Mechanical Properties Of Sandstone Research Articles

Numerical investigation on the influence of CO2-induced mineral dissolution on hydrogeological and mechanical properties of sandstone using coupled lattice Boltzmann and finite element model

Numerical investigation on the influence of CO2-induced mineral dissolution on hydrogeological and mechanical properties of sandstone using coupled lattice Boltzmann and finite element model

Dynamic failure behaviour of sandstone with filling joints using the Brazilian disc method

Rock masses contain joints often filled with low-strength materials such as mud and gum. The instability mechanism of a filled jointed rock mass under dynamic loads is complex, posing challenges for disaster control. Splitting tests were conducted using a split Hopkinson pressure bar device and a high-speed camera to investigate the effects of weak-filling joints at various angles on the failure mechanism and mechanical properties of sandstone. The typical failure processes, splitting mechanical properties and fracture morphologies were analysed. The results indicated that as the joint angle increased from 0 to 90°, the crack coalescence pattern of the jointed sample under static and dynamic splitting loads evolved from complete separation along the bonding surfaces to shear–slippage failure along the direction of the joint angle and tensile–shear failure with a dominant zigzag track, ultimately leading to typical tensile failure. Under dynamic loads, filled joints reduced the brittleness of the samples, contrary to the behaviour observed under static loads. The peak load and displacement were proportional to the joint angle and impact gas pressure, respectively. The fracture surface morphology precisely reflected the macroscopic fracture mechanism at the microscopic scale.

Study on Microscopic Characteristics and Rock Mechanical Properties of Tight Sandstone after Acidification–Supercritical CO2 Composite Action: Case Study from Xujiahe Formation, China

Acidified CO2 fracturing is a viable method for increasing production in deep, tight sandstone reservoirs. However, the potential mechanism of changes in pore structure and mechanical properties of sandstone under acidified CO2 supercritical composite is not clear. Understanding this mechanism is important for the study of crack initiation and extension in tight sandstone reservoirs. This study utilizes sandstone samples from the Xujiahe Formation reservoir in Rongchang District as experimental specimens. The primary focus is to analyze the changes in pore structure and mechanical properties of these samples after acidification–supercritical CO2 composite action. Nuclear magnetic resonance (NMR) and uniaxial compression tests are employed as the main investigative techniques. The results show that there was a physicochemical synergy between the acidification–supercritical CO2 composite effect; the crack initial stress, damage stress, and peak stress of the sandstone after 16 MPa supercritical CO2 acidification treatment were reduced by 20%, 49.5%, and 49.8%, respectively; the crack volumetric strain accelerated and the sandstone evolved from brittle to ductile damage; and the larger pore space and microcracks of the sandstone increased significantly after the treatment, which can be attributed to the gradual dissolution of intergranular cement leading to the formation of new pores connected to the existing pore network. The change mechanism of sandstone after acidification–supercritical CO2 compound treatment is also proposed.

Physical and Mechanical Properties and Damage Mechanism of Sandstone at High Temperatures

The physical and mechanical properties of rocks change significantly after being subjected to high temperatures, which poses safety hazards to underground projects such as coal underground gasification. In order to investigate the effect of temperature on the macroscopic and microscopic properties of rocks, this paper has taken sandstone as the research object and conducted uniaxial compression tests on sandstone specimens at different temperatures (20–1000 °C) and different heating rates (5–30 °C/min). At the same time, the acoustic emission (AE) test system was used to observe the acoustic emission characteristics of the rock damage process, and the microstructural changes after high temperature were analyzed with the help of a scanning electron microscope (SEM). The test results show that the effect of temperature on sandstone is mainly divided into three stages: Stage I (20–500 °C) is the strengthening zone, the evaporation of water and the contraction of primary fissures, and sandstone densification is enhanced. In particular, the compressive strength and elastic modulus increase, the macroscopic damage mode is dominated by shear damage, and the fracture micromorphology is mainly brittle fracture. Stage II (500–600 °C) is the transition zone, 500 °C is the threshold temperature for the compressive strength and modulus of elasticity, and the damage mode changes from shear to cleavage damage, and the sandstone undergoes brittle–ductile transition in this temperature interval. Stage III is the physicochemical deterioration stage. The changes in the physical and chemical properties make the sandstone compressive strength and modulus of elasticity continue to decline, the macroscopic damage mode is mainly dominated by cleavage damage, and the fracture microscopic morphology is of a more toughness fracture. The effect of different heating rates on the mechanical properties of sandstone was further studied, and it was found that the mechanical properties of the rock further deteriorated under higher heating rates.

