 2000,000 fractures is less than 3 minutes.

1. INTRODUCTION

One of the most important sources of uncertainty for the evaluation of fractured rock mass behavior is the "block geometric uncertainty" which plays a critical role in the design of underground and surface opening. According to the literature review, the most significant discrete fracture network parameters when analyzing block geometry uncertainties are orientation, size, topology, volumetric intensity, and 3D mechanical connectivity (Rodriguez and Sitar, 2008; Wang et al, 2013; Zheng et al., 2015; Li et al., 2018, Hekmatnejad et al., 2021). If fractures in the rock mass cannot be fully described in 3D, uncertainties appear in the block formation and block geometry (size, shape, location), which in turn create another kind of uncertainty – that of driving force and resistance force; it also affects the amount of required support in tunneling application and the probability of hanging up occurrences at draw points in cave mining. When considering a discrete fracture network model, the most fundamental and important step is the identification of complex formed blocks, their geometry, and even their stability states (block stability analysis) for instability analysis around the surface and underground excavations (see Figure 1).