Triaxial Conditions Research Articles

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.

Evaluating the Long-Term Plastic Strain Accumulation in Reclaimed Asphalt Pavement (RAP) Application for Road Subbase Construction: A Cyclic Triaxial Loading Study

Reclaimed Asphalt Pavement (RAP) has gained significant attention in recent years as an environmentally sustainable solution for road construction. However, the main concerns are regarding its long-term performance and the potential impact on the road subbase. This study aims to investigate the behavior of RAP under cyclic triaxial loading conditions, specifically focusing on the accumulation of plastic strain over time. The research methodology involved laboratory testing using a cyclic triaxial apparatus to simulate the stress conditions experienced by RAP in road subbase applications in reference to AASHTO code. Several RAP specimens with varying degrees of compaction were subjected to repeated cyclic loading while monitoring the associated plastic strain accumulation. To provide a comparative analysis, conventional subbase materials were also tested under the same conditions. The findings indicate that RAP exhibits a notable disadvantage in terms of long-term plastic strain accumulation when compared to conventional subbase materials. The cyclic triaxial loading tests revealed a substantial increase in plastic strain accumulation over extended periods, suggesting the potential for long-term deformations and compromised performance of the road structure. This accumulation of plastic strain could lead to increased maintenance requirements and decreased service life of the road. Based on the results obtained, it is recommended that careful consideration be given to the utilization of RAP in road subbase construction in areas subjected to heavy cyclic loading conditions. Additional research and development efforts are necessary to explore potential mitigation strategies and optimize the use of RAP, ensuring sustainable and resilient road infrastructure.

Brittleness index evaluation of gas-bearing sandstone under triaxial compression conditions

Brittleness is a critical property in gas-bearing rock excavation and reservoir fracturing. This paper analyzes the three types of brittleness indices in detail, proposes new indices, and conducts relevant conventional triaxial tests for analysis. A stress–strain curve-based brittleness index would be appropriate for the evaluation of brittleness if the parameters represented unique and certain stress–strain curves. Therefore, a new brittleness index is proposed. It consists of two components: the stress variation index and the strain variation index, which reflects the strain ratio of the stress drop and the relationship between elastic and post-peak strains, combining the stress variation and strain variation in the pre- and post-peak phases. Triaxial compression tests of sandstone under different confining pressures and gas pressures were conducted, and specific stress and strain parameters were collected. Based on the comparison and analysis of various brittleness indices, it is found that the newly proposed brittleness index can be a good measure of the brittle evolution of sandstones under different confining pressures and gas pressures, and it can provide a more accurate estimate of rock brittleness than the existing indices. The index is also used to further investigate the relationship between rock brittleness and confining and gas pressures. This has important implications for the assessment of rock brittleness in practical engineering.

A multifunctional shear apparatus for rocks subjected to true triaxial stress and high temperature in real-time

Deep engineering disasters, such as rockbursts and collapses, are more related to the shear slip of rock joints. A novel multifunctional device was developed to study the shear failure mechanism in rocks. Using this device, the complete shear–deformation process and long-term shear creep tests could be performed on rocks under constant normal stiffness (CNS) or constant normal loading (CNL) conditions in real-time at high temperature and true-triaxial stress. During the research and development process, five key technologies were successfully broken through: (1) the ability to perform true-triaxial compression–shear loading tests on rock samples with high stiffness; (2) a shear box with ultra-low friction throughout the entire stress space of the rock sample during loading; (3) a control system capable of maintaining high stress for a long time and responding rapidly to the brittle fracture of a rock sample as well; (4) a refined ability to measure the volumetric deformation of rock samples subjected to true triaxial shearing; and (5) a heating system capable of maintaining uniform heating of the rock sample over a long time. By developing these technologies, loading under high true triaxial stress conditions was realized. The apparatus has a maximum normal stiffness of 1000 GPa/m and a maximum operating temperature of 300 °C. The differences in the surface temperature of the sample are constant to within ±5 °C. Five types of true triaxial shear tests were conducted on homogeneous sandstone to verify that the apparatus has good performance and reliability. The results show that temperature, lateral stress, normal stress and time influence the shear deformation, failure mode and strength of the sandstone. The novel apparatus can be reliably used to conduct true-triaxial shear tests on rocks subjected to high temperatures and stress.

