Uniaxial Compression Creep Tests Research Articles

Experimental study on the mechanical properties of red sandstone with fractures under different loading rates

In order to study the effects of crack inclination angle and loading rate on rock mechanical properties, creep characteristics, and failure characteristics. Taking homogeneous red sandstone with different fracture angles as the research object, uniaxial compression tests and uniaxial compression creep tests were conducted at different loading rates. The results showed that under the same fracture angle, the loading rate was positively correlated with the peak strength, elastic modulus, instantaneous strain, creep strain, and steady-state creep rate of the sample, while negatively correlated with the peak strain. At the same loading rate, the mechanical properties and creep properties of the sample were controlled by the crack inclination angle α. With the increase of α, the peak strength, peak strain, instantaneous strain, creep strain and steady-state creep rate decreased first and then increased, and the elastic modulus increased. On the basis of rock creep testing, it is also important to establish a creep model that conforms to the actual test situation for studying rock creep characteristics. However, many models currently used cannot accurately describe the three stages of rock creep, especially the accelerated creep stage. Therefore, based on Burgers elements, this paper introduces plastic damage bodies based on damage rates and software components based on fractional calculus, A new creep model was obtained and its rationality was verified through experimental results. The results showed that the fit between the model and experimental data was above 0.97, indicating that the model can better describe the three stages of rock creep, especially reflecting the non-linear characteristics of the accelerated creep stage.

Deposition morphology and mechanical properties of lean cemented gangue backfill material: Laboratory test and field application

Backfilling mining technology provides an efficient and environmentally-friendly solution for treating additional products (such as tailings, coal gangue and other solid waste) in coal mining process, which are filled into the underground goaf area, thus reducing surface subsidence, roof strata damage, and associated geological disasters. In this study, a novel backfill material called lean cemented gangue backfill material (LCGBM) is introduced, and various experiments, including uniaxial compression tests, creep tests, CT-SEM scanning and reconstruction are carried out to evaluate its mechanical properties and engineering practicability. The test results indicate that the strength and volume fraction of self-compacting cement (SCC) slurry and solid waste aggregate jointly control the uniaxial compressive strength and failure mode of LCGBM, reflecting the bucket effect under the influence of two components. Although the volume fraction of aggregate and SCC slurry is intentionally reduced to control the cost, this cemented granular material shows excellent compressive strength, overall stiffness and long-term bearing capacity in laboratory and field tests. In the process of engineering application, the uniaxial compressive strength of the LCGBM reaches 14 MPa, and the initial setting time is 120 s, which reduces the consumption of gangue aggregate by 35 % and greatly reduces the construction time. In addition, a calculation method of the optimal mixing ratio of raw materials is proposed, which can adjust the strength and volume fraction of SCC slurry according to the optimal mixing range, so as to maximize the utilization of the strength of LCGBM, and reduce the construction time and aggregate of backfilling. The research findings emphasize the potential of the LCGBM in promoting clean and sustainable coal mining practice.

Experimental study on the creep acoustic emission of fractured sandstone reinforced by anchor rods

