Rock Specimens Research Articles

A study on the effect of crack orientations, crack types and SHPB characteristics on the failure behaviour of pre-cracked sandstone rock specimens

The present study aims to understand the experimental and numerical behavior of intact and pre-cracked fine-grained sandstone specimens under indirect dynamic tensile loading conditions. The dynamic experimental analyses are carried out using the split Hopkinson pressure bar (SHPB) device to determine the tensile strength of sandstone rock. In addition to the dynamic tests, the physical, petrological, and mechanical tests under static loading of the sandstone rock are also studied. Thereafter, a three-dimensional (3D) finite element (FE) numerical model is developed, and a strain rate-dependent modified Drucker Prager constitutive model is used to validate the numerical model with the indirect dynamic tensile experimental test results. The validated parameters are then used to determine the behavior of pre-cracked sandstone specimens through numerical simulations. Two sets of numerical models with diametral cracks and cross-sectional cracks are introduced into the intact rock specimens. The orientation of the crack is changed from 0° to 90° and the numerical analyses are performed for 0°, 30°, 45°, 60°, 75° and 90° crack orientations with respect to the loading axis of the bars in the SHPB setup. Along with crack orientations, the loading rate is changed with varying gas gun pressures for the two sets of numerical models. The stress-strain responses are retrieved from the center and tip of the pre-crack introduced in the sandstone specimen. A comparative analysis is conducted for the responses obtained at the center and tip of the diametral and cross-sectional cracks and the results are stated herein.

The influence of desalinization of reservoir rocks on their mechanical and filtration properties using the example of the Chayandinskoye field

Using the Independent Triaxial Loading Test System of the Institute for Problems in Mechanics of the Russian Academy of Sciences (TILTS), rock specimens from the core material of the reservoir of the Chayandinskoye oil and gas condensate field were tested in order to experimentally study the effect of desalinization of reservoir rocks on their deformation, strength and filtration characteristics. It has been shown that desalinization sharply increases the permeability of rocks. At the same time, the deformation and strength properties of the studied rocks change towards softening (with the exception of the angle of internal friction), nevertheless remaining quite high. Experiments on physical modeling of the process of reducing pressure at the bottom of a horizontal well using TILTS showed that a slight decrease in the elastic and strength properties of the reservoir rocks of the Chayandinskoye oil and gas condensate field after their desalinization should not affect the stability of the well walls. The results obtained allow us to draw an important practical conclusion that when operating a field at the stage of salt washing out due to water filtration during operation, one should not expect a significant increase in the risks associated with reservoir destruction and increased sand production.

Size Effect on Shear Behaviors of 3D-Printed Soft Rock-like Materials Under Different Shear Velocities

The shear failure of rock masses is one of the primary causes of underground engineering instability. The shear mechanical behavior of rocks at different sizes is of great significance for studying the shear failure pattern of engineering rock masses. However, due to the presence of various joints and defects in natural rocks, the obtained rock specimens exhibit significant discreteness, making it difficult to customize specimen sizes for size effect studies. In recent years, 3D printing (3DP) technology has gained widespread application in rock mechanics tests due to its high printing precision and ability to form specimens in a single step with minimal discreteness. Among these, specimens prepared using sand-powder 3DP exhibit elastoplastic mechanical characteristics similar to those of natural rocks. Therefore, this study utilized sand-powder 3DP to prepare rock-like specimens of four different sizes and conducted compression shear tests under three different shear velocities. The shear strength, shear strain, and wear of the shear surfaces were analyzed as functions of specimen size and shear velocities. The results indicate that under the same shear velocity, the shear strength of the specimens is negatively correlated with specimen size. The peak shear strain is generally unaffected by shear velocities, but it increases initially and then decreases with increasing specimen size. As specimen size increases, the degree of specimen damage intensifies, and larger specimens are more prone to developing derived fractures. This study broadens the application of sand-powder 3DP technology in investigating the shear mechanical properties of soft rocks, offering novel insights into the study of size effects in rock mechanics. However, the current research does not encompass tests on 3D-printed rock specimens with varying printing directions, nor does it delve into the role of fractures in size effect analyses. Future investigations will aim to address these limitations, thereby advancing the applicability of 3D printing technology in rock mechanics research and enhancing its contributions to the field.