Experimental Study on the Effect of High Temperature on the Physical and Mechanical Properties of Sandstone with Different Bedding Angles

As a typical sedimentary rock, the number of beddings in the horizontal direction of sandstone is far greater than that in the vertical direction, leading to its physical and mechanical properties showing obvious anisotropy with changes in bedding angle. After high temperature exposure, bedding damage further transforms the change rule of the physical and mechanical properties of sandstone with the bedding angle. This study tested the appearance, wave velocity, uniaxial compression, and conventional triaxial compression properties of sandstone with five bedding angles before and after high temperature exposure. The results show that (1) the longitudinal wave velocity, shear wave velocity, elastic modulus, and cohesion decreased, while the internal friction angle increased slightly. At the same temperature, when the dip angle of sandstone was 30° or 60°, the mechanical properties were optimal, and when the dip angle was 45°, the mechanical properties were the worst. (2) High temperature increases the development degree of micropores and microfractures in the sandstone bedding plane and matrix, thus increasing the anisotropy degree of the physical and mechanical properties of sandstone with different bedding angles. (3) With increasing temperature, the rock samples gradually transitioned from brittle failure to ductile failure. Sandstone with a bedding angle of 0° presented splitting failure that vertically penetrated the bedding plane at different temperatures. Sandstone with dip angles of 30° and 40° presented shear failure that penetrated the matrix and bedding plane. A failure plane along the bedding plane appeared at the end. Sandstone with dip angles of 60° and 90° was more prone to failure along the bedding plane, showing shear failure along the bedding plane and tensile failure along the bedding plane, respectively.

Mechanical behavior and fracture characteristics of high-temperature sandstone under true triaxial loading conditions

To understand the stability of deep underground engineering rocks at high temperatures, it is necessary to conduct comprehensive tests on the mechanical properties of the rocks. In this study, a series of true triaxial tests (TTT) were conducted on sandstones using a self-developed true triaxial testing system combined with XRD, FE-SEM and CT analyses. The study systematically examined the microstructural characteristics, physical phase behavior, deformation properties and internal fracture development of the sandstone before and after heat treatment. The results of the study show that sandstone has temperature-dependent true triaxial mechanical properties after heat treatment. The stress-strain characteristic curves of the post-peak portion from room temperature to 800 °C show a significant stress-reducing segment, indicating the presence of brittle behavior. In addition, when the temperature exceeds 1000 °C, the sandstone exhibits brittle-ductile change characteristics, with a peak stress threshold observed at 800 °C. Notably, the peak stresses corresponding to 800 °C increased by 84.5 %, 63.1 %, 47 %, and 49.8 %, respectively, compared with the room temperature intermediate principal stresses(IPS) ranging from 20 MPa to 50 MPa, respectively. Importantly, the linear Mogi-Coulomb criterion remains valid for the peak strength of the high-temperature sandstone, while the internal fracture damage pattern of the specimens shows an inverted "Y" or inverted "W" configuration. The internal fracture network of rock samples above 800 °C is more complex. Intergranular crack is the main form of microcracking. This experimental study on the mechanical properties of sandstone under the combined effects of high temperature and real triaxial stresses provides valuable guidance for the selection of sandstone parameters and safety evaluation of coal underground gasification roofs.

Microstructural and thermal properties of coal measure sandstone subjected to high temperatures

To study the microscopic structure, thermal and mechanical properties of sandstones under the influence of temperature, coal measure sandstones from Southwest China are adopted as the research object to carry out high-temperature tests at 25 °C–1000 °C. The microscopic images of sandstone after thermal treatment are obtained by means of polarizing microscopy and scanning electron microscopy (SEM). Based on thermogravimetric (TG) analysis and differential scanning calorimetric (DSC) analysis, the model function of coal measure sandstone is explored through thermal analysis kinetics (TAK) theory, and the kinetic parameters of thermal decomposition and the thermal decomposition reaction rate of rock are studied. Through the uniaxial compression experiments, the stress‒strain curves and strength characteristics of sandstone under the influence of temperature are obtained. The results show that the temperature has a significant effect on the microstructure, mineral composition and mechanical properties of sandstone. In particular, when the temperature exceeds 400 °C, the thermal fracture phenomenon of rock is obvious, the activity of activated molecules is significantly enhanced, and the kinetic phenomenon of the thermal decomposition reaction of rock appears rapidly. The mechanical properties of rock are weakened under the influence of rock thermal fracture and mineral thermal decomposition. These research results can provide a reference for the analysis of surrounding rock stability and the control of disasters caused by thermal damage in areas such as underground coal gasification (UCG) channels and rock masses subjected to mine fires.