To investigate the reinforcement and crack-stopping effect of anchor rods on fractured rock masses, Triassic sandstone from the Xiaolangdi Reservoir area was selected and fabricated into double-fractured specimens. Subsequently, 1 and 2 horizontal anchor rods were used to reinforce the double-fractured sandstone specimens sequentially. Using the RLJW-2000 rock rheological servo tester and the PCI-II type acoustic emission (AE) tester, indoor uniaxial compression creep and AE tests were conducted under the same experimental conditions for the unanchored, singly-anchored, and doubly-anchored sandstone specimens. Based on the experimental results, the creep mechanical characteristics and the three-dimensional spatial evolution of the AE events of the specimens with different numbers of anchor rods were analysed. This study focuses on the reinforcement and crack-stopping effect of anchor rods on fractured rock masses. The experimental results indicate the following: (1) Compared with those of the unanchored specimens, the creep failure strengths of the singly- and doubly-anchored specimens increase by 7.79 % and 22.14 %, respectively. (2) At a stress level of 60 MPa, the axial strains of the single-anchor and double-anchor specimens decreased by 8.41 % and 32.97 %, respectively, compared to the corresponding strain of the unanchored specimen, and the radial strains decreased by 9.21 % and 28.13 %, respectively. (3) Anchor rods have a good reinforcement effect on fractured sandstone, enhancing specimen strength and reducing deformation. (4) With an increase in the number of anchor rods, the reinforcement effect of anchor rods on fractured rock masses strengthened, and the reinforcement effect of double anchors was superior to that of single anchors. (5) Compared with those of the unanchored specimens, under relatively low stress levels, when the AE events extended to the area where the anchor rods were located, the number of AE events for both types of specimens decreased significantly, forming a blank area in the AE events, and the blank area of the double-anchored specimens was larger than that of the single-anchored specimens. (6) With increasing stress, many AE events originated, expanded, and passed through the anchor rod area, indicating that the specimen was about to undergo creep instability failure. (7) The evolution characteristics of the AE events are in good agreement with those of the macroscopic cracks on the specimen surface. The AE characteristics indicate that anchor rods have a significant crack-stopping effect on fractured rock masses, suppressing the initiation, expansion, connection, and penetration of internal microcracks in the specimens. Moreover, the crack-stopping effect of double anchors is superior to that of single anchors.

Simulation method of asphalt mixture based on fracturable digital aggregate model

This study proposed an approach to construct a fracturable aggregate model to make the fracture patterns consistent with the real situation. Firstly, this study utilized three-dimensional structured light technology to obtain the geometric shell of aggregate and divide them into four categories of spherical, angular, elongated and flaky aggregates according to the minimum bounding box algorithm. Secondly, this study proposed a discrete-spheres filling algorithm based on the Bubble Pack Filling algorithm to fill the shell accurately. Thirdly, this study established the conversion equations between the macro and micro parameters of aggregate by using the linear parallel bonding model, and used it to establish the fracturable aggregate model. Through the indoor and virtual static fracture tests, this study found that the fracture patterns of the fracturable aggregate models are similar to the real situation and characterized the fracture patterns of four types of aggregates. Further analyzing the virtual static fracture tests, this study found that the bearing capacity of aggregates is determined by the compressive strength of host rocks and the shape of aggregate. Through the indoor and virtual uniaxial compression creep tests, this study investigated the behavior of the mixture specimens consisted by the fracturable aggregate model. The stress-strain curves of the fracturable and unfracturable aggregate model in this test were plotted in this study, and the results showed that the relative error between the results obtained by the fracturable model and those of the indoor test is much smaller than that of the unfracturable model. Considering that existing simulation tests on asphalt mixture often ignore aggregate deformation and fracture, so this study used the method mentioned above to obtain the fracturable aggregate model, which can improve the confidence of asphalt mixture simulation results.

Uniaxial compressive creep tests by spark plasma sintering of 70% theoretical density α-uranium and U-10Zr

Metallic fuels hold numerous advantages over conventional uranium dioxide fuels and are a key component of several liquid metal-cooled advanced reactor concepts including sodium fast reactors. These fuels undergo rapid swelling during early burnup; consequently, they spend most of their reactor lifetime in a porous state. The presence of this porosity alters many of the mechanical properties of the fuel including creep impacting fuel deformation during axial swelling. This work investigates the creep behavior of the porous fuel using a spark plasma sintering technique. Creep tests were performed for the first time on porous α-phase uranium and uranium with 10 wt. % zirconium (U-10Zr) samples. The samples of α-phase uranium and U-10Zr were fabricated from depleted uranium by spark plasma sintering and subjected to uniaxial compressive creep testing. Calculated stress exponents were found to be 2.6±1.6 and 5.7±1.4 for α-U and U-10Zr, respectively, and calculated activation energies were found to be 61.6±1.1kJ/mol for α-U. The creep data were also used to evaluate existing porosity inclusive in creep models.

