Rock Structure Research Articles

Analysis of deformation and failure of sediment particle-surrounding rock structure of salt cavern gas storage under the coupled action of temperature and pressure

When gas is injected or produced in the gas storage of salt cavern, the different effects of thermal stress, gas pressure, sediment particles and brine pressure on the cavity wall of salt cavern may cause large deformation and damage in the surrounding rock, which threatens the safe and stable operation of the gas storage of salt cavern. Therefore, based on FLAC3D-PFC3D coupling method, a numerical model of salt cavern gas storage with sediment particles in consideration of temperature was constructed, and the influence of injection-production time effect, sediment particle size and initial porosity on the deformation and failure of sediment-surrounding rock structure is studied. The results show that the tensile contact force chain of sediment is sensitive to the particle size of sediment, but insensitive to the initial porosity of sediment and injection-production conditions; during gas production, the larger the particle size and initial porosity of sediment particles, the greater the vertical displacement of shallow sediment particles, and the opposite results are obtained during gas injection. With the progress of gas production and gas injection, the absolute value of vertical displacement of the roof of the salt cavern increases gradually, and the plastic failure range of surrounding rock expands; for gas production process, the larger the particle size and initial porosity of sediment, the smaller the algebraic value of vertical displacement of surrounding rock at the top of cavity and the smaller the plastic failure range of surrounding rock. For the gas injection process, the larger the particle size and initial porosity of the sediment, the larger the algebraic value of the vertical displacement of the surrounding rock at the top of the cavity and the larger the plastic failure range of the surrounding rock. The results can provide reference for the reasonable setting of injection-production operation parameters of salt cavern gas storage and ensure the safe and stable operation of underground salt cavern gas storage (USCGS).

Reliability Analysis of High-Pressure Tunnel System Under Multiple Failure Modes Based on Improved Sparrow Search Algorithm–Kriging–Monte Carlo Simulation Method

It is often difficult for a structural safety design method based on deterministic analysis to fully and reasonably reflect the randomness of mechanical parameters, while the traditional reliability analysis method has a large calculation cost and low accuracy. In this paper, based on the seepage–stress coupling numerical model, the random variables affecting the reliability of the collaborative bearing of surrounding rock and lining structures are successfully identified. Then, the improved sparrow search algorithm (ISSA) is used to optimize the hyper-parameters of the Kriging surrogate model, in order to improve the computational efficiency and accuracy of the reliability analysis model. Finally, the ISSA-Kriging-MCS model is used to quantitatively evaluate the reliability of the surrounding rock-reinforced concrete lining structure under multiple failure modes, and the sensitivity of each random variable is discussed in depth. The results show that the high-pressure tunnel structure has high safety and reliability. The reliability indexes of each failure mode decrease with the increase in the coefficient of variation (COV) of random variables. In addition, the same random variable also exhibits varying degrees of influence in different failure modes.

The Influence of the Key Characteristics of Overburden Rock Structure on the Development Height of Water-Conducting Fracture in Yushenfu Coal Mine Area, China

The destruction of shallow aquifers by water-conducting fractures of overlying strata caused by underground coal mining is the most representative form of mining-induced damage in the Yushenfu mining area. It has become an important factor restricting the green mining of coal in the Yushenfu mining area and even the ecological protection and high-quality development of the middle reaches of the Yellow River. As the key scientific problem of water-preserved coal mining, the scientific understanding of the development law and main influencing factors of water-conducting fractures in overlying strata has attracted great attention. Taking the geological occurrence characteristics of the main coal seam in Yushenfu mining area as the prototype, 24 different types of numerical models are constructed with the key characteristics of the overburden structure, such as the number of layers of sandstone in the overburden (sand layer coefficient) and the thickness ratio of sandstone and mudstone in the overburden (sand–mud ratio), as the main variables. By means of numerical simulation experiment and theoretical calculation, combined with field measurement and comparison, the influence of the key characteristics of overburden structure on the development height of water-conducting fracture is studied and revealed. It is proposed that the effective area for the study area to achieve water-preserved coal mining by using the height-limited mining method must conform to the coal seam overburden structure characteristics of “sand–mud ratio 6:4 and sand layer coefficient less than 70%” and “sand–mud ratio 8:2 and sand layer coefficient less than 80%”. The results not only enrich and deepen the research on the influence of geological factors and the law of controlling the development of water-flowing fractures in overlying strata, but also provide theoretical support for the precise protection of groundwater resources in the Yushenfu mining area in the middle reaches of the Yellow River.

