Mechanical Properties Of Granite Research Articles

Laboratory investigation on physical and mechanical behaviors of granite after heating and different cooling rates

As an important formation of geothermal reservoirs, granite has very complex microstructure and strong heterogeneity which play an important role in the damage and failure mechanical behavior of granite under different temperatures and cooling rates. In order to better understand the influence of microstructure on the multiscale physical and mechanical properties of granite at evaluated temperatures and cooling rates, this paper conducted a series of macroscopic and microscopic experimental investigations on the granite samples after a heating with two cooling rates treatment. The results show that the failure mode changes from brittle to ductile at 400 °C which is the critical temperature for both macroscopic and microscopic properties. The physical and mechanical properties of specimen after air cooling treatment increase at 200 °C due to the transition of macropores into micropores. Transgranular cracks take place in feldspar at 400 °C and numbers of intergranular cracks develop inside all minerals at 500 °C. The number and width of microcracks in water-cooled samples are much greater than those of air-cooled simples. Based on these experimental investigations, a cross-scale characterization method of Young’s modulus is proposed by introducing a thermal damage factor into the Mori–Tanaka method to consider the thermal damage induced by the thermal treatment.

Study on the Degradation Law of Physical and Mechanical Properties of Granite under the Action of Freeze-thaw Cycle

This study demonstrates the effect on the mechanical properties of granite through the freeze-thaw cycle test method, and investigates the mechanical property parameters and its changing law of the rock samples under different numbers of freeze-thaw cycles. The results show that with the increase of the number of freeze-thaw cycles, the physical property parameters such as mass and longitudinal wave speed of the samples show a tendency of attenuation. Mechanical property parameters such as peak strength and elastic modulus of the specimen also showed a trend of decay.

Evaluation of Damage Stress Thresholds and Mechanical Properties of Granite: New Insights from Digital Image Correlation and GB-FDEM

Evaluation of Damage Stress Thresholds and Mechanical Properties of Granite: New Insights from Digital Image Correlation and GB-FDEM

Analysis of physical and mechanical properties of granite under different cooling methods under high-temperatures thermal cycles

This study explores the impact of external pressure and high-temperature erosion on the physical and mechanical properties of granite, the geothermal well storage medium, during geothermal exploitation. Objectives include evaluating the effects of repeated heating and cooling cycles at different temperatures on porosity, permeability and mechanical performance, with a focus on confining pressure's influence on permeability. The results indicate that under water-cooling and ambient conditions, porosity and permeability increase with cycle repetition, whereas compressive strength and elastic modulus decrease. Notably, Group B's (water-cooled) mechanical performance surpasses that of Group A (room temperature cooling) when porosity is below 1.5%. However, with increasing porosity owing to thermal cycling, Group B's granite becomes inferior to that of Group A. Micro-computed tomography scans reveal a post-cycling granite pore structure dominated by horizontal cracks, with primary uniaxial compression damage in the vertical direction. Thermal cycling reduces crack paths and load-bearing capacity, diminishing granite's mechanical performance. This study offers insights into subtle interactions between cooling methods and porosity during geothermal energy exploitation. It provides valuable guidance for optimizing geothermal energy use and mitigating potential adverse impacts on rock integrity, laying a foundation for further research and practical applications in geothermal energy exploitation.

Experimental Study on the Influence of Real-Time Temperature Cycling on Physical and Mechanical Properties of Granite

In this paper, a self-developed multi-functional high-temperature rock triaxial servo control testing machine was used to carry out uniaxial compression tests on the granite after the cooling and heating cycles under real-time temperature. The physical and mechanical properties of two types of granite damaged by hot and cold cycling under real-time temperature were discussed, and the changes in apparent color, longitudinal wave velocity, elastic modulus, uniaxial compressive strength, and damage characteristics of the specimen were revealed. The research results show the following: (1) With the increase in temperature or the increase in number of cycles, the uniaxial compressive strength, longitudinal wave velocity, and elastic modulus of the samples under the two cooling methods all show a decreasing trend, but the decrease in the range is different. The change range of the sample with temperature is greater than that with the number of cycles. (2) Under the dual action of real-time temperature and cold heat cycle damage, the failure form of granite is very random, but it is mainly shear failure, longitudinal splitting failure, and conical failure, and it is accompanied by a high temperature with the increase in the number of cycles, and the degree of crushing of the test piece gradually increases. For example, the sample under 600 °C water cooling for 25 cycles is crushed and destroyed. (3) As the temperature and the number of cycles increase, the surface of the water-cooled sample becomes rougher with the increase in the temperature and the number of cycles and the higher temperature, along with more cracks and debris; the increase in the temperature cycle, no obvious cracks appeared on the surface. The test results in this paper can provide relevant theoretical guidance for the stability and safety of rock in geothermal mining.

