Rock Parameters Research Articles (Page 6)

Aiming at the shortcomings of the BP neural network in practical applications, such as easy to fall into local extremum and slow convergence speed, we optimized the initial weights and thresholds of the BP neural network using the particle swarm optimization (PSO). Additionally, cloud computing service, web technology, cloud database and numerical simulation were integrated to construct an intelligent feedback analysis cloud program for underground engineering safety monitoring based on the PSO-BP algorithm. The program could conveniently, quickly, and intelligently carry out numerical analysis of underground engineering and dynamic feedback analysis of surrounding rock parameters. The program was applied to the cloud inversion analysis of the surrounding rock parameters for the underground powerhouse of the Shuangjiangkou Hydropower Station. The calculated displacement simulated with the back-analyzed parameters matches the measured displacement very well. The posterior variance evaluation shows that the posterior error ratio is 0.045 and the small error probability is 0.999. The evaluation results indicate that the intelligent feedback analysis cloud program has high accuracy and can be applied to engineering practice.

The potential of unconventional hydrocarbon resources has been unlocked since the hydraulic fracturing technique in combination with long horizontal wells was applied to develop this type of reservoir economically. The design and optimization of the fracturing treatment and the stimulated reservoir volume and the forecasting of production performance are crucial for the development and management of such resources. However, the production performance of tight gas reservoirs is a complicated nonlinear problem, described by many parameters loaded with uncertainty. The complexity of the problem influences and inspires the sophistication of the solution to be used. This paper proposed an artificial network model that allows for fast, extended, and accurate analyses of the production performance of multiple fractured unconventional tight gas wells. In the comprehensive approach developed, the reservoir rock parameters, the drainage area, and the hydraulic fracture parameters are treated as a variable input to the model. The analysis is no longer constrained by fixed “shoes box” geometry, and the values of the parameters defining the reservoir and stimulated volume are not limited to a few discrete values. The numerical experiment used to construct a database for model development was designed using a genetically optimized Latin hypercube sampling technique. A special approach was used in the preparation of “blind data”, which are crucial for truly reliable model verification. In the result, a developed tool offers an extended rock-fluid description, flexible model, and stimulated reservoir volume dimensioning and parameterization, as well as a high degree of applicability in sensitivity analysis and/or optimization.

Geophysical research methods are actively used in the exploration of hydrocarbon deposits, the peculiarity of which is the remoteness of the studied objects from the observer's point. The main purpose of geophysical research is to obtain, transmit, and process information about the topography, soil composition, and quantity and location of groundwater. Such studies are carried out at the end of drilling the well of the exact cut interval using devices lowered into the well on a special geophysical cable. Currently, equipment is being actively developed that helps geophysicists determine the parameters of rocks during the drilling of a well. The signals received in the wells are transmitted to the surface using special built-in transducers on the drill pipe column via a cable built into the column. The development of new, innovative, modern devices for geophysical research is characterized by the complication of equipment with the expansion of parameters, tasks for performing a complex of geophysical research. A number of upgrades to the pulsed neutron gamma-spectrometric logging equipment, which will be able to bring the existing domestic equipment to the level of the latest Western analogues. The scheme of the pulsed gamma neutron device with the T100 calibrator is unique in the industry. This scheme allows for multipoint calibration of sensitivity to oil and gas, calibrated logging performance in accordance with factory specifications and consistency of measurements between tools, regardless of the age of the tool or the conditions of well operation.

This study aims to correlate the mechanical properties measured in the laboratory and the field for weak and crushable limestone in a mining site containing random karstic cavities. Compressive tests were performed in the laboratory to obtain Unconfined Compressive Strength (UCS) and rock mass modulus (Erm). Field tests were: i) boring and drilling cores that allowed obtaining Rock Quantification Distribution (RQD) and recovery rock parameter (REC), and ii) Ground Penetration Radar (GPR) to detect and locate random cavities in the underground limestone deposit. The correlation between the Em/UCS rate and the RQD was determined and analyzed. Based on the role of the new interpretation of the Geological Strength Index (GSI) and its relationship with the Erm/UCS rate, a mathematical relationship was determined to link GSI and RQD. This relationship was a basis for modifying the generalized Hoek-Brown criterion, involving the amplitude of reflected electromagnetic waves (EM) provided by GPR field tests.