Experimental study on I/II/III mixed mode fracture characteristics of a combined rock mass under creep loading

I/II/III mixed mode fractures of intersecting joint fissures often occur in natural rock masses, and jointed rock masses are prone to rockbursts in deep underground engineering when subjected to long-term crustal stresses. However, most studies of the mechanical mechanisms of these intersected joints have been conducted by simplifying two-dimensional joint model tests. Furthermore, the fracture mechanisms of two-dimensional intersected joints under tension and compression are completely different from those of three-dimensional joints. This paper presents a novel prefabricated specimen with combinations of intersecting joints capable of detecting the failure behaviours of rock I/II/III mixed mode fractures under creep loading. Uniaxial compression and multistage creep tests are performed on prefabricated sandstone specimens with intersecting joints of 0°/0°, 0°/30°, 0°/60°, and 0°/90°. The experimental results show that with the increase in the number of prefabricated intersecting joints, the uniaxial compressive strength and elastic modulus values of the sandstone specimens gradually decrease. In addition, the sandstone specimens experience relatively few AE events and minor axial strain variations in the first creep stage and the second creep stage of the multistage creep test. The axial strain increases sharply due to the sharp increase in the number of AE events in the third creep stage. The 0°/60° sandstone specimen undergoes accelerated creep failure, resulting in mixed X-shaped tensile‒shear rupture. The RA value is high based on the quantification of the creeping cracks using the acoustic emission parameters of the rise angle (RA) and average frequency (AF). The AF values of the 0°/0°, 0°/30°, and 0°/90° sandstone specimens are high. The experimental results show that a larger joint intersection angle leads to greater mutual restraints and greater effects of prefabricated crack propagation in the rock specimens, thus increasing the final failure strength. Finally, based on the acoustic emission count, a characteristic variable D suitable for characterizing the creep damage evolution of a joint rock mass is established. The findings of this paper can facilitate an effective understanding of the creep effect of I/II/III mixed mode fracture and its micromechanism. The research results will have a certain reference value for the detection and risk mitigation of instantaneous and time-delayed rockbursts.

Investigation of the influence of pre-crack number on acoustic emission characterization of red-sandstone short-term creep damage and failure precursors

Rock crack is one of the main factors responsible for rock failure. Uniaxial compression creep tests are performed using acoustic emission techniques, a high-sensitivity, non-radiative, non-destructive testing method to understand the influence of crack number on the precursor characteristics of short-term creep damage in the fractured rock mass. Based on the Grassberger-Procaccia (G-P) algorithm, the calculation step size for the correlation dimension value (D 2) of the acoustic emission ringing count rate is consistent with that for the acoustic emission b-value. The influence of the number of pre-cracks on the Acoustic emission precursor characteristics of red sandstone creep is analyzed. The results show that near the destabilization of the specimen, the Acoustic emission accumulative ringing count surges in a stepwise manner, the Acoustic emission b-value decreases, the D 2-value increases, the Acoustic emission amplitude shows high intensity and high frequency, and the ringing count increases sharply, all with the characteristics of failure precursors. During the accelerated creep stage of the specimens, with the increase of pre-cracks number, the precursory time points of acoustic emission b-value and D 2-value advance, and their acoustic emission ringing counts increase sharply.

Effect of Cyclic Loading Treatment on the Compression Energy and Creep Properties of Machine-Harvested Seed Cotton

Machine-harvested seed cotton was taken as the research object to further clarify its creep performance, minimize its power consumption during the loading process, and obtain a better loading method. The uniaxial compression creep test was carried out using the Instron universal material test bench to apply cyclic loading treatment. The test factors included cyclic loading times, cyclic stress peak, and cyclic loading frequency. The energy consumption curve of the machine-harvested seed cotton during cyclic loading was obtained through OriginPro 2019b software, and its energy change law was analyzed. Creep strain was divided into two parts, namely, initial creep strain and creep strain increment, to elucidate the creep mechanism. The Burgers model was chosen to describe the creep strain increment. Results show that machine-harvested seed cotton exhibits energy consumption hysteresis during cyclic loading. The compression energy rapidly decreases with increasing cyclic loading times and then stabilizes. Meanwhile, the compression energy increases with increasing cyclic stress peak and cyclic loading frequency. The creep strain mechanism is also the same, which first rapidly increases and then levels off. Cyclic loading times, cyclic stress peak, and cyclic loading frequency have different effects on creep strain increment, instantaneous elastic modulus, hysteresis elastic modulus, viscosity coefficient, delay time, and relative deformation index. Finally, disregarding power consumption and interaction, extending the cyclic loading time, and increasing the cyclic stress peak while simultaneously minimizing the cyclic loading frequency can reduce the relative deformation index in the creeping stage. Accordingly, the deformation retention ability in the creep is improved, but the compression energy in the cyclic loading increases. The results can provide theoretical and data support for studying the theoretical basis of the rheological properties of machine-harvested seed cotton, the design of seed cotton baling devices, and the study of bale (mold) forming quality.