Investigation on the transmission of Love waves due to an impulsive line source in a heterogeneous double porous rock structure.

The region around the reservoir sometimes encounters the seismic response of ground. The phenomena of Love waves propagation also caused by seismic activity which can further significantly influenced by an impulsive line source present in the rock structures of ground. The current study elucidates the propagation behavior of Love waves induced by an impulsive line source within the anisotropic layered heterogeneous double porous rock structures commonly found in proximity to the reservoir areas. The expression of the dispersion relation for the Love waves propagation due to an impulsive line source has been derived by using the Fourier transformation and Green's function technique. The above-mentioned rock composite structure is consisted of two different portions: upper transversely isotropic double porous (TIDP) layer medium and lower heterogeneous isotropic double porous half-space (IDP) medium. In the aforesaid half-space medium, both types of heterogeneities viz. linear and quadratic have been considered. The impacts of heterogeneity parameters associated with the lower heterogeneous IDP half-space, porosity parameter (corresponds to both upper TIDP layer and lower IDP half-space) and anisotropic parameter of TIDP layer on Love waves phase velocity have also been studied. Some special outlines have also been depicted graphically.

Environmental effects of acid mine drainage and rehabilitation options at closed mine site: a case study.

Irregular waste storage at closed mine sites poses severe environmental problems. This study evaluates the concentrations and effects of trace elements released into the environment by mining activity by analyzing soil, water, and sediment samples taken from a copper mining site. According to the data, acidic mine drainage was the main cause of the high concentrations of trace elements in the soil and sediments, including arsenic (As), cadmium (Cd), lead (Pb), and copper (Cu). The concentrations of As, Cd, Pb, and Cu in soil and sediments were 2734-times, 1189-times, 157-times and 32 times higher, respectively, in comparison to the background values of averaged concentrations of these elements in the upper crust. Geological and statistical studies indicate that the primary constituents of these pollutants are chalcopyrite and pyrite derivatives present in the primary rock structure. Using water analysis data from 2011 to 2020, the release of essential trace element into water was investigated to monitor the environmental effects of acidic mine drainage (AMD) from the closed Kuvarshan copper mine in the Artvin region of Turkey. This study demonstrates that trace elements concentrations may change according to local and seasonal factors and highlights the importance of conducting routine environmental monitoring studies.

Evaluating the water resistance performance of coal seam floor rock mass using VW–NC model

The rock mass of coal seam floor plays a crucial role in blocking the uplift and runoff of the underlying confined water in the course of mining under water pressure. Accurately assessing its water resistance performance, which is influenced by numerous factors, is important for preventing accidents caused by inrushing water. This study focuses on a coal mine in the Ningwu coalfield in North China. We establish an evaluation system for the water resistance performance of coal seam floor rock mass, using indices including rock mass thickness, lithological combination characteristics, rock mass quality, structure complexity and bedding plane count. A variable weight–normal cloud (VW–NC) model is formulated to quantitatively evaluate the water resistance performance of the coal seam floor rock mass. Comparative analysis with actual mining conditions and other models reveals that the VW-NC model provides the most precise and accurate results. The study finds that the primary influencing factors on the water resistance performance are weak structural planes, including faults, joints, and bedding planes. The proportions of strong, relatively strong, relatively weak, and weak zones in research area are 20.41%, 59.88%, 12.38%, and 7.33%, respectively.

Fracture Mode and Thermal Damage Evolution of Sandstone Under the Coupling Effect of Thermal Treatment and Impact Load

The dynamic properties of high-temperature sandstone quickly deteriorate with different cooling methods, which leads to the instability of underground engineering rock structures. Therefore, it is of great significance to quantify the changes in the dynamic characteristics of high-temperature cooled sandstone under impact loads. Therefore, the sandstone is heated to different temperatures and cooled using three methods. A dynamic tensile test is performed using the Splitting Hopkinson Pressure Bar (SHPB) test set for high-temperature cooled sandstone. At the same time, the transient process of rock failure was examined using high-speed cameras. The influence of different temperatures and cooling methods on the thermal damage value of sandstone was analyzed, and the prediction equation was formed. The change in rock energy during rock failure under impact load was calculated.