Influence of different cooling treatments on the mechanical properties of granite under Brazilian splitting test by grain‐based model 3D

AbstractDuring the operation of an enhanced geothermal system (EGS), the reservoir rock undergoes different cooling treatments based on the distance to the surface rock. The tensile capacity of reservoir rocks is a key parameter in estimating the parameters of the hydraulic fracturing process. Therefore, the gain‐based model 3D (GBM3D) was constructed to explore the micro behavior of granite under the heating/cooling process and the Brazilian splitting test. The numerical results demonstrate the ability of GBM3D to reproduce the grain interlocking and rotational resistance behavior, making it applicable to simulate the mechanical behavior of granite under uniaxial compression and the Brazilian splitting test. Temperature and cooling rates have significant effects on the stress‐strain curves. With the increase in temperature, the curves after peak strength translate from brittle to ductile, and the turning point of water‐cooled granite is lower than that of air‐cooled granite. When more flaws are present in the specimen, micro‐cracks tend to occur along the loading axial near the center of the specimen. This result can be used to explain the defect in numerical simulation, where cracks are easy to develop near the loading position under the Brazilian splitting test. This work can provide recommendations for hydraulic fracturing.

Structural properties and failure characteristics of granite after thermal treatment and water cooling

In a variety of fields such as exploitation of geothermal energy and the reconstruction of nuclear waste storage, both of high-temperature and cooling process change the physical and mechanical properties of granite. Uniaxial compression tests were performed on five groups of granite samples at 25 °C, 200 °C, 400 °C, 600 °C and 800 °C after water cooling, and CT scanning, acoustic emission(AE) monitoring and X-ray diffraction(XRD) scanning were used to investigate the structure properties and failure characteristics of granite. It is found that the proportions of pore volume greater than 106 μm3 and less than 105 μm3 with are positively and negatively correlated with the thermal treatment temperature respectively. The mechanical properties of granite are significantly deteriorated by temperature gradient shock, and crack development scale during failure process overall increases as implied by AE response. The failure intensity index η is proposed to characterize the failure severity of granite, and the value of η descends with the increase of thermal treatment temperature, indicating the failure severity of granite is alleviated. Three types of loading failure mode are classified for water-cooled high-temperature granite. The failure mode of granite at 200 °C and 600 °C is tensile failure and tensile-shear failure respectively, while the granite samples are dominated by shear failure at 25 °C, 400 °C and 800 °C.

Shaping characteristics of excavation contours in sequential controlled fracture blasting of rock-anchored beams in Shuangjiangkou underground powerhouse

Influences of high in-situ stress generally need to be considered when excavating deep underground caverns. The dynamic fracture behaviors of rocks under blast loads were investigated by using the rock-anchored beam excavation in underground powerhouses of Shuangjiangkou Hydropower Station in Sichuan Province, China as the engineering background. To solve the problems of the poor blasting breakage effect of rocks and the difficulty in protecting surrounding rocks during excavation, mechanical properties of granite under static and dynamic loads were investigated and the sequential controlled fracture blasting (SCFB) method was adopted during in-situ tests. Based on the Riedel-Hiermaier-Thoma constitutive model and the strength criterion, software LS-DYNA was employed to simulate the dynamic propagation of blasting-induced cracks. The contour shaping effect obtained via numerical simulation is generally consistent with the test results. The results show that SCFB can to some extent control the direction of crack initiation and rock fracture behavior of the blasthole wall cracks and the spacing of successive bursting holes is about 10 times the diameter of the blastholes when the cracks between the blastholes are shaped the best effect. Moreover, the magnitude and direction of principal in-situ stress can both affect the propagation path and length of blasting-induced cracks. The results of the research on the excavation and construction of deeply buried underground caverns have a certain reference value.

Evolution of Physical and Mechanical Properties of Granite after Thermal Treatment under Cyclic Uniaxial Compression

The combined effects of thermal and cyclic loading result in complex mechanical behavior in engineering rock masses. The study of the physical and mechanical properties of these rock masses is of great importance for improving the stability and sustainability of structures built on thermally treated rock masses. In order to understand the failure mechanism, uniaxial compression tests and cyclic loading and unloading tests were conducted on granite specimens that had undergone thermal treatment at various temperatures. The test results indicate that the density and P-wave velocity of the specimens decrease while the degree of damage increases after thermal treatment. The compressive strength and elastic modulus of the specimens generally decrease as a result of thermal treatment, although thermal hardening does occur within the temperature range of 200–400 °C. The dilatancy characteristics of the specimens change with the treatment temperature, and they are more prone to shear dilation under external loading. Furthermore, the failure mode of the specimens transitions from brittle to ductile failure as the treatment temperature increases. The combination of thermal treatment and cyclic loading causes the rock fragments to become looser and finer following specimen failure.