Investigation into the time-dependent mechanical behavior of pre-stressed anchor bolts and fractured rock specimens under synchronized tensile loads

Pre-stressed anchor bolts serve as an effective means to reinforce fractured rock masses. The long-term efficacy of their anchoring function significantly impacts the safety throughout the entire lifecycle of rock engineering projects. Over time, fractured rock masses undergo creep deformation, which interacts synergistically with the time-dependent changes in the pre-stress of anchor bolts. In this work, we conduct uniaxial tensile tests and tensile creep tests on fractured rock specimens anchored by pre-stressed bolts, analyzing the coordinated deformation between the pre-stressed anchor bolts and the fractured specimens. Firstly, conventional uniaxial tensile tests were conducted on the pre-stressed anchorage specimen. The study found that the tensile strength of the anchored specimens was significantly higher than that of the unanchored specimens. Additionally, the ability of the specimens to withstand tensile stresses and deformation improved as pre-stress increased. Secondly, uniaxial tensile creep tests were conducted on the prestressed anchored specimens. The results indicate that, as the stress level increases, the creep strain continues to increase. The application of prestress can effectively limit the tensile deformation of the specimen and delay its damage time. The greater the pre-stress, the smaller the instantaneous strain and creep strain rate during the graded loading test. Finally, based on the synergistic deformation of pre-stressed anchor bolts and the creeping rock mass, we establish a constitutive model reflecting the creep properties of fractured rock mass and derive a theoretical viscoelastic creep formula for anchored rock mass under uniaxial tension. Comparing the creep model with the test results shows that this model is highly applicable and accurate in verifying the tensile creep deformation of prestressed anchorage specimens.

Leeb hardness test as a tool for joint wall compressive strength (JCS) evaluation

The Barton-Bandis model for the nonlinear shear strength of rock joints is the most commonly used strength criterion in rock engineering practice. There have been advancements in determination of Joint Roughness Coefficient (JRC), such as the use of laser scanning; however, the equally important Joint Wall Compressive Strength (JCS) parameter has not been significantly advanced. The JRC and JCS are effectively linked, to some extent. A sensitive rebound hardness index test, the Leeb Hardness (LH) test, was investigated to provide a quantifiable and repeatable method of JCS determination that offers increased accuracy relative to current methods. The LH test value (LD) correlation to Unconfined Compressive Strength (σc) is proposed for JCS determination. In addition, this study investigates the Influence Zone of the LH test on surfaces with graded hardness profiles (e.g., weathered surfaces). This was done using a series of artificial composite plaster-rock specimens of known hardness to provide insight into the influence effects on the surface LD reading due to underlying material of contrasting hardness. In addition, a collection of natural rock specimens with variable joint wall hardness were collected and LD profiles were obtained by sequential surface grinding and testing. These natural rock specimens included those with wall surface materials softer and harder relative to the underlying intact rock. A Hardness Contrast Type was proposed for classification of hardness contrast conditions. The study findings showed the LH test is a suitable tool for predicting JCS and a proposed methodology was presented.

Experimental Study on Deformation and Damage Evolution of Cracked Red Sandstone Under Freeze–Thaw Cycles

Cracked rock masses in cold regions are subjected to freeze–thaw cycles over extended periods, resulting in freeze–thaw deformation. The combined effects of freeze–thaw cycling and the depth of cracks significantly influence the stability and durability of underground rock engineering in these regions. In some cold regions with minimal annual rainfall, rock masses are unable to absorb external water during freeze–thaw cycles. As freeze–thaw deformation progresses, the rock transitions naturally from a saturated state to an unsaturated state. To investigate the deformation damage mechanisms and evolution patterns of saturated red sandstone with initial non-penetrating cracks of varying depths (20 mm, 30 mm, 40 mm) under freeze–thaw cycling conditions without external water replenishment and with naturally varying saturation levels, relevant freeze–thaw cycle experiments and strain monitoring were conducted. The results indicate that cracked red sandstone experiences residual strain in each freeze–thaw cycle, which gradually accumulates, leading to irreversible freeze–thaw damage deformation. The cumulative residual strain of the rock specimen after 45 freeze–thaw cycles was 40.69 times greater than the residual strain from the first cycle. Additionally, the freeze–thaw strain characteristic values exhibited a clear correlation with crack depth. These findings provide experimental methods and data references for analyzing the deformation and failure mechanisms of cracked rock induced by freeze–thaw damage in cold regions.