Increasing accuracy in predicting mode I fracture toughness of rock structures: a comparative analysis of the rock engineering system method

The investigation of crack initiation and expansion is vital for the stability of structures. The Mode I fracture toughness (KIc) of rocks is a key property used to predict crack propagation in tension and hydraulic fracturing. Various methods have been introduced to determine KIc, but results differ due to factors like sample dimensions, crack geometry, groove type, and loading conditions. The cracked chevron notched Brazilian disc (CCNBD) sample is commonly used in laboratory tests for its easy preparation. This study employs the rock engineering system (RES) technique to overcome the challenges of time-consuming and costly laboratory tests and the uncertainty in traditional methods (analytical, numerical, experimental, laboratory, regression). Using 88 CCNBD rock samples proposed by ISRM, input parameters include thickness of the disc specimen (B), uniaxial tensile strength (σt), initial crack length (α0), radius of the disc specimen (R), crack length (αB), and the length of the final crack (α1). The RES-based model used 70 data points (80% of the dataset) for development, and 18 data points (20%) for evaluation. Regression analysis compared the performance of the RES method, using statistical indicators such as squared correlation coefficient (R2), mean square error (MSE), and root mean square error (RMSE) to measure accuracy. The RES-based method outperformed other regression techniques, demonstrating significantly enhanced accuracy. This highlights the effectiveness and superior performance of the RES method in estimating fracture toughness, particularly for CCNBD samples, showcasing its potential as a robust analytical tool.

The role of hydrothermal alteration in uranium mineralization at the Xiaoshan uranium deposit, South China

Hydrothermal alteration can be utilized to constrain element migrations during mineralization, as it records the effects of fluid-rock interactions. Previous studies have suggested that uranium in deposits primarily originates from uranium-bearing granites; however, limited knowledge exists regarding the leaching mechamisms of this element and rare earth elements (REEs) from these rocks. In recent years, the Xiaoshan Deposit, a newly discovered medium-sized uranium deposit, has been discovered in the central part of the Lujing uranium ore field, South China. In this study, we examine this deposit to investigate hydrothermal alterations and their impact on elemental mass change. The deposit exhibits seven types of alteration including K-feldspar, albite, illite, sericite, muscovite, quartz and chlorite alteration. These alterations follow a certain sequence, starting from chlorite alteration, followed by widespread K-feldspar alteration, then to albite alteration, accompanied by muscovite alteration, and finally illite, sericite and quartz alteration. The main uranium mineralization stage was coeval with the late acid siliceous hydrothermal fluid, illite and sericite alteration. The pre-ore alkaline alteration (K-feldspar alteration) resulted in the leaching and extraction of uranium, leading to the precipitation of a significant amount of apatite in mineral interstices and initial uranium enrichment (ΔCi (U) = 16.52 ppm). This process facilitated material preparation for subsequent acidic alterations and localized ore enrichment. The original dense rock structure was disrupted, creating fractures/cavities that served as conduits for uranium mineralization. Moreover, under alkaline metasomatism, uranium and REEs was extensively leached out of uranium-bearing accessory minerals such as the apatite. According to apatite compositional variations and alteration geochemistry, these variations reveal the process of uranium dissolution, migration, and precipitation enrichment into ore bodies. Uranium was completely released during alkaline metasomatism, causing a sharp decline in U content from 53.1 ppm to 0.96 ppm. The formation of alkaline alteration fluids facilitates the extraction of uranium from the surrounding rocks (the Indosinian granite).

Analysis and countermeasures of asymmetric failure in layered surrounding rock tunnels based on FDEM: A case study

In recent years, deep tunnel projects in many regions of China have frequently encountered severe asymmetric failure issues in layered rock structures when crossing through such strata. The unpredictability of the direction and extent of these failures has posed significant challenges for subsequent support design. This paper investigates the asymmetric failure mechanisms of layered rock masses in the Hutou Beishan Mega Tunnel using the Finite-Discrete Element Method (FDEM). First, the smeared method within the FDEM framework is employed to analyze crack evolution, stress states, and asymmetric failure characteristics during tunnel excavation, with the simulation results being compared against field observations for validation. Subsequently, the effects of layer thickness, bedding angle, lateral pressure coefficient, and rock mechanical properties on the asymmetric failure of layered rock masses are systematically explored. The simulation results indicate that the bedding angle and lateral pressure coefficient are the primary factors contributing to the unpredictability of the direction and extent of asymmetric failure in layered rock masses. Based on the analysis of the failure characteristics of these rock masses, the study classifies asymmetric failure into three typical types, providing valuable reference points for predicting the zones and depths of concentrated damage after excavation and for optimizing tunnel support design.