Correlations between mineral composition and mechanical properties of granite using digital image processing and discrete element method

This study investigated the correlations between mechanical properties and mineralogy of granite using the digital image processing (DIP) and discrete element method (DEM). The results showed that the X-ray diffraction (XRD)-based DIP method effectively analyzed the mineral composition contents and spatial distributions of granite. During the particle flow code (PFC2D) model calibration phase, the numerical simulation exhibited that the uniaxial compressive strength (UCS) value, elastic modulus (E), and failure pattern of the granite specimen in the UCS test were comparable to the experiment. By establishing 351 sets of numerical models and exploring the impacts of mineral composition on the mechanical properties of granite, it indicated that there was no negative correlation between quartz and feldspar for UCS, tensile strength (σt), and E. In contrast, mica had a significant negative correlation for UCS, σt, and E. The presence of quartz increased the brittleness of granite, whereas the presence of mica and feldspar increased its ductility in UCS and direct tensile strength (DTS) tests. Varying contents of major mineral compositions in granite showed minor influence on the number of cracks in both UCS and DTS tests.

Influence of hole diameter on mechanical properties and stability of granite rock surrounding tunnels

Nowadays, the development and utilization of more and more engineering construction are closely related to granite. However, many granite rock masses in Qingdao contain natural hole defects, which have a great impact on the mechanical properties of granite. It may even cause instability of surrounding rock and safety accidents. Therefore, in this paper, we discuss the influence of the hole diameter on the mechanical properties and stability of granite rock surrounding tunnels. Uniaxial compression experiments were conducted on granite with different hole diameters, and monitoring was carried out using the acoustic emission system and the XTDIC (Xintuo 3D Digital Image Correlation) three-dimensional–full-field strain-measurement systems. The relationship between the strength, deformation, and hole size of granite was investigated. In addition, using the Yangkou tunnel as the prototype and the PFC2D (Particle Flow Code of 2D) particle-flow–numerical-simulation program, a working tunnel model with different hole sizes was established to simulate the influence of natural hole defect sizes on the stability of rock. The results show that: (1) with an increase in hole diameter, the uniaxial compressive strength and elastic modulus of the granite sample gradually decreased. The brittleness of the granite samples gradually decreased, and the ductility gradually increased. (2) Under the action of axial stress and with an increase in the hole diameter, the sample was more likely to produce a stress concentration around the hole defect, which increased the deformation localization band, development, and expansion, as well as the intersection degree. As a result, granite samples are more likely to develop new cracks. These cracks increase in number and size, reducing the compressive strength of the granite sample. (3) The size of the hole defects significantly affected the damage and mechanical properties of the model surrounding rock. When increasing the hole diameter, the defect area increased and the tensile stress concentration near the hole in the localized rock became more evident. In addition, the stability of the rock surrounding the tunnel was significantly reduced, and its bearing capacity was weakened, leading to easier crack initiation and rock damage.

Mechanical properties of granite at high temperature subjected to true triaxial compression

Mechanical properties of granite at high temperature subjected to true triaxial compression

Mechanical Properties of Granite / Pulverized Coconut Shell Particulate Hybrid Reinforced Epoxy Composites

Mechanical properties of particulate granite and pulverized coconut shell hybrid reinforced epoxy composites were studied in this research, with the aim of converting agro-waste and natural occurring element to develop a new composite material for engineering applications. The stir cast method was used to produce the composites. The hybrid composites were developed by adding varying weight percentage of fine granite/coconut shell particles as reinforcement to epoxy matrix and the effect of the particles on the mechanical properties of the composite produced was investigated. The result revealed that the tensile strength ranges between 14.44 – 22.78 MPa, tensile modulus ranges between 300.52 – 718.47 MPa, flexural strength and flexural modulus varies between 43.03 – 77.19 MPa and 1009.35 – 1820.81 MPa, respectively; impact strength varies between 33 – 54 Joules and the hardness varies between 30.14 – 46.14 HRC. Finally, from the investigation, it is evident that the selection of percentage of filler content suitable for the polymer composite depends on the required properties for various engineering applications.