Research and analysis of the impact of the pore structure on the mechanical properties and fracture mechanism of sandstone

Rock pore structure, including porosity, pore size, and particle size, plays a crucial role in determining rock mechanical properties. This study investigates the impact of pore structure on rock mechanical properties through laboratory experiments and numerical simulation methods on sandstones with varying porosity and pore size. The pore structure characteristics of sandstone were determined using XRD, SEM, and NMR microscopic techniques. Additionally, the influence of rock porosity on rock mechanical properties was analyzed by combining Uniaxial compression test with DIC technology, revealing the fracture mechanism caused by porosity in rocks. Numerical models were constructed to simulate sandstones with different porosities and pore diameters, followed by uniaxial compression simulation tests to explore the influence of varying pore diameters on rock mechanical properties and the fracture mechanism. The study reveals the presence of four distinct pore types in the sandstone: micropores in the matrix (0–0.002 µm), intergranular pores (0.002–0.2 µm), dissolution pores (0.2–4 µm), and fracture pores (4–30 µm). Among these, intergranular pores and dissolution pores are the predominant types, accounting for approximately 92–96% of the total pore volume in the sandstone. It is observed that an increase in porosity leads to a decrease in the mechanical strength of sandstone and an increase in Poisson's ratio while keeping the pore size constant. Similarly, when the porosity remains constant, an increase in pore size results in a decrease in the mechanical strength and an increase in Poisson's ratio. Additionally, the study also finds that as the porosity and pore diameter of sandstone increase, the area of internal equivalent stress expands, leading to a shorter crack initiation time and accelerated crack penetration speed, ultimately resulting in a decline in the mechanical properties of sandstone. Numerical simulation experiments further demonstrate that large pores exhibit higher stress concentration compared to small pores, thereby exerting a more significant influence on the mechanical properties of sandstone.

Creep mechanical properties and creep damage model of sandstone considering temperature effect based on acoustic emission

AbstractThis work studies the creep mechanical properties and creep damage model of high‐temperature heat treated sandstone. Acoustic emission (AE) technology is used to monitor the crack evolution of sandstone in uniaxial compression and creep experiments in real time. The influence of temperature on the mechanical properties of sandstone is analyzed through AE count, cumulative AE count, and AE absolute energy. The relationship between cumulative AE count and axial strain is discussed, and the cumulative AE count increases exponentially with increasing axial strain. Moreover, an appropriate damage evolution equation is established based on the cumulative AE count, and a nonlinear viscoelastic‐plastic model capable of describing the decay creep, steady‐stage creep, and accelerated creep stages of high‐temperature heat treated sandstone is constructed. Through the model validation and parameter inversion, the new creep damage model can be employed to study the creep instability of geotechnical engineering under high temperature environment.

Experimental study on deterioration of bedrock strength and P-wave velocity by pressurized seawater

Bedrock has to be excavated before the construction of rock-socketed pile foundations for offshore wind power turbines, leading to the exposure of fresh and dry rocks to seawater. The pile-rock interface is partially separated under the long-term action of various cyclic loads during the operation stage of offshore wind turbines, and the infusion of seawater will further weaken the bedrock. To comprehensively investigate the deterioration of bedrocks by pressurized seawater, tests on point load strength and slake durability were carried out to study the long-term deterioration of mechanical properties of granite, sandstone, and tuff collected from an offshore wind power farm. The elastic P-wave velocity was measured to analyze the variation trend of P-wave velocity, the mechanism of which was revealed by means of Gassmann’s equation. The results of mechanical experiments indicate that granite is almost impervious to pressurized seawater, while the mechanical properties of sandstone and tuff are deteriorated by water, especially by the pressurized seawater. After 60 days of immersion in seawater at 0.5 MPa pressure, decreasing amplitude of point load strength and slake durability index for the sandstone specimens in seawater reaches 53.2% and 18.5%, respectively, and that for the tuff specimens is 14.6% and 1.52%, respectively. The elastic P-wave velocity of granite shows an upward trend with increasing immersion time in different environments, but there exists a different tendency between the P-wave velocity of sandstone and tuff specimens in water or seawater with normal pressure and that in seawater with 0.5 MPa pressure. The variation of P-wave velocity of different types of rocks is studied based on Gassmann’s equation that takes into account the change of saturation degree, porosity, and compressibility of the matrix material.