A 4D Soil-Structure Interaction Model Testing Apparatus

Abstract A new three-axis loading frame has been developed to enable real-time visualization of in-situ soil and rock structure interactions via X-ray tomography during small-scale model testing. The constructed frame is capable of performing a wide range of small-scale 1g tests and can accommodate monotonic and cyclic actuation under both load and displacement control. The compact size of the system enables remote multi-axis operation from within an X-ray cone-beam scanning bay, a capability which is owed to a comprehensive design process. Design and fabrication involved a blend of physical and numerical experiments to assess suitable construction materials and performance. In this scope, the new equipment is discussed and its capability is showcased.

Time‐domain spectra of ultrasonic wave transmitted through granite and gypsum samples containing artificial defects

AbstractThe internal defects in rock masses can significantly impact the quality and safety of geotechnical projects. Mechanical waves, as a common nondestructive testing (NDT) method, can reflect the external and internal structures of rock or rock masses. Analyses on the reflected and transmitted waves enable nondestructive identification and assessment of potential defects within rocks. Previous studies mainly focused on the variation of single or limited wave features like main frequency, amplitude and energy between the intact and non‐intact samples. In fact, most information contained in the waveforms is neglected. Techniques of data mining can provide a powerful tool to reveal this information and therefore a more accurate determination of the internal structures. In this study, 995,412 NDT data from 14 types of granite and gypsum samples with different cross‐section shapes and different types of defects are recorded by an ultrasonic wave generation and collection system. This dataset can be used not only as the training data for defect classification in NDT but also as a good reference for conventional NDT analyses. Besides, time‐series data analysis is an opportunity and challenging issue, this dataset holds great potential for broader application in general time‐series classification analysis.

Investigation of Fatigue Mechanics and Crack Evolution Characteristics of Jointed Specimens Under Cyclic Uniaxial Compression

ABSTRACTNonpersistent joints are prevalent in engineering rock masses and are sensitive to cyclic loads induced by geological movements and engineering disturbances. Therefore, studying the fatigue mechanisms of rock masses with nonpersistent joints under cyclic compressive loads is crucial for ensuring the rational design and long‐term stability of rock engineering structures. Based on laboratory experiments, this study employed the discrete element method to create specimens with different nonpersistent joints, and uniaxial compressive cyclic loading tests were conducted on these specimens with different maximum cyclic stress levels. The results show that the joint inclination significantly affects the characteristics of jointed rock, such as deformation modulus, irreversible strain, energy evolution, and crack characteristics. Increasing the maximum stress in the stress path results in a rapid release of hysteretic energy in the jointed regions of the rock, which leads to an exponential decrease in fatigue life while an increase in initial irreversible strain, final irreversible strain, and hysteretic energy density. Additionally, the shear fracture zones on both sides of the model expand, and the propagation and merging of cracks between joints become more extensive and complex. The results are significant for studying rock fatigue instability and structure engineering design.

Exploring the axial performance of protective sheathed rock bolts through large-scale testing