Estimation of stresses in a massive granite using laser ultra-sonic testing and stress memory effect

This paper addresses in-situ stress-estimation methods based on the Kaiser effect. The physical and mechanical properties of granite, diorite, and granodiorite samples selected at different depth intervals of the core obtained from a wellbore were examined. The ultimate uniaxial compressive strength, modulus of elasticity, and Poisson’s ratio of the rock samples were determined using presses and strain gauges. Also, local longitudinal and shear wave velocities were measured using a high-accuracy laser-ultrasonic system with a view to assessing the structure of the samples. Based on the resulting elastic wave velocity maps, samples with no obvious discontinuities were chosen. These undisturbed samples were subjected to uniaxial compression and their acoustic emission was simultaneously measured. In-situ stresses were estimated from the results of the interpretation of acoustic emission measurements. The experimental in-situ stresses were compared with the results of a numerical simulation. The ratio of the estimated in-situ stresses to the calculated ones is within the range from 0.81 to 1.11. This means that the laser ultrasonic and acoustic emission methods make it possible to effectively estimate in-situ stresses in a rock mass and assess the degree of rock mass damage.

Damage Effect of Thermal Shock on the Heated Granite at Different Cooling Rates

This study investigates the affecting pattern of cooling rates on the physical and mechanical properties of granite at high temperature. The different cooling rates are realized by cooling the heated granite specimens in the air at room temperature, −60 °C, and −100 °C. Slow cooling in the unplugged furnace is also performed on an additional set of specimens as a reference group. Physical and mechanical tests are performed on the granite specimens after thermal shock treatments. The results indicate a decreasing trend of the dry density, P-wave velocity, strength, and fracture toughness, and an increasing trend of the porosity, as the heating level or the cooling rate ascends. The microscopic observation on the fracture surface of the tested specimens manifests the deteriorating effect of thermal shock with a higher cooling rate, where the transition from trans-granular and intra-granular fracturing to intergranular fracturing serves to explain the variation pattern of the properties obtained in the lab tests.

Numerical investigation on the effect of intergranular contact bonding strength on the mechanical properties of granite using PFC3D‐GBM

AbstractIn rock materials, the intergranular structure is more affected by various external conditions than the transgranular structure, and then dominates the macroscopic mechanical properties of rocks. In this paper, an innovative three‐dimensional grain‐based model based on Particle Flow Code (PFC3D‐GBM) for reproducing granite crystalline structures was developed. Based on this model, the Brazilian splitting test was conducted to investigate the effects of intergranular contact (IC) bonding strength on the mechanical properties and micro‐cracking behavior of the granite. Additionally, in this paper, the force chains and the orientation distribution of the force chains are shown in the form of three‐dimensional rose diagrams. The results are compared to the numerical results obtained by an initial particle‐based model to demonstrate the superiority of the proposed PFC3D‐GBM. The results indicate that the stress–strain curve of the sample in the Brazilian splitting test can be classified into four distinct stages: initial compaction, linear elasticity, damage, and splitting failure. ICs fracture at a higher rate than transgranular contacts (TCs) under static loading, as evidenced by experimental results of laboratory tests; during the entire loading process, all force chains uniformly distribute in all directions of a sample. As the external load increases, the number of total force chains decreases and the number of cracks increases. The main orientation of the high‐strength force chains is consistent with the external loading direction and is vertical with respect to the main orientation of the cracks. Furthermore, the number of high‐strength force chains increases with the level of external load. The sample's failure mechanism in the Brazilian splitting test is always a tensile failure, and this characteristic is unaffected by the modeling method or the IC bonding strength. Both the tensile strength and peak strain increase as the IC bonding strength increases. In this process, the number of total cracks in PFC3D‐GBM decreases, the proportion of transgranular cracks (Tcs) increases, and the proportion of intergranular cracks (Ics) decreases. The micro‐cracking behavior described above based on the PFC3D‐GBM can be explained more rationally. As the bonding strength of the IC increases, the particles involved in sample deformation are subjected to a greater stress concentration prior to the sample experiencing macro‐fracture, leading to an increase in the number of high‐strength force chains, which is the fundamental reason for the increase of the sample's tensile strength.

Study on mechanical properties and acoustic emission response of deep granite under hydro-mechanical coupling

The study on the mechanical response of deep rock under hydromechanical couplings condition can guide the safe excavation and stability evaluation of deep tunnel engineering. The effects of monotonic loading and cyclic loading on the mechanical properties of granite under 5 MPa pore water pressure and 10 MPa confining pressure were studied by laboratory tests. Before the peak stress, the permeability under monotonic loading was significantly higher than that under cyclic loading, and the permeability under cyclic loading increased sharply after the peak stress. There were two active periods of the acoustic emission energy before peak stress under monotonic loading, but it was always in relative quiet period under cyclic loading before peak stress. Based on the energy theory, the energy evolution of granite was discussed. The dissipation energy can better reflect the effect of loading mode on the energy evolution.