Experimental Investigations on Repair and Permeability Reduction for Single Sandstone Fracture Using a Mixed CaCO3 and Fe(OH)3 Precipitate

In China, groundwater loss caused by underground coal mining is becoming increasingly serious. The key to groundwater restoration is to repair mining-induced water-conducting fractures (WCFs) in the overlying strata. In this study, the adsorption–consolidation sealing characteristics of chemical precipitates were used to conduct permeability reduction (PR) experiments, including adding mixed CaCO3 and Fe(OH)3 to a sandstone specimen with a single fracture at room temperature. An aqueous solution of Na2CO3 was used as the simulated groundwater, and a solution of mixed CaCl2 and FeCl2 was used as the repair reagent to simulate the water seepage conditions of a fractured rock mass. The two aqueous solutions were simultaneously injected into a single-fractured rock specimen at a constant flow rate. The experimental results show that the Fe(OH)3 colloid encapsulated CaCO3 crystals in a mixed precipitate, reducing the overall structural stability of the mixed precipitate and restricting repair and PR efficiency. However, the Fe(OH)3 precipitate had better PR efficiency in the initial stage of the experiment. Therefore, a better scheme was put forward to repair the WCF, utilizing a mixed Fe(OH)3 and CaCO3 precipitate with a molar ratio close to 1:4 in the early stage and a single CaCO3 precipitate in the later stage.

Comparative analysis of the performance of Thin Spray-on Liner with shotcrete and mesh support

In order to study the effect of different surface protection components, such as Thin Spray-on Liner (TSL), in the support system of prestressed bolts on the critical rock mass, based on the similarity theory, physical modeling tests were designed and carried out for the support of the critical rock mass by the combination of NPR bolts and PR bolts with three types of surface protection components, such as TSL, sprayed concrete, and metal mesh, respectively. The test results show that the three types of surface protection components can significantly increase the threshold value of crack development of the critical rock specimen and effectively improve the peak bearing capacity of the critical rock body, and at the same time, the NPR bolts with higher strength and elongation have a more significant effect on the improvement of the peak bearing capacity of the critical rock specimen. In addition, TSL and spray-mixed support and specimen surface can realize close fit, in the loading of the early support response is more timely, in the late loading, compared with the spray-mixed material in the rupture of debris collapse, TSL in the occurrence of tearing can still be tightly adhered to the specimen proximity surface of the rock specimen, to prevent specimen debris fall. For the phenomenon of TSL coating rupture in the experiments, the energy balance equation was established to analyze the connection between the actual energy absorption effect and the theoretical value of the combination of TSL and bolts under the pre-stressed bolts support system, and it was found that the combination of pre-stressed bolts and TSL greatly improved the actual energy absorption effect of the support system as a whole, and the analytical results of the various experimental subgroups showed better results than the theoretical values. The analysis results of the subgroups show a good fit.

Analysis of the changes in filtration and capacity properties of the oil and gas condensate field reservoirs using X-ray computed tomography methods

Objective. To study the nature of changes in structural, capacity and filtration properties of the Chayanda oil and gas condensate field reservoir resulting from mechanical and hydrodynamic testing and to improve the quality of laboratory assessment of the reservoir properties of rocks by applying the digital approach. Materials and methods. A high-resolution X-ray micro-CT scanner ProCon X-Ray CT-MINI was used for computed tomography. Digital analysis of images was carried out in GeoDict software. Results. The results of digital analysis of changes in the pore space of hydrocarbon reservoir by computer tomography methods after the tests with fluid filtration under baric conditions are presented, including comparison of macroscopic changes in the pore space and determination of the nature of changes in reservoir porosity and pore geometry at the macro level. Porosity values were determined using digital methods and compared with laboratory data. Numerical modeling of filtration processes on the created 3D models of the rock was performed. The fact of nonuniform distribution of filtration flows was established: filtration in the rock occurs mainly through isolated alternating channels. It was determined that the change in the rock pore space occurred mainly due to deformation and expansion of the walls of the main filtration channels. Conclusions. Nonuniformity of changes in filtration-capacitance properties of rock specimens caused by mechanical and hydrodynamic tests can lead to incorrect estimation of porosity and permeability when applying traditional laboratory methods. The results of nondestructive digital studies can be advised as a supplement to laboratory studies of core material properties. Joint application of digital and traditional laboratory methods allows obtaining the most complete range of data on reservoir properties to solve problems arising during development.