Experimental study on the failure characteristic and mechanism of granite time-delayed rockburst under true triaxial condition

A series of tests for time-delayed rockburst of granite under true triaxial condition was designed and carried out. By using the true triaxial rockburst test system, an acoustic emission (AE) system, a high-speed camera system, and a digital image motion analysis software, the time-delayed rockburst development process was monitored and studied. Four stages were found in the failure of granite time-delayed rockburst, i.e. grains ejection, slab breaks and ejects, first fragments ejection and second fragments ejection. There is a “V” shear crack generated in the time-delayed rockburst sample, and several tensile cracks in the lower part of the rock sample cross through the “V” shear crack. The longer the duration (the time elapsed between the moments the AE hits rises rapidly and the rockburst occurs), the smaller the depth of the rockburst pit. The time-delayed rockburst debris are mainly composed of blocks and fragments. The longer the duration, the smaller the total debris mass, the percentage of ejected debris and the ejection kinetic energy. The fractal dimension of the debris is positively correlated with the duration. The longer the duration, the higher the degree of fragmentation. The cracks generated are tensile-shear composite cracks. In the loading stage, it is dominated by shear cracks. However, in the time-lag stage, it is dominated by tensile cracks. With the increase of the duration, the proportion of tensile cracks increased and the proportion of shear cracks decreased. The research results will have a certain reference value for the warning and risk mitigation of time-delayed rockbursts.

Investigation of Small Strain Dynamics in Modified Aeolian Sand under Vibration Triaxial Conditions

By utilizing vibration triaxial tests, this study analyzed the effects of various factors, such as confining pressure, consolidation ratio, and silt content on the elastic modulus and damping ratio of silt-modified aeolian sand under conditions of minor deformation. The results indicate that with increasing confining pressure and consolidation ratio, the dynamic elastic modulus of improved aeolian sand gradually increases, while the damping ratio decreases progressively. The dynamic elastic modulus growth rate of untreated aeolian sand demonstrates a positive correlation with confining pressure, while the corresponding rate for the modified aeolian sand by adding cement and silt exhibits an inverse correlation with confining pressure. As dynamic strain increases, the dynamic elastic modulus decreases and approaches a stable value. The damping ratio rises at a diminishing rate and eventually stabilizes as dynamic strain continues to increase. The dynamic stress-strain backbone curve of the modified aeolian sand follows a theoretical hyperbolic model, while the small strain dynamic behavior is consistent with the Hardin-Drnevich model.

A new damage constitutive model for frozen-thawed sandstone under triaxial conditions: Considering the characteristics of pre-peak compaction and post-peak residual strength

The study of the constitutive model under stress loading for rock after undergoing freeze-thaw weathering cycles (FTWCs) treatment has important theoretical significance for the site operation and numerical calculation of rock mass engineering in cold regions. In this work, a series of FTWCs treatment tests of sandstone were carried out, and the evolution characteristics of the T2 spectrum distribution curve for sandstone before and after FTWCs treatment were analyzed utilizing nuclear magnetic resonance (NMR) technology. The schematic diagram of freeze-thaw damage evolution for sandstone was drawn, and the damage evolution mechanism was analyzed. Evolution laws of the stress-strain curves, peak and residual strength, peak and residual strain, and Young's modulus of sandstone under different FTWCs and confining pressures were analyzed by conventional triaxial compression tests. A piecewise constitutive model under triaxial stress loading for sandstone after undergoing FTWCs treatment was established, and the model considered the significant influence of FTWCs on the nonlinear deformation in the compaction stage and residual strength. By introducing error analysis indexes, the proposed model and published models were compared with the experimental data, it was found that the proposed model's performance is better than the published models, which indicated that the proposed model has good performance and strong universality.