Effects of ice content on compression characteristics of frozen sandstone by in-situ NMR technology

In cold regions, the freezing of pore water in rock affects the mechanical behavior of the rock. This paper studied the ice content of frozen sandstone at different temperatures and its effects on the mechanical properties of sandstone. First, the progressive freezing treatment (from 25.0 to − 30.0 °C) and in-situ nuclear magnetic resonance test were conducted to study the evolution of the ice content of sandstone with temperature. This evolution was quantitatively described by the frozen ratio defined as the percentage of the mass of ice and the total mass of water. Then, the mechanical properties of frozen sandstone at different temperatures (25.0 °C, 0.0 °C, − 5.0 °C, − 10.0 °C, − 20.0 °C and − 30.0 °C, respectively) were tested, such as P-wave velocity, uniaxial compressive strength (UCS), peak strain and elastic modulus. Finally, the effects of the frozen ratio on these properties were discussed. The results show that the pore water in sandstone shows three stages as the temperature decreases: stable liquid (from 25.0 to 0.0 °C), sharp phase transition (from 0.0 to − 2.5 °C) and slow phase transition (from − 2.5 to − 30.0 °C). Especially, the capillary and bulk water in sandstone is almost completely frozen in the sharp phase transition stage. As the temperature decreases, the frozen ratio first remains constant, then increases rapidly and finally increases slowly. Moreover, as the frozen ratio increases, the P-wave velocity, UCS and peak strain increase while the elastic modulus decreases. Interestingly, the compressive failure mode of sandstone changes from brittle to ductile as the frozen ratio increases.

Experimental Study of the Mechanical and Acoustic Emission Characteristics of Sandstone by Using High-Temperature Water-Cooling Cycles

In order to study the physical and mechanical properties of sandstone under high-temperature water-cooling cycling conditions, an RMT-150B electrohydraulic servo rock testing system and a DS-5 acoustic emission detection and analysis system were used to conduct uniaxial compression acoustic emission tests on sandstone after high-temperature water-cooling cycles. The deformation, strength, and acoustic emission characteristics of sandstone were analyzed under different temperatures and cycle times. The results show that the high-temperature water-cooling effect caused changes in the physical properties of sandstone. The volumetric expansion rate of the rock samples first decreased, then increased in temperature, and the strength first increased, then decreased, whereas the number of cycles had less of an impact on the physical properties. At 200 °C, with increased cycle number, the elastic modulus increased by 20.1%, and the compressive strength increased from 63.9 MPa to 71.46 MPa. At 300–600 °C, the elastic modulus and compressive strength of sandstone gradually decreased with increases in the temperature and cycle number, with reductions of 6.04%, 7.24%, 28.7%, 35.57%, 17.6%, 18.2%, 20.4%, and 60.5%, respectively. With increased temperature and cycle times, the acoustic emission ringing counts increased, ringing counts and cumulative energy appeared earlier, the rock samples entered elastic deformation earlier, the yield stage length increased, and the samples showed a tendency to transition from brittle to ductile damage.

Effect of Physical Properties on Mechanical Behaviors of Sandstone under Uniaxial and Triaxial Compressions.

Mechanical properties of sandstone, such as compressive strength and young's modulus, are commonly used in the design of geotechnical structures and numerical simulation of underground reservoirs using models such as the digital groundwater, equivalent porous medium, and Discrete Fracture Network (DFN) models. A better understanding of the mechanical behaviors of sandstone under different loading conditions is imperative when assessing the stability of geotechnical structures. This paper highlights the effect of the physical properties (i.e., porosity, mean grain size) and environmental conditions (i.e., water content and confining stress) on uniaxial compressive strength, triaxial compressive strength, and young's modulus of sandstone. A series of uniaxial and triaxial compression experiments are conducted on sandstone formations from Wyoming. In addition, experimental data on sandstones from the literature are compiled and integrated into this study. Prediction equations for the compressive strengths and young's modulus of sandstone are established based on commonly available physical properties and known environmental conditions. The results show that the mean Uniaxial Compressive Strength (UCS) decreases as the porosity, water content, and mean grain size increase. Furthermore, a predictive empirical relationship for the triaxial compressive strength is established under different confinements and porosity. The relationship suggests that the mean peak compressive strength increases at a higher confinement and decreases at a higher porosity. The results and recommendations provide a useful framework for evaluating the strength and deformation of most sandstone.