Study on mechanical properties and acoustic emission characteristics of composite rock mass with different thicknesses of weak interlayer

To study the influence of the thickness of a weak interlayer on the deformation and failure characteristics of composite rock mass. Based on the measured data of sand-mudstone interbedded floor rock mass in the Yima mining area, Henan Province, China. Using quartz sand, gypsum, and cement as similar materials make composite rock-like specimens with weak interlayers. The mechanical properties, deformation evolution process, failure characteristics, and acoustic emission laws of rock samples with different interlayer thicknesses under uniaxial compression were studied using the digital image correlation method and acoustic emission monitoring technology. The results show that: (1) With an increase in the thickness of the weak interlayer, there is a corresponding decrease in the compressive strength of the specimen. When the thickness of the weak interlayer exceeds 5 cm, the compressive strength of the composite rock specimen is even less than that of the single weak rock-like. (2) Under uniaxial compression conditions, the strain concentration zone first appears in the weak interlayer part of the composite rock-like specimen. As the pressure continues to increase, the specimen is the first to fail at the position of the maximum strain concentration zone. (3) The thickness of the weak interlayer is an important factor affecting the failure mode of composite rock-like specimens. With the increase of the thickness of the weak interlayer, the composite rock-like specimens change from overall failure to local failure. (4) With the increase of the thickness of the weak interlayer in the middle of the composite rock specimen, the maximum value of the energy released by the single acoustic emission event and the maximum value of the cumulative acoustic emission energy decrease during the compression failure process. The research results can provide a reference for the manufacture of composite rock mass with a weak interlayer and the deformation and failure analysis of composite rock mass.

Experimental and Numerical Indentation Tests to Study the Crack Growth Properties Caused by Various Indenters Under High Temperature

ABSTRACTThis paper investigates the influence of indenter shape and rock texture on the crack growth properties and rock hardness. For this purpose, two different rock specimens such as basalt and marble with various textures were prepared and tested by Vickers indentation hardness device with rhombus indenter shape under two different temperatures of 35°C and 100°C. Concurrent with the experimental test, Vickers indentation simulations have been done on three calibrated rock models with nine different indenter shapes. The tensile strength of marble was 8 MPa, while basalt had a tensile strength of 10.8 MPa. Regarding compressive strength, marble exhibited 71 MPa, whereas basalt had a compressive strength of 153 MPa. Marble and basalt had elastic moduli of 45 and 95 GPa, respectively. The physical loading was applied vertically at a rate of 0.004 mm/min. The rock's texture and temperature significantly impact Vickers indentation hardness. Penetration by the Vickers indenter creates an elastic‐plastic stress field, leading to radial cracks due to exceeding the critical stress level. Ring cracks are caused by bulging of the test material and nested cracks directly under the indentation due to high shear and bending stresses in the region. The indentation shape affected the extent of the damage zone below it, leading to increased crack growth with smaller indentation diameters. The radial fracture number increased when the cross‐section changed from circular to quadrilateral shape. The crack growth and damage zone area increased with higher rock temperature due to increased rock brittleness.

Direct Shear Testing Apparatus for Saturated Rock Joints

Abstract A novel shear test apparatus has been designed and built to test saturated jointed rock specimens under normal and shear loading, capable of housing seismic transducers to monitor simultaneously the mechanical and geophysical response of the rock joints during shear. The system comprises a sealed pressure chamber and a biaxial compression frame. The internal dimensions of the chamber are 177.8 mm × 228.6 mm × 381.0 mm to accommodate a rock specimen with dimensions 152.4 mm × 127.0 mm × 50.8 mm. The chamber is made of aluminum to reduce its weight and is designed to sustain a maximum chamber pressure of 10 MPa, which is considered sufficient to be able to saturate a wide number of rocks. Structural calculations of the chamber are performed with the finite element method (FEM) software, ABAQUS, with the criterion of a maximum deflection of 1 mm at maximum chamber pressure, which is small enough to prevent the loss of seal between the loading shafts and the chamber. The rocks used in the study are Indiana limestone and Sierra White granite. B-value tests conducted on cylindrical specimens of the rocks placed inside the chamber show that the back pressures required to achieve saturation are 3.5 MPa for Indiana limestone and 5.0 MPa for Sierra White granite. The chamber performance has been evaluated by comparing the changes of volume of the chamber at different pressures, measured in the laboratory, with those predicted with ABAQUS. The successful completion of a number of repeatable direct shear tests, on tensile-induced rock joints in dry and saturated conditions specimens, has further established the correctness of the chamber design and its operation.