A conceptual three-dimensional frictional model to predict the effect of the intermediate principal stress based on the Mohr-Coulomb and Hoek-Brown failure criteria

The intermediate effective principal stress has a considerable influence on rock strength as shown by true-triaxial data on intact rock. Therefore, a failure criterion that incorporates all three principal stresses may provide an improved prediction of failure than one that considers only the major and minor effective principal stresses. This study introduces a generalisation method, which converts two-dimensional failure criteria (i.e., Mohr-Coulomb and Hoek-Brown failure criteria) to three-dimensional failure criteria, for the prediction of this true-triaxial data. This method is based on a physical mechanism, and it assumes that the potential failure surface of a material has roughness, which provides additional frictional resistance when the intermediate effective principal stress is greater than the minor effective principal stress. This roughness is introduced theoretically by assuming a repeating diamond-shaped element over the failure surface. These roughness elements have the same dip as predicted by the Mohr-Coulomb and Hoek-Brown failure criteria but are offset by the dip direction angle which is assumed similar to that calculated traditionally from the major effective principal stress direction to the failure surface. With this roughness, it is shown that the major effective principal stress at failure can be predicted using an explicit solution that uses the intermediate and minor effective principal stresses and the Mohr-Coulomb or Hoek-Brown parameters as inputs. This generalisation predicts the same strength as the Mohr-Coulomb or Hoek-Brown failure criteria under conventional triaxial loading conditions, when the intermediate and minor effective principal stresses are equal. Under general stress conditions, this generalisation produces results that are aligned closely with the true-triaxial data as well as other previous theoretical predictions. This method importantly gives a possible physical mechanism for the strengthening influence of the intermediate effective principal stress. This may lead to a more accurate prediction of the rock strength under general stress conditions.

New geometry-inspired numerical convex analysis method for yield functions under isotropic and anisotropic hardenings

Convexity of a yield function must be guaranteed to ensure unique relationship between plastic strain increments and stress components. A geometry-inspired numerical convex analysis (GINCA) approach is developed to analyze the convexity of a yield function. The numerical approach is verified by the computation of convex domains for several typical yield functions of Drucker, Cazacu-Barlat2004, Hu2017, Cazacu2018 and a newly proposed function for differential-anisotropic hardening. The verified GINCA is applied to analyze the convexity of the Gao2011 yield function since it was not determined yet. The numerical approach is also used to determine the convex domain evolution with respect to plastic deformation in an anisotropic hardening function. It is also applied to investigate the convexity of polynomial yield functions for strong anisotropic metals. The result shows that the GINCA can effectively and correctly compute the convex domain for different yield functions. Besides, the numerical approach only needs to compute the effective stress from a yield function without any computation of the first- and second-order partial derivatives, compared to the complicated convex analysis by the Hessian matrix. Therefore, the proposed GINCA is user-friendly, effective and accurate to analyze the convexity of a yield function both for isotropic hardening and anisotropic/differential hardening. The Matlab codes are shared as electric attachments for scientists and engineers to check the convexity of a yield surface under biaxial loading, plane stress with shear stress and triaxial loading conditions.

Mechanical and Microstructural Response of Iron Ore Tailings under Low and High Pressures Considering a Wide Range of Molding Characteristics

The dry stacking of filtered tailings is an option to deal with safety-related issues involving traditional slurry disposition in impoundments. Filtered tailings can be compacted to pre-define design specifications, which minimizes structural instability problems, such as those related to liquefaction. Yet, comprehending the tailing’s response under various stress states is essential to designing any dry stacking facility properly. Thus, the present research evaluated the mechanical response of cemented and uncemented compacted filtered iron ore tailings, considering different molding characteristics related to compaction degree and molding moisture content. Therefore, a series of one-dimensional compression tests and consolidated isotropically drained triaxial tests (CID), using 300 kPa and 3000 kPa effective confining pressures, were carried out for different specimens compacted at various molding characteristics. In addition, changes in gradation owing to both compression and shearing were evaluated using sedimentation with scanning electron microscope tests. The overall results have indicated that the 3% Portland cement addition enhanced the strength and stiffness of the compacted iron ore tailings, considering the lower confining pressure. Nevertheless, the same was not evidenced for the higher confining stress. Moreover, the dry-side molded specimens were initially stiffer, and significant particle breakage did not occur owing to one-dimensional compression but only due to shearing (triaxial condition).