Investigation into the Long-Term Stability of Carnallite Pillars Considering Creep Influence

Abstract In subterranean potash mines utilizing the room-and-pillar mining method, maintaining the long-term stability of carnallite pillars is imperative for the safety and ongoing viability of operations. This study undertakes uniaxial compression creep tests on carnallite samples sourced from the Dongtai Potash and Magnesium Salt Mine in Laos. The durability of carnallite pillars is evaluated using an advanced Burgers creep model combined with Flac3D numerical simulations. Results indicate that the creep strength of carnallite is approximately 60%–70% of its immediate strength, demonstrating significant creep behavior. The refined Burgers model provides an accurate representation of the carnallite’s creep characteristics. Post-excavation, the internal compressive stress within the pillars progressively increases, registering an approximate rise of 1 MPa, and stabilizes under pressure after one year. After three years of continuous observation through creep tests and Flac3D simulations, the maximum deformations detected in the roof and floor of the mining house, as well as the adjacent rock masses, were 60mm and 20mm, respectively, indicating minimal overall deformation. The width of the plastic zone within the pillars exhibits time-dependent growth, with rapid expansion occurring in the internal plastic zone and a significant deformation rate within the first six months post-excavation. To ensure the long-term stability of the mining pillars and voids, it is recommended that backfilling operations be conducted within six months following the excavation.

Experimental and Numerical Study of Water–Rock Coupling Creep under Uniaxial Compression

In order to study the influence of the long-term strength of the rock surrounding deep roadways under the action of groundwater on surrounding rock stability, taking the rock surrounding the deep roadway of the Wanfu Coal Mine as the main research object, uniaxial compression and uniaxial creep tests were carried out on sandstone samples under different water-content states. It was found that the water content had an obvious softening effect on short-term and long-term strength, and both strengths showed a negative exponentially declining relationship. The viscosity modulus (E¯v) was put forward to describe viscoelastic creep deformation. And damage variables corresponding to E (the instantaneous elastic modulus) and E¯v were proposed. A sticky element that can describe the accelerated creep behavior was also established to improve the Nishihara model, based on the experimental results and damage theory. A comparison of the identified parameters and the experimental curves showed that the model can describe the mechanical behavior of various creep stages well. The model was developed using the ABAQUS user subroutine function, and the uniaxial compression creep experiment was simulated. The simulation results were basically consistent with the experimental results, which provide a basis for the further long-term stable use of roadway and creep failure simulation and have important practical and guiding significance.

Effects of Initial Damage on Time-Dependent Behavior of Sandstone in Uniaxial Compressive Creep Test

Effects of Initial Damage on Time-Dependent Behavior of Sandstone in Uniaxial Compressive Creep Test

Creep Behavior of CLT Beams with Finite Thickness Layers of Flexible Adhesives.

Creep behavior of Cross-Laminated-Timber (CLT) beams with a finite-thickness layer of flexible adhesives is investigated. Creep tests were carried out for all component materials as well as for the composite structure itself. Three-point bending creep tests were performed for spruce planks and for CLT beams, and uniaxial compression creep tests were performed for two flexible polyurethane adhesives: Sika® PS and Sika® PMM. All materials are characterized with the use of the three-element Generalized Maxwell Model. The results of creep tests for component materials were used in elaboration of the Finite Element (FE) model. The problem of linear theory of viscoelasticity was solved numerically with the use of the Abaqus software. Obtained results of Finite Element Analysis (FEA) are compared with experimental results.