Cracking and deformation behaviors of overhanging rock: Laboratory tests and optical monitoring

The destabilization of overhanging rock is a dangerous geological problem. In this study, a generalized model of typical overhanging cliffs from the Three Gorges Reservoir area in China with different fracture angles, fracture lengths, and free surface depths is constructed to investigate the cracking and deformation behavior of overhanging rocks. Laboratory tests and deformation field monitoring using the digital image correlation (DIC) method are performed on these specimens to reproduce the destabilization and failure process of overhanging rock under external loading. The influence of peak load is found to be the most sensitive to the fracture length, followed by the free surface depth, and to be the least sensitive to the fracture angle. The DIC-based strain fields reveal that the fracture angle and free surface depth significantly alter the crack propagation paths, whereas the influence of the fracture length is weaker. These parameters also affect the crack initiation time. The relative displacement evolution characteristics indicate that fracture angle, fracture length, and free surface depth affect the shape and size of the rotating block, the rotation center, and the rotation pivot point and degree, respectively. The grayscale characteristic evolution trends are similar for all examined overhanging rock specimens. The evolution of the grayscale indices based on DIC can be divided into high-frequency oscillation, smooth decline (or smooth downward concavity), and stable development stages. Furthermore, the multistage properties of the indices can be used to identify the fracture state of overhanging rocks, providing a theoretical basis for graded early warning of rockfall disasters.

Fracturing Process Visualization of Cracked Chevron-Notched Brazilian Discal and Notch Semicircular Bend Rock Specimens and Comparative Analysis by Combined AE and DIC

Abstract A series of homogeneous granite specimens were prepared to investigate the Mode I fracture toughness (KIC) using the cracked chevron-notched Brazilian disk (CCNBD) method and semicircular three-point bending (NSCB) method recommended by the International Society for Rock Mechanics (ISRM). A combination of acoustic emission (AE) and digital image correlation (DIC) was utilized to monitor the crack propagation and analyze the fracture modes at various test stages. The results indicated that the average value of Mode I fracture toughness (KIC-) of the CCNBD specimen was approximately 10% higher than that of the NSCB specimen. The coefficient of variation in the NSCB test was small, which could provide more stable result of Mode I fracture roughness. Compared to the CCNBD test, the failure mode of NSCB specimens was mainly tensile damage with instantaneous damage during the experimental process. Furthermore, the failure process of the NSCB test was mainly controlled by tensile fractures, which exhibited instantaneous failure. The CCNBD test was first controlled by tensile fractures and then by shear fractures when the peak was reached, exhibiting progressive failure. The failure mode and the process may be the main factors controlling the difference between the results of the NSCB and CCNBD tests. This work helps select appropriate methods to measure the Mode I rock fracture toughness.

Effect of microwave heating on rock damage and energy evolution

Rock fragmentation efficiency can be increased by microwave heating. The mechanical properties and energy evolution characteristics of coarse sandstone specimens under different microwave heating conditions are compared in this paper. The effects of microwave heating time and power on coarse sandstone specimens of peak stress, elastic modulus, brittleness index, damage variable, and impact energy index are analyzed. The results indicate that the microwave heating power and microwave heating time are inversely proportional to peak stress and elastic modulus and directly proportional to peak strain. With the increase of microwave heating power and microwave heating time, the brittleness index and damage variable of rock specimens increase, the impact energy index decreases. The microwave heating power and microwave heating time increase the rock brittleness index. The energy absorption rate of rock specimens decreases with the increase of microwave heating time. The impact energy index is inversely proportional to microwave heating power and microwave heating time. High-power and long-time microwave heating can reduce the possibility of rockbursts and the intensity of potential dynamic disasters. The research conclusion can provide the theoretical and technical basis for breaking rock by microwave heating.

Experimental Investigation on Rock Failure Characteristics of Large-Span Goafs Using Digital Image Correlation Analysis and Acoustic Emission Monitoring

Rockmass in deep mining is highly susceptible to large-scale collapses under high stress and blast-induced disturbances, leading to casualties and economic losses. To investigate the evolution characteristics of goaf instability and the types of seismic sources that induce instability, an experiment on goaf instability was designed under uniaxial compression conditions based on actual mining operations. The entire experimental process was monitored using digital image correlation analysis and acoustic emission monitoring. By calculating the digital speckle field on the surface of the rock specimen during the experiment, the evolution characteristics of the deformation and strain fields from the beginning of loading to complete failure were analyzed. The study explored the dynamic behavior of cracks from initiation to propagation and eventually inducing large-scale collapse. The results show that the instability process of the goaf begins with the formation of tensile cracks. As stress increases, shear cracks occur in the specimen, leading to macroscopic failure. Furthermore, based on the differences in overall microfracture types measured by RA-AF characteristic parameters during specimen failure, large amplitude acoustic emission events corresponding to the formation of dominant macroscopic cracks were selected, and the focal mechanisms of these events were inverted. The results indicate that shear failure sources are significantly more prevalent than tensile failure sources in acoustic emission events leading to goaf instability. These findings can provide useful guidance for the support design and the prevention and control of rockmass instability disasters.