Failure characterization of fully grouted rock bolts under triaxial testing

Confining stresses serve as a pivotal determinant in shaping the behavior of grouted rock bolts. Nonetheless, prior investigations have oversimplified the three-dimensional stress state, primarily assuming hydrostatic stress conditions. Under these conditions, it is assumed that the intermediate principal stress (σ2) equals the minimum principal stress (σ3). This assumption overlooks the potential variations in magnitudes of in situ stress conditions along all three directions near an underground opening where a rock bolt is installed. In this study, a series of push tests was meticulously conducted under triaxial conditions. These tests involved applying non-uniform confining stresses (σ2 ≠ σ3) to cubic specimens, aiming to unveil the previously overlooked influence of intermediate principal stresses on the strength properties of rock bolts. The results show that as the confining stresses increase from zero to higher levels, the pre-failure behavior changes from linear to nonlinear forms, resulting in an increase in initial stiffness from 2.08 kN/mm to 32.51 kN/mm. The load-displacement curves further illuminate distinct post-failure behavior at elevated levels of confining stresses, characterized by enhanced stiffness. Notably, the peak load capacity ranged from 27.9 kN to 46.5 kN as confining stresses advanced from σ2 = σ3 = 0 to σ2 = 20 MPa and σ3 = 10 MPa. Additionally, the outcomes highlight an influence of confining stress on the lateral deformation of samples. Lower levels of confinement prompt overall dilation in lateral deformation, while higher confinements maintain a state of shrinkage. Furthermore, diverse failure modes have been identified, intricately tied to the arrangement of confining stresses. Lower confinements tend to induce a splitting mode of failure, whereas higher loads bring about a shift towards a pure interfacial shear-off and shear-crushed failure mechanism.

Soil–Geosynthetic Interaction Under Triaxial Conditions: Shear Strength Increase and Influence of the Specimen Dimensions

Geosynthetics are extensible reinforcements used to enhance the engineering performance of a soil. The transfer of stresses from the soil to the reinforcement is achieved through soil–geosynthetic interaction. The proposals from the literature to assess the shear strength of the reinforced soil under triaxial conditions use three different approaches. These involve analysing the reinforced soil: (i) as a homogeneous composite material (Approach A), (ii) as two different materials (Approach B), or (iii) as soil having the same fundamental shear strength, with the effect of the reinforcement represented as an additional lateral or confining stress (Approach C). In this paper, triaxial tests data of a soil reinforced with a geosynthetic, and specimens with different dimensions (diameters 70 and 150 mm) were used to assess changes in shear strength and to carry out a statistical analysis. The increases in shear strength of the reinforced soil and of the soil–geosynthetic interface were analysed using equations from the literature. The difference between the triaxial results obtained from specimens of different sizes was assessed using an Analysis of Covariance (ANCOVA). When the joint term of the regression model was not statistically significant, the characterisation from different specimen sizes was used to generate soil failure envelopes. Thus, a new methodology to obtain a failure envelope with different specimen sizes is presented.

Reactivation of variably sealed joints and permeability enhancement in geothermal reservoir rocks.

The online version contains supplementary material available at 10.1186/s40517-023-00271-5.