Understanding the axial load transfer mechanism of rock bolts under diverse conditions is essential for optimizing reinforcement in rock structures, advancing our comprehension of rock support, and facilitating the design of robust engineering solutions. This paper reports the outcomes of an extensive experimental investigation, focusing on the axial behavior of protective sheathed rock bolts employed in corrosive environments, assessed through pullout tests. Three distinct testing setups were designed to evaluate comprehensively the performance of these rock bolts in various scenarios. The results indicated that the failure characteristics and axial behaviors of sheathed rock bolts differ significantly from conventional counterparts. The findings revealed two primary failure modes in sheathed rock bolts: bolt rupture and slip at the grout-sheath interface, based on the testing arrangement and encapsulation length. The lack of adhesion and interlocking at the grout-sheath interface prevents shear stress at the bolt-grout interface from reaching its maximum potential strength, resulting in grout damage manifesting as circumferential cracks. This, in turn, initiates crack formation, reducing the system’s bond strength. Additionally, it causes slip at the grout-sheath interface to occur at lower pullout loads. It can be inferred that the inner surface of the plastic sheath lacks the necessary structural integrity to withstand high loads, significantly impacting bond stress distribution and failure modes. The results demonstrate that the protective sheath remains intact up to an axial displacement of 28 mm, irrespective of the testing configuration. Additionally, it was observed that the maximum bond stress at the bolt-grout interface falls within the range of 6–8.7 MPa, which is below the shear strength of the grout. Consequently, achieving failure at the bolt-grout interface is not feasible.

Identification of Paleovolcanic Centers in the Bima District, East Sumbawa Island (Indonesia) as Guidance for Future Exploration of Cu-Au Deposits

The formation of Cu-Au mineralization, such as porphyry and epithermal deposits, is strongly associated with volcanic processes in specific tectonic settings, such as subduction zones. The identification of the presence of ancient volcanoes is one of the important steps to finding mineral deposits. This study aims to identify the presence of ancient volcanoes in the Bima District, eastern part of Sumbawa Island, as a step toward determining the potential indication of Cu-Au mineralization. The methods used in this research consist of a literature study, image analysis and remote sensing, field survey and data collection, and petrographic analysis. Image analysis using DEMNAS (Digital Elevation Model), including texture and pattern analysis using the concept of volcanic anatomy, aims to identify the remaining forms of ancient volcanoes. Field surveys and data collection include volcano geomorphology, lithology and sampling, and also geological structures. Petrographic analysis is conducted to qualitatively characterize the texture, structure, and mineralogy of volcanic rocks. The identification results show that there are at least ten volcanoes (crown) identified through image analysis, namely Doro Mbangga, Doro Baku, Doro Donggo Masa, Doro Rompo, Doro Sape, Doro Kowo, Doro Jia, Doro Sambori, Doro Mangge, and Doro Lambu. Each of these volcanoes has one or more eruption center (hummock). The eruption center identified in the central, proximal, to distal facies of the volcano, even superimposing one volcano product with another, and spread around 80-90% in the study area. The volcanic facies in the study area are characterized by the central part being composed of lithologies such as intrusive rocks, lava, and diatreme breccia, while the proximal and distal facies are composed of breccia, volcanic breccia, and tuff. Hydrothermal alteration zones are identified in the central and proximal facies of the volcano. These alterations were associated with the presence of eruption centers, where the abundance of eruption centers means that hydrothermal alterations are particularly well developed and pervasively formed. Identified argillic and advanced argillic alteration associated with stockworks forming a lithocap environment. In addition, the presence of intrusive rocks such as diorite and dacite with chloritic and sericitic alteration in the central facies of Doro Baku can be associated with the presence of deposits such as porphyry and epithermal, so the identification of ancient volcanic eruption centers in the Bima district has implications for the potential discovery of Cu-Au mineralization, such as porphyry and epithermal deposits.

Study on the pore structure and permeability evolution of tight sandstone under liquid nitrogen freezing‐thawing cycles based on NMR technology

To further raise the gas extraction efficiency of the tight sandstone, the liquid nitrogen (LN2) freezing-thawing cycles method can be employed to improve the permeability of the low-permeability reservoirs. Permeability is generally regarded as a macroscopic description of the pore structure and usually has functional relationship to pore structure properties. The permeability of the rock is closely related to the change of microscopic pore structure. The permeability of rock depends on how the subzero temperatures changed the microscopic pore structure of rock, but it has not yet been confirmed obviously. In this study, the nuclear magnetic resonance (NMR) technique was adopted to investigate the pore structure evolution law and permeability of the tight sandstone with different LN2 freezing-thawing cycles. The results demonstrate that the LN2 freezing-thawing cycles promotes pore development and micro-fracture connection, and enhances the pore connectivity. The proportion of meso-pores, macro-pores and micro-fractures in the sandstone samples increases significantly, which provides a channel for the sandstone gas flow and extraction. Total porosity and effective porosity of the samples present a trend of rapid increase as the number of LN2 freezing-thawing cycles increasing, while the residual porosity decreases as the number of LN2 freezing-thawing cycles increasing. Coates model, SDR model (mean T2 model) and PP model were used to calculate and evaluate the permeability of the samples subjected to different LN2 freezing-thawing cycles. Furthermore, PP model can provide a better permeability estimate than the classical Coates and SDR model.