The use of geothermal energy is spreading globally due to its many advantages, especially for heating and cooling. The correct design of a geothermal system requires knowledge of the parameters of the subsoil rocks, and particularly the thermal conductivity (k), which is the intrinsic ability of a material to transfer thermal energy as a result of a temperature gradient. A thermal conductivity map of the geological formations is time-consuming to produce, but can be of great help when selecting the location of a low-enthalpy geothermal installation, resulting in significant savings and an increase in the efficiency of that installation. The preferred option for determining k is an in situ thermal response test, but laboratory methods may be an alternative if it is not available or affordable. In this work, the needle thermal probe method has been used to measure the k of representative outcropping rocks in Oviedo (NW Spain), since it allows to obtain a rapid determination, its cost is comparatively low and it can be implemented in a portable device. 162 measurements have been carried out on a total of 27 samples, ranging from 0.2 (clay) to 5.4 W m−1 K−1 (quartzite). A relationship has been found between the k of the rocks and their characteristics, such as mineralogy, anisotropy or geological age and a thermal conductivity map was created.

Abstract This paper aims at deriving a closed‐form solution for deep lined tunnels within a saturated anisotropic poro‐elastic medium. The derivation of the solution is carried out with the assumption of plane strain conditions along the tunnel axis, an isotropic elastic liner, a steady‐state flow, and perfect contact between the liner and rock. For this purpose, the complex potential function approach pioneered by Lekhnitskii for the anisotropic elastic body was used to develop the mechanical response of the rock mass. A complex hydraulic potential function is also introduced to solve the steady state fluid flow. Then the well‐known Biot theory is chosen to describe the hydro‐mechanical coupling of the anisotropic saturated rock. The stress and displacement solutions of both the liner and the surrounding rock, considering the tunnel face advance with respect to the considered section, are derived based on the principle of the convergence‐confining method. Comparisons with previous closed‐form solutions for isotropic case and finite element solution for anisotropic case were made to show the accuracy of the current closed form solution. Sensitivity analysis is performed based on this analytical solution to highlight the effect of some rock parameters on the stress and displacement of the liner.

As a basic parameter of rock, the rock bridge angle plays an important role in maintaining the stability of rock masses. To study the size effect of rock bridge angle on the uniaxial compressive strength of rocks, this paper adopts the principle of regression analysis and combines numerical simulation to carry out relevant research. The research results indicate that: (1) the uniaxial compressive strength decreases with the increase of the rock bridge angle, showing a power function relationship; (2) The uniaxial compressive strength decreases with the increase of rock size and tends to stabilize when the rock size is greater than 350 mm, showing a significant size effect. (3) The fluctuation coefficient of compressive strength increases with the increase of rock bridge angle and decreases with the increase of rock size; When the rock size is 350 mm, the fluctuation coefficient is less than 5%; (4) The characteristic compressive strength and characteristic size both increase with the increase of the rock bridge angle.

Discrete Element Method (DEM) has been successfully utilized to model rock behavior based on particle flow code (PFC), which is extensively employed in solving various problems related to rock engineering and geomechanics. Therefore, a convenient method for selecting appropriate microparameters of PFC for model generation is necessary. The present study aims to develop a novel approach that calculates proper micro-strength parameters for the contact bond model (CBM). Firstly, based on Plackett–Burman (PB) design, qualitative research is conducted and it is found that the main factors that influence the Brazilian tensile strength is microscopic tensile strength. We analyzed the stress conditions of a Brazilian disc’s vertical diameter using both continuum models and DEM. From this analysis, we establish a theoretical relationship between rock tensile strength and micro-strength parameters. Subsequently, a large number of numerical Brazilian tests were conducted to obtain the statistical relationship between the geometric parameters of balls, micro-strength parameters and the Brazilian tension strength. The results of the numerical simulation were then used to refine the theoretical equation mentioned above, resulting in a modified equation for rock tensile strength and micro-strength parameters. Finally, after verification, we confirm the feasibility of the method in this paper.

In landslide control engineering, anti-slip piles are the most commonly used means. This article established a numerical model of the interaction between fully weathered granite landslides and anti-slip piles based on the strength reduction method. Firstly, five pile-soil interaction models with different pile spacing were established using Abaqus software, and individual components were generated and assembled using the stretching function. The friction surface is used between the pile and soil, and the normal and tangential contact characteristics are both Penalties. Secondly, the strength reduction method based on displacement criteria is used to reduce the rock and soil parameters to the unstable stage before failure, while calculating the slope safety factor. Then, the influence of anti-slip pile spacing on slope stability, pile shear force, bending moment, and soil arch effect are studied. The strength reduction method and pile-soil interaction model used in this article can effectively avoid single pile effects and have high accuracy in characterizing soil arching effects. The results afford certain application and promotion values by providing theoretical references and technical guidance for similar anti-slide pile reinforced slope projects.