A novel experimental method for studying rock collision

This paper introduces a new experimental method for studying rock collision by making full use of the beauty of stress wave theory. In this method, a newly developed energy transmission component was placed between the gas gun and the transmitted bar of a split Hopkinson pressure bar (SHPB). The forementioned component consists of an incident bar which moves frictionlessly within a specified distance, a circular steel plate welded to the incident bar, and a support base which is bolted to the SHPB bed. A rock specimen is attached to the farther end of the incident bar. When the striker bar, propelled by the gas gun impacts the incident bar, a compressive stress wave is transmitted from the incident bar to the rock specimen. When the compressive wave arrives at the free end of the rock specimen, it is reflected into a tensile wave. Then when the pure stress becomes tensile and it is over the tensile strength of the glue at the interface between the rock specimen and the incident bar, the rock specimen is ejected, and then the ejected specimen will collide with the transmitted bar. During specimen flight, the velocity of the rock specimen can be measured by a laser instrument, while the remained energy transferred to the transmitted bar is measured by strain gauges attached to it. The process of rock specimen flight before collision and fragment flight after collision can be photographed using a high-speed camera. This experimental method can be used to not only study a collision between a moving rock and another object, but also imitate a drop weight test. By using this new method, seven rock collision tests were successfully conducted.

Retraction Note: Effects of size and strain rate on the mechanical behaviors of rock specimens under uniaxial compression

Retraction Note: Effects of size and strain rate on the mechanical behaviors of rock specimens under uniaxial compression

Research on coal-rock boundary identification based on the morphological sobel algorithm

Due to the harsh underground environment during coal mining, the quality of images collected by cameras is not sufficient, and the acquired images are greatly affected by noise, affecting visual observation; to a certain extent, subsequent intelligent mining is limited. A morphological Sobel coal-rock boundary recognition algorithm is proposed according to the different gray levels of coal-rock images to solve the problem of coal image quality. First, the details of the coal and rock images are smoothly preprocessed to improve the contrast between the feature boundaries and surrounding pixels, and the gray-level adaptive threshold is applied after processing. Morphological corrosion theory is used to process the morphological structure in an image, and the corresponding boundary in the image is extracted for recognition. Compared with the boundary points identified by each algorithm, the area error of coal and rock identification is calculated by using the boundary point fitting curve. The morphological Sobel algorithm is used to calculate the identification area error of coal and rock at different angles according to the camera range. The experimental results show that the boundaries identified by the morphological Sobel algorithm have the best degree of overlap with the boundaries of the original image. The identification error area is only about 10% of the Sobel operator and Canny operator algorithm. Monitoring coal and rock specimens can enable the effective identification of coal and rock boundaries from various angles.

Changes in the nanomechanical properties of the constituent minerals in the ductile fauske marble and the brittle kuru granite during progressive failure

The nanoscale elastic moduli and hardness of the constituent minerals of the Class II Kuru granite and the Class I Fauske marble were experimentally investigated. The aims were to correlate the microcrack patterns with the nanomechanical properties of the minerals, and to help understand the important roles of the nanomechanical properties of the minerals in brittle and ductile behaviors. Cylindrical rock specimens were uniaxially loaded to various stress levels in both the pre- and post-peak stages. The specimens were then unloaded to zero, and two thin sections –– one parallel with and the other perpendicular to the loading direction –– were prepared from each specimen. Nano-indentation tests were conducted on the thin sections to measure the elastic moduli and hardness of the major constituent minerals in the rocks. The test results showed that both the elastic moduli and hardness of the minerals abruptly decreased when the applied stress was above 80 % of the uniaxial compressive strength of the rock in the pre-peak stage and also in the entire post-peak stage. At the same time, the values of the two properties became more scattered with increasing damage to the minerals. The number of intragranular cracks was significantly less in the harder quartz and microcline than in the softer calcite. The abundant intragranular cracks in the calcite dissipated most of the strain energy in the Class I marble, such that the rock was not burstable after failure. A small number of intragranular cracks were created in the quartz and microcline in the Class II granite, such that most of the strain energy in the minerals was released to eject rock after failure. Intragranular cracking is thus a key factor in determining whether a rock is burst-prone or not.