High temperature creep behavior of fireclay refractory and its masonry

The creep behavior of refractory lining is crucial, which is determined by both material and masonry structure. In this paper, the effect of temperature and stress on the creep behavior of fireclay refractory and brick–mortar couplets were studied by using advanced uniaxial compression creep test. The creep behavior of fireclay refractory is sensitive to temperature due to formation of liquid phase. Meanwhile, the closure of discontinuous interfaces contributes to the increase of compressive creep in couplets. The masonry specimen with two mortar layers deforms less than that with one mortar layer, as thermal stresses are moderated by the additional mortar layer.

Investigating time-dependent behavior of rocks using kinematic-constraint-inspired non-ordinary state-based peridynamics

In this paper, the kinematic-constraint-inspired non-ordinary state-based peridynamic formulation (KC-NOSBPD) is proposed to investigate the time-dependent behaviors of rocks, which play a critical role in evaluating the long-term stability of the surrounding rocks around underground opening quantitatively. The peridynamic differential operator (PDDO) is introduced to KC-NOSBPD to improve the precision of bond-associated deformation gradient and to suppress the skin effect. On this basis, a unified creep-damage-rupture KC-NOSBPD model is proposed, in which the Burgers-creep viscoplastic constitutive law, a visco-elastoplastic constitutive model, is used to describe the rheological deformation of rocks. A unified damage-rupture framework based on a strain-based isotropic scalar damage variable is established to simulate the creep damage and subsequent creep rupture. The fidelity of this proposed model without damage is verified by comparing it with the benchmark solution for the creep response of a 2D rock specimen subjected to various load histories. Further, the proposed model is employed to simulate uniaxial and triaxial compression creep tests. These present numerical results agree well with the experimental observation, implying that the proposed model successfully captures the accelerating creep behavior of rocks. Moreover, the proposed model performs the time-dependent deformation and failure analysis for the surrounding rocks around the tunnel.

Creep damage coupling model of concrete based on the statistical damage theory

The creep behavior is one of the key issues in the design and construction of hydraulic concrete structures. However, it is an enormous challenge to accurately predict the development of creep deformation in concrete structures. Since the creep deformation behavior of concrete under long-term load action originates from the interaction between creep and damage, a new creep damage coupling model was developed by introducing the damage variable into the creep constitutive equation. This model utilized the statistical damage theory framework and assumed that the damage variable follows the random distribution described by the Weibull function. Then Weibull distribution parameters F0 and m were derived to determine the evolution equation of the damage variable D. Considering stress under complex stress conditions may change, the stress-strain correlation of concrete under complex stress conditions was deduced using the elastic creep theory. Moreover, the results of uniaxial compressive concrete creep tests with the corresponding numerical simulations under different levels of sustained loads, and the accuracy and applicability of the creep damage coupling model were verified. Consequently, the nonlinear creep properties of hydraulic concrete were analyzed by combining it with acoustic emission techniques.

Transversely isotropic creep characteristics and damage mechanism of layered phyllite under uniaxial compression creep test and its application

Transversely isotropic creep characteristics and damage mechanism of layered phyllite under uniaxial compression creep test and its application

Effects of supercritical CO2 on viscoelastic properties of shales

Laboratory uniaxial compression creep tests, with differential stress of 30 MPa hold for 3 h, were performed on Chang-7, Longmaxi (LMX) and Barnett shales to study the influence of SC-CO 2 on short-term viscoelastic properties. To this end, the wet shale samples were treated with SC-CO 2 with a pressure of 30 MPa and a temperature of 110 °C for 14 days. We analyzed the creep data using the fractional Maxwell model. To investigate microscopic structural alterations, the surface morphology of the same location, before and after SC-CO 2 -water exposure, was examined by SEM images. Compared with dry shales, dynamic and static elastic moduli decreased by up to 25.02% and 55.83%, respectively, but the creep deformation increased by 200% for LMX and Chang-7 shales, and 500% for the Barnett shale treated by SC-CO 2 . Compared to dry sample, there is an increase in calculated fractional orders of 0.02, 0.07, 0.22 for SC-CO 2 treated samples, indicating that SC-CO 2 treatment is likely to enhance shale creep. SEM investigation confirmed physicochemical mechanisms responsible for the observed elastic damage and creep enhancement, including mineral dissolution and swelling caused by SC-CO 2 . This work would further improve our current understanding of the time-dependent deformation of shale under chemical-mechanical coupling effects during CO 2 capture utilization and storage.