Investigation on Asymmetric Dynamic Response Characteristics of Anchored Surrounding Rock under Blasting Excavation of Inclined Layered Rock Tunnel

The dynamic response stability analysis of the anchored surrounding rock during blasting construction is crucial to ensure the safety of construction. Taking the Wuwan Tunnel in Luoyang as the engineering background, combined with methods such as physical simulation experiments, numerical simulation experiments, and on-site experiments, the asymmetric effects of layered rock mass on the surrounding rock and support structure during blasting excavation were studied. The asymmetric effects of tunnel blasting excavation on the surrounding rock and support system under the condition of a bedding angle of 30° were analyzed and summarized. The results indicate that when the blasting stress wave passes through the bedding plane, the stress wave will undergo significant attenuation. The strain generated by the anchor rod passing through the bedding plane exhibits asymmetry due to the reflection and weakening of the blasting stress wave after passing through the bedding plane.

Effect of Primary/Artificial Interface on Dynamic Failure Behavior of Combined Coal and Rock: Monitoring by High-Speed Imaging and Scanning Electron Microscopy.

The instability of the primary coal and rock structure significantly impacts the safety of coal mining and construction. The complex coal-rock interface cannot be simplified as a smooth surface. To investigate the dynamic response of primary composite coal and rock (primary-CCR), we studied the impact of load, hydrostatic pressure, and interface type on the mechanical behavior and macro/micro failure characteristics using a separate Hopkinson bar, a high-speed camera, and a scanning electron microscope. The results indicate a linear relationship between the composite strength, impact toughness, and impact velocity of the two types of composite coal and rock. The mechanical behavior of the primary-CCR initially increases and then decreases with the rise of hydrostatic pressure (turning point: 10 MPa). There is a positive correlation between artificial combined coal-rock (artificial-CCR) and hydrostatic pressure. The dissipative energy of combined coal and rock increases linearly with impact velocity. Initially, the dissipative energy per unit fracture area increases with hydrostatic pressure, then decreases as pressure continues to rise. Additionally, an increase in impact load causes the energy dissipation inflection point to shift forward. The primary interface significantly reduces the energy threshold for instability failure, resulting in a transition from energy transfer to energy dissipation in rock components. This transition manifests as the failure of artificial combined coal and rock cracks, which develop into rock fragments at an impact velocity of 14 m/s. Furthermore, the change in section roughness of coal and rock correlates with the degree of macroscopic crack growth, following the order: coal > primary-CCR > artificial-CCR > rock.

Research on compression failure criteria and characteristics of rock-concrete assemblies with rough interfaces

The combination of rock and concrete lining structures is a typical composite structure in the field of engineering. This study is based on the concept of equivalent strain energy and establishes a mechanical equivalent model for rock-concrete assemblies (RCA). Assuming that both rock and concrete satisfy the Mohr-Coulomb criterion, we derive the shear failure criterion of the equivalent model considering the roughness of the rock-concrete interface. The applicability of the model was verified through uniaxial and triaxial tests on eight different types of RCA structures. The research results indicate that an increase in confining pressure enhances the strength of the RCA. When the confining pressure reaches a certain value, concrete only experiences shear failure, and no macroscopic cracks appear in the rock. The structure of the RCA tends towards isotropy. As the height ratio of the RCA increases, its strength decreases. At minimal concrete height ratios, the strength of the RCA gradually approaches that of concrete. This study can provide valuable insights for designing and evaluating stability in engineering rock bodies within diverse geological environments.

Exploring the Impact of Mineralogy on Pore Structure and Fluid Dynamics in Tight Reservoir Rocks: Insights for Enhanced Oil Recovery and Gas Storage

Exploring the Impact of Mineralogy on Pore Structure and Fluid Dynamics in Tight Reservoir Rocks: Insights for Enhanced Oil Recovery and Gas Storage