The fracture parameters of rocks, including fracture toughness and fracture energy, represent their resistance to crack propagation under external stress. These parameters play a critical role in engineering design, construction safety, geological mechanics research, and rock material assessment. This study determined the fracture parameters of granite under Mode I loading conditions using notched semicircular bend (NSCB) and single-edge notched beam (SENB) specimens. Although there was little difference between the initial and unstable fracture toughness values of the two specimen configurations, significant differences were observed in the fracture process and other fracture parameters. For example, the NSCB specimen exhibits a higher elastic modulus, and it witnessed rapid failure after reaching the peak load, whereas the SENB specimen displayed a more gradual failure process with a distinct post-peak stage. This may be one of the reasons for the higher fracture energy in the NSCB specimen than in the SENB specimen. Based on finite element analysis and the extraction of the tangential stress at the crack tip region, the application of the maximum tangential stress fracture criterion provided a robust explanation for the coherence observed in the unstable fracture toughness test results between the two specimen configurations.

The article presents results of the research on forecasting the risks of underground roadway stability loss based on the results of mine monitoring. The method is used for safety control in the process of conducting mining operations and re-exploitation of roadways as industrial facilities. The risk assessment was carried out with allowance for spread of physical and mechanical parameters of rocks; this approach is confirmed by procession of data of more than 1000 experiments. Mining-and-technical factors and their negative impact on the rock destruction were identified and systematized. The structure of risk control in a geotechnical system “rock massif - roadway” was substantiated. The method for forecasting the risks of underground roadway destruction based on the results of the mine research was further developed. The method differs from the well-known ones by taking into account the dominant influencing factors, variations of values and standard deviations of the forecasted risks of roadway functionality loss and criteria for violation of its technological air gaps at a certain point in time. This makes it possible to assess the degree of danger of mine roadway stability loss and to undertake response measures more reasonably.

Detection methods for strength deterioration and structural characteristics of fractured rock based on digital drilling

To estimate catchment-scale hydrogeological parameters such as hydraulic conductivity (k) and specific yield (Sy), the streamflow recession analysis method proposed by Brutsaert and Nieber (1977) was used. The analysis employed the technique of fitting a theoretical recession curve to the observed data in which three points of transition between the short- and long-term flow regimes were determined. This method is a simple, fast, and cheap alternative to standard point-based hydrogeological methods using investigations carried out in hydrogeological boreholes. The study area covered the mountainous catchment of the Biała Lądecka River, located in south-western Poland and composed of metamorphic rocks. The hydrogeological environments drained by the Biała Lądecka are two zones, i.e. the zone of weathered covers and rock debris and the zone of fractured rock mass. The k values determined based on the recession analysis were in the boundary zone of the range from 10−4 to 10−5 m/s and they represented the upper range of the values reported in the literature (from 10−4 to 10−7 m/s). The Sy values at a level of 0.38–1.02%, in turn, entirely fitted the literature data. The results confirm the thesis that the recession method, despite certain limitations in terms of its applicability, can be well adapted to the conditions of a mountainous catchment composed of crystalline rocks where a cool temperate climate prevails.

The uncertainty of surrounding rock parameters varies due to changes in the boundary conditions of the tunnel model, and no suitable method to ensure that the updated parameters of the finite element model (FEM) are applicable throughout the constructional environment. To address this issue, a probabilistic baseline model method was introduced to invert the rock parameters and obtain values suitable for the complete constructional environment. First, the probabilistic statistical theory was applied to statistically analyze the measurement data from tunnels under different constructional environments, which provides insight into the variation in rock parameters. Then, an objective optimization function based on a genetic algorithm (GA) was constructed to optimize the accuracy by minimizing the error between the measurement data and the simulation data. Next, a Kriging model was built that utilized Young’s modulus and cohesion as updated parameters. This approach contributes to overcoming the inefficiency of multi-objective optimization computations. By using the Kriging model, optimal values for the rock parameters were obtained. Finally, the effectiveness and applicability of the proposed method were validated by comparing the measured data with the updated model data under different constructional environments.