Study on mechanical properties and fracture modes of sandstone with cracks under triaxial compression

AbstractThis study examines the mechanical properties and fracture modes of sandstone with single and double cracks under varying confining pressures through triaxial compression tests. The stress–strain curves, mechanical parameters, and fracture modes of both intact and cracked sandstone are analyzed based on experimental results. The study finds that the presence of cracks has a significant impact on the mechanical properties of sandstone, with greater damage observed with an increase in the number of cracks. The peak strength and strain of a cracked rock sample increase with the increase in crack angle. The fracture mode of sandstone is influenced by both crack angle and confining pressure. When the crack angle is small, the fracture mode is a combination of shear and tensile failure, while a large crack angle results in shear failure. Moreover, as the confining pressure increases, the degree of damage to the sandstone also increases.

Experimental investigation of temperature effects on the physical and mechanical properties of red sandstone

With the rapid development of transportation in China, the number of tunnels is also increasing. However, tunnels may be affected by fire accidents during operation, and the surrounding rock will be irreparably damaged by high temperature. To investigate the influence of temperature on the physical and mechanical properties of red sandstone, physical properties were determined and the Brazilian splitting test was conducted on red sandstone after thermal treatment from 25 to 600°C. The results show that with increasing temperature, the apparent colour of the red sandstone gradually deepened. The P-wave velocity and Leeb hardness decreased with increasing temperature, and a typical temperature threshold (300°C) was identified. The tensile strength of red sandstone decreased quickly from 25 to 300°C and then decreased slowly from 300 to 600°C. The acoustic emission (AE) signal shows a high degree of consistency with the stress–time curve. As the temperature increased, the AE became more active, and when red sandstone was near failure, the AE signal increased sharply. The failure mode of sandstone mainly consists of a throughgoing main crack and a secondary crack, and the crack width also grows gradually. Moreover, we observe from polarized light microscopy images that the number of fractures in the sandstone also increases as the temperature rises. The variation of physical and mechanical properties of red sandstone is closely related to microstructure. These findings demonstrate that temperature has an obvious weakening effect on the physical and mechanical properties of sandstone, and provide theoretical guidance and significant engineering information for tunnel fire restoration. Thematic collection: This article is part of the Engineering Geology and Hydrogeology of the Anthropocene collection available at: https://www.lyellcollection.org/topic/collections/engineering-geology-and-hydrogeology-of-the-anthropocene

Analysis of Acoustic Emission Energy Distribution and Avalanche Dynamics of Sandstone with Different Particle Sizes.

The mechanical properties of sandstone have an important impact on the stability of the coal mine roof and floor, sandstone gas mining, and underground engineering safety. In order to study the critical characteristics on the failure process of sandstone with different particle sizes under uniaxial compression conditions, avalanche dynamics theory and a critical model are used to analyze the distribution of acoustic emission (AE) parameters, and the maximum likelihood estimation is used to accurately estimate the critical parameters. The results showed that the AE phenomenon of sandstone can be divided into four stages: initial compaction period, quiet period, crack stable growth period and outbreak period. During the process of compression failure, the larger the particle size is, the more seriously the sandstone is damaged. The AE energy probability density distribution follows single power-law distribution, and the AE energy critical exponent is 1.20 and follows the characteristics of scale-free regarding the power-law distribution on the particle sizes. When the stress runs up to 90% of peak stress, the bifurcation ratio increases sharply and shows the characteristics of the critical state. The waiting time and the avalanche size distribution follow double power-law distribution, and the inflection points are 0.03 and 37. Before and after the inflection point, the waiting time critical exponent and the avalanche size critical exponent are 1.90, 0.40 and 2.40, 1.60. This shows that the dynamic evolution process of sandstone under uniaxial compression condition can be characterized well by the fiber bundle model.