Model test research on creep characteristics of discontinuous structural surfaces slope

The rock slopes in nature are mainly cut by joints, which are in a non-persistent state in the rock mass. The creep mechanical characteristics of discontinuous structural surfaces have a significant and complicated influence on slope stability. Based on the analysis of the characteristics of a rock slope in Western Hubei before and after instability, the geological prototype of the slope is generalized, and the mechanical model of the discontinuous structural surfaces is established. Based on the uniaxial compression creep test, the phase creep characteristics of discontinuous structural surfaces are analyzed. The instantaneous strain in the creep process of discontinuous structural surfaces decreases greatly, and then increases slowly. The creep strain increases with the increase of stress. A viscoelastic-viscoplastic element that can describe the viscoelastic and the viscoplastic properties and damage variables are introduced, and an improved Nishihara damage creep constitutive model is constructed. The Levenberg-Marquardt (L-M) algorithm and global optimization method are used to verify the improved Nishihara damage constitutive model. After verification, comparing the experimental values and the predicted values of the damage constitutive model, the results show that the improved Nishihara damage constitutive model can better simulate the creep process of discontinuous structural surfaces. The author hopes that this study can provide reference for the study of creep characteristics of discontinuous structural surfaces in the future.

Creep Properties of Mudstone Interlayer in Bedded Salt Rock Energy Storage Based on Multistage Creep Test: A Case Study of Huai’an Salt Mine, Jiangsu Province

Salt rock is internationally recognized as an excellent medium for energy storage. However, most of the domestic salt mines are lacustrine laminated formations with mudstone interlayers, which have different creep characteristics to pure salt rocks. Therefore, in this paper, uniaxial compression creep tests were carried out on a mudstone interlayer in Huai’an, Jiangsu, China, and the multistage creep mechanical behavior of the mudstone interlayer was investigated using acoustic emission (AE) technology. The results show that at low stress levels, the axial deformation of the interlayer is greater than the lateral deformation. As the increase of the stress level, the lateral deformation becomes more significant, and the corresponding axial and lateral steady-state creep rates both exhibit nonlinear acceleration with the increase of the loading stress. In the initial loading stage of each stress level, the mudstone interlayer releases a large number of AE signals. After the creep stabilization, the AE signals decreased obviously, and a large number of AE signals were released at the last stress level. Based on the creep test data, an improved fractional viscoelastic-plastic model was fitted to it and compared with the Nishihara model. The applicability of the model was also tested, and the model was found to be a good description of the mudstone interlayer after oil erosion. The research results reflected the creep law of the mudstone interlayer to a certain extent and are expected to serve as a reference to studies on the long-term stability of the surrounding rock of a bedded salt rock energy storage.

Study on Creep Mechanical Properties of Non-Water Reacting Polyurethane Grouting Material

Non-water reacting polyurethane is a new type of grouting material for support reinforcement and emergency rescue, whose creep mechanical behavior is directly related to the stability and safety of the reinforcement project. To investigate the creep properties of non-water reacting polyurethane grouting material, a series of multistage loading creep tests were performed under uniaxial compression conditions. Then, the creep curves, creep strain rate, and creep failure modes of non-water reacting polyurethane grouting material were obtained. In addition, the effects of temperature and density on the creep properties of non-water reacting polyurethane grouting material were also analyzed. Finally, based on the finite difference program, the numerical simulation of the uniaxial compression creep test of non-water reacting polyurethane grouting material was conducted by employing the Burgers–Mohr creep model. The simulated creep curve was in good agreement with the test curve, which verified the feasibility of the model to describe the creep characteristics of non-water reacting polyurethane grouting material. The research results can provide a reference for studying the creep behavior of polyurethane grouting material and also contribute to the development and application of polyurethane material grouting technology.