The aim of this study was to explore the mapping relationship between the temperature and the dielectric parameters of coal and rock under variable temperatures as well as to determine the characteristics of a dielectric anomaly response. Experiments were performed using lignite, nonstick coal, gas coal, coking coal, and anthracite. The evolution of pyrolysis characteristics, microcrystal structure, and dielectric properties with changing temperature was investigated, and the changes in the dielectric parameters of coal and rock were comprehensively analyzed. As such, the cause of the dielectric anomaly with changing temperatures of coal and rock was revealed. The results show that the dielectric properties of coal at different pyrolysis temperatures are closely related to the degree of intermolecular thermal motion, the evolution of microcrystal structure, and the mechanism of polarization response. In the low-temperature stage, the thermal motion of coal molecules is weak and exhibits electronic polarization, and the dielectric parameters change slightly with temperature while being dependent on the moisture content. In the high-temperature pyrolysis stage, the intense molecular thermal motion leads to the breaking of chemical bonds and the release of volatiles; moreover, the distance between aromatic layers of coal decreases, the order of aromatic structure increases, the dipole turning polarization is the main polarization type, and the dielectric response is obvious. When the pyrolysis reaction is basically complete, the dielectric constants of the five coal samples reach the maximum. As the temperature increases continuously, the coal structure is destroyed by the weakening of the thermal motion of the coal molecules and the accumulation of thermal stress; meanwhile, the dielectric constant decreases gradually, while the dielectric loss and tangent of dielectric loss increase rapidly. At the same temperature, the dielectric constant decreases with an increase in test frequency. These results lay a foundation for the inversion of dielectric data in fire areas of coal mines.

Failure precursors recognition method for loading coal and rock using the fracture texture features of infrared thermal images

Laser drilling through Hashma sandstone

The Mallina Basin in Western Australia, situated in the central part of the Pilbara Craton which is one of the world's oldest cratons, is a structurally deposited basin subjected to multiple episodes of deformation and magmatic intrusion. The Calvert gold deposit in Mallina Basin is heavily covered by Quaternary, thus, it is hardly to identify any distinct mineralization indicators, and there is no any significant progress in exploration so far. The SQ-3C dual frequency induced polarization facility that is developed by China is introduced to carry out the dual frequency IP survey, the author’s team have tested all the types of different rock samples to collect the geophysical parameters in the Calvert area, and the selection of suitable facility and working frequency is based on the geological characters of the Calvert deposit and the geophysical parameters of rocks, and some processes are undertaken to weaken the interference triggered by the electromagnetic coupling, and an IP anomaly zone was delineated. Through the drilling program in the IP anomaly zone, a gold ore body that has the same orientation with the IP anomaly zone was controlled; this result demonstrated the dual frequency IP survey is effective in the local area and provide an efficient technical method for the mineralization prospecting, and this geophysical survey project sets an example for the familiar type of gold deposit in the local area.

Theoretical analysis and numerical simulation analysis of energy distribution characteristics of surrounding rocks of roadways

Energy, gases, and solids in underground sites are stored in mining excavations, natural caverns, salt caverns, and in the pore spaces of rock formations. Aquifer formations are mainly isolated aquifers with significant spreading, permeability, and thickness, possessing highly mineralized non-potable waters. This study discusses the most important aspects that determine the storage of natural gas, hydrogen, or carbon dioxide in deep aquifers. In particular, the selection and characterization of the structure chosen for underground storage, the storage capacity, and the safety of the process are considered. The choice of underground sites is made on the basis of the following factors and criteria: geological, technical, economic, environmental, social, political, or administrative–legal. The geological and dynamic model of the storage site is then drawn based on the characteristics of the structure. Another important factor in choosing a structure for the storage of natural gas, hydrogen, or carbon dioxide is its capacity. In addition to the type and dimensions of the structure and the petrophysical parameters of the reservoir rock, the storage capacity is influenced by the properties of the stored gases and the operating parameters of the storage facility. Underground gas storage is a process fraught with natural and technical hazards. Therefore, the geological integrity of the structure under consideration should be documented and verified. This article also presents an analysis of the location and the basic parameters of gas storage and carbon dioxide storage facilities currently operating in underground aquifers. To date, there have been no successful attempts to store hydrogen under analogous conditions. This is mainly due to the parameters of this gas, which are associated with high requirements for its storage.