Study on the mechanism of mechanical property strengthening of Beishan granite under mild temperature condition

Many researches found that mechanical properties of granite were strengthened under the mild temperature range (within 300 °C), which is positive for the long-term safety of the high-level radioactive waste (HLW) geological disposal engineering. To study the thermal strengthening mechanism of granite under elevated temperature by the decay heat of the HLW, a novel experiment was carried out which stress loaded firstly to cause stress damage, then thermal loaded to study the temperature effect on stress damaged granite. Results show: (1) the deformation memory effect and the Kaiser effect existed after stress loaded for non-thermal treated and 120 °C treated on granite, while the deformation memory effect (DME) was significantly faded after 250 °C treated. (2) The volume of pores/cracks in Beishan granite increased after stress loaded, then decreased significantly after 120 °C and 250 °C treated. (3) The deformation behavior, AE activity and pores/cracks closure all showed that the stress induced damage could be healed at elevated temperature, which is positive for the HLW disposal engineering. (4) A viscoelastic frictional sliding model was used to analyze the mechanism of DME fading and the mechanical property strengthening.

Permeability and Mechanical Response of Granite after Thermal and CO2 Bearing Fluid Hydro-Chemical Stimulation

The large scale extraction of geothermal energy can reduce CO2 emissions. For hot dry rocks, the key to successful utilization depends on the efficiency of reservoir reconstruction. The chemical and thermal stimulation methods are always used in geothermal reservoir reconstruction except in hydraulic fracturing with high fluid injection pressure, which is believed to reduce the seismic hazard by applying before the high-pressure hydraulic fracturing stimulation. However, at the laboratory scale, there are still very limited experimental studies illustrating the combined effects of chemical and thermal stimulation on the permeability and mechanical properties of granite, which is regarded as the main type of hot dry rock. In this paper, comparative stimulation experiments were carried out, including thermal/cold stimulation, CO2 bearing solution hydro-chemical stimulation, combined thermal and CO2 bearing fluid stimulation. By means of nuclear magnetic resonance analysis, permeability test and triaxial compression test, the changes of the micro-structure, permeability and mechanical properties of granite under various stimulation conditions were analyzed. The experimental results show that, compared with the single thermal stimulation and CO2 bearing fluid hydro-chemical stimulation, the superposition effect of thermal and CO2 bearing fluid hydro-chemical stimulation can increase the number of micro-fractures in granite more effectively, thus increasing the permeability, while the elastic modulus and compressive strength decrease. Moreover, the cooling mode on the granite also has a certain influence on the stimulation effect. After water-cooling on the heated granite (300 °C), combined with the CO2 bearing fluid stimulation (240 °C, 20 MPa), the permeability of granite is the highest, increasing by 17 times that of the initial state, and the porosity also increases by 144.4%, while the elastic modulus and compressive strength decrease by 14.3% and 18.4%, respectively. This implies that the deterioration of mechanical properties due to the micro-fractures increased by the thermal and chemical stimulation can enhance the fluid conductivity and heat extraction of granite. The methods in this paper can provide a reference for the combined application of thermal and chemical stimulation technology in artificial reservoir reconstruction of hot dry rocks.

Influence of cooling speed on the physical and mechanical properties of granite in geothermal‐related engineering

AbstractIn deep‐earth engineering, the high earth temperature can significantly affect the rock's mechanical properties, especially when the rock is cooled during the construction process. Accordingly, whether the cooling speed affects the mechanical and physical properties of rocks is worth to be investigated. The present study explored the influence of the cooling rate on the physical and chemical properties of granite heated at 25–800 °C. The mechanical and physical properties involved in this study included uniaxial compression strength, peak strain, modulus, P‐wave velocity, mass and volume, the change of which could reflect the sensitivity of granite to the cooling rate. Acoustic emission (AE) monitoring, microscopic observation, and X‐ray diffraction (XRD) are used to analyze the underlying damage mechanism. It is found that more AE signals and large‐scale cracks are accounted for based on the b‐value method when the specimens are cooled by water. Furthermore, the microscopic observation by polarized light microscopy indicates that the density, opening degree, and connectivity of the cracks under water cooling mode are higher than that under natural cooling mode. In addition, the XRD illustrates that there is no obvious change in mineral content and diffraction angle at different temperatures, which confirms that the change of mechanical properties is not related to the chemical properties. The present conclusion can provide a perspective to assess the damage caused by different cooling methods to hot rocks.