Mechanical and fractal characteristics of sandstone with Pre-existing fissures of different lengths under varying impact loads in SHPB tests

The Split Hopkinson Pressure Bar (SHPB) with a 100 mm diameter was used to investigate the impact of pre-existing fissure length on the mechanical properties of sandstone under different launch pressure (P = 0.3 MPa, P = 0.45 MPa, and P = 0.6 MPa). Subsequently, CT scanning was conducted on sandstone samples with pre-existing fissure after failure to examine the relationship between pre-existing fissure length (Lc) and fractal characteristics under different launch pressures. Our findings indicate that, compared to intact sandstone, the proportion of plastic deformation in the stress–strain curve of sandstone with pre-existing fissure increases. As Lc increases, the initial plastic deformation stress and secant modulus decrease. After CT scanning, sandstone failure was classified into three conditions for different Lc: (1) Axial-splitting-tensile failure is caused by the development of natural defects, and in this case, the degree of development of pre-existing fissure is low, (2) Radial-splitting -tensile-failure is caused by the development of pre-existing fissure, in which the degree of development of pre-existing fissure is high and dominates the macroscopic failure of sandstone, while the degree of development of natural defects is low, and; (3) Combined-splitting-tensile failure: The failure of sandstone includes both axial-splitting-tensile failure and radial –splitting-tensile failure. At this time, both the degree of development of natural defects and pre-existing fissure are high, which jointly dominate the macroscopic failure of sandstone. With increasing launch pressure (P) and Lc, the failure mode of sandstone transitions from axial splitting-tensile failure to radial splitting-tensile failure, and eventually to combined splitting-tensile failure. However, local compression-shear failure occurs with increased launch pressure. Moreover, Lc significantly affects the fractal characteristics of sandstone. Under 0.3 MPa launch pressure, the fractal dimension (DH) on different height (H) slices initially increases and then decreases with increased Lc. Under 0.45 MPa launch pressure, the DH on different H slices exhibits two changes with increasing Lc. For H = 70 mm and H = 100 mm, the variation of DH is decreasing-increasing–decreasing-increasing, while for H = 0 mm and H = 30 mm, the variation of DH is increasing–decreasing-increasing. Under 0.6 MPa launch pressure, the DH on different H slices increases first and decreases secondly with the increase of Lc, but Lc is different when DH reaches its maximum.

Effects of Ultralow Temperature and Water Saturation on the Mechanical Properties of Sandstone

Effects of Ultralow Temperature and Water Saturation on the Mechanical Properties of Sandstone

Study on the Influence of Water Content on Mechanical Properties and Acoustic Emission Characteristics of Sandstone: Case Study from China Based on a Sandstone from the Nanyang Area

In order to study the influence of water content on the mechanical properties of sandstone and evolution of crack propagation, laboratory compression tests and Engineering Discrete Element Method (EDEM) numerical simulation of sandstone under different conditions were carried out by the RMT-150B rock mechanics test system. The sandstone samples were from Nanyang, Henan Province, containing a total of 12 rock samples. Under the confining pressure of 0, 5, 10, and 20 MPa, the rock samples with 0%, 1.81%, and 3.24% water content were tested. The findings demonstrated that as the sample’s water content grew, the peak strain increased but the peak strength, elastic modulus, maximum energy rate of individual acoustic emission events, and cumulative acoustic emission energy rate all reduced. While the ratio of tensile cracks to shear cracks inside the rock samples rose with increasing water content, the failure mode of sandstone changes from shear failure to tensile failure with the increase of water content, but the sandstone specimens in the three conditions exhibited shear macroscopic fracture surfaces. Research results will provide reference for the safe construction of underground projects in water rich areas.

Effects of Water and Cyclic Loading on Ultrasonic and Mechanical Properties of Sandstone: An Experimental Study

In this study, the water absorption, mechanical properties, and energy evolution characteristics of sandstone were examined through experimental and theoretical analysis. The P-wave velocity was found to initially decrease, then increased with immersion time and water content. The water absorption rates of three sandstone specimens decreased with immersion time and water content. The post-peak deformation of the sandstone changed from brittle failure to strain softening. With the increase in water content, the peak strength and loading Young’s modulus per cycle decreased. The loading Young’s modulus showed that the unloading stress and increment of unloading stress nonlinearly increased with the number of cycles and decreased before peak strength. With the increase in the number of cycles, residual strains of the sandstone specimens decreased slightly initially and then increased, while the elastic strains increased before peak strength and then decreased at the post-peak stage. With the increase in unloading stress, the energy densities nonlinearly increased. At the same unloading stress, an increase in water content led to an increase in the input energy density and energy ratios of the sandstone specimens.