Space-time evolution characteristics of loaded gas-bearing coal fractures based on industrial μCT

Abstract The space-time evolution characteristics of fractures in coal seams under external loads are of great significance for the exploration and development of coalbed methane and the safe mining of coal. In this study, the in situ industrial μCT scanning experiments of gas-bearing coal under triaxial compression conditions was carried out using a loaded coal rock industrial μCT scanning system. The computed tomography (CT) scan images of different deformation stages were obtained. The temporal characteristics and spatial evolution patterns of fractures during gas-bearing coal rupture were investigated by combining image retrieval techniques and fractal theory. The results show that (1) as the axial load increases, the maximum similarity of the CT images showed a gradually decreasing trend. (2) Under the triaxial compression conditions, the number of two-dimensional cracks in a coal-containing gas at different spatial positions exhibited a changing pattern in which it slowly decreased before rapidly increasing. (3) The patterns of change in the three-dimensional fracture rate, fracture density, and fractal dimension were quite similar, showing four stages of slow decline, slow growth, sharp growth, and slow growth again. In contrast, the Euler number exhibited the exact opposite pattern of change. (4) The coal sample space showed prominent zonal failure characteristics. The bottom of the coal sample space position (Area C) near the loading indenter had the most developed cracks and serious damage, the middle of the coal sample space position (Area B) was the second, and the upper of the coal sample space position (Area A) near the fixed indenter had slow fracture development and minimal damage.

Calibration Method and Material Constants of an Anisotropic, Linearly Elastic and Perfectly Plastic Mohr–Coulomb Constitutive Model for Opalinus Clay

AbstractNagra, the cooperative for developing and implementing a long-term radioactive waste depository in Switzerland, identified Opalinus Clay as the most suitable host rock for deep geological containment. This paper deals with those features of Opalinus Clay that are important for the design and construction of the underground structures. Consolidated drained (CD) and consolidated undrained (CU) triaxial compression tests on specimens from deep boreholes revealed that Opalinus Clay exhibits pronounced stiffness and strength anisotropy, dependency of stiffness on the initial confining pressure, slightly non-linear pre-failure stress–strain behaviour, and a drop in axial resistance after a certain amount of shearing. Within the scope of establishing a rigorous—yet practical—design approach for the repository tunnels and caverns, the simplest possible constitutive model capable of reproducing the main aspects of the Opalinus Clay behaviour is adopted. The non-associated linear elastic and perfectly plastic MC model is chosen as a starting point, on account of its wide use in tunnel engineering practice, its simplicity, and the clear physical meaning of its parameters. This paper presents a systematic and robust calibration method for an extended version of this model, which considers the pronounced strength and stiffness anisotropy of Opalinus Clay. The paper additionally provides the full suite of the equations that describe the model behaviour under triaxial CU or CD testing conditions and for any bedding orientation relative to the specimen axis. The equations are employed to determine ranges of material constants for two varieties of Opalinus Clay, based upon the results of 73 CU and CD tests. A thorough comparison between the model predictions and the experimental response is conducted, to demonstrate the versatility and limitations of the constitutive model and of the proposed calibration approach.

Stress‐Induced Anisotropic Poroelasticity in Westerly Granite

AbstractWe measured poroelastic properties of cracked granite under triaxial conditions, at elevated confining pressure and a range of differential stresses. Skempton's coefficients and undrained Young's modulus and Poisson's ratio were determined directly by recording in situ fluid pressure during rapid cycles of axial and radial stress. Drained properties were measured both statically and dynamically at ultrasonic frequencies. At a given confining pressure, increasing differential stress leads to the development of elastically transverse isotropy, with symmetry axis aligned with the compression axis. Skempton's coefficients are also anisotropic, with larger changes in pore pressure in response to radial stress (coefficient Bx) than to axial stress steps (Bz). The anisotropy in the Skempton coefficients increases with increasing differential stress, with Bz decreasing and Bx slightly increasing. The evolution of static moduli and the Skempton coefficients is well approximated by Gassmann's equation using dry moduli obtained from ultrasonic measurements. Simplified predictions of the Skempton coefficients based on crack density tensors inverted from dynamic data also shows acceptable agreement with direct observations. Perfect quantitative agreement is not reached, due to the imprecision of our dynamic measurements, model simplifications, and inherent differences between static moduli obtained using stress steps of several MPa stress and dynamic ultrasonic stress oscillations.

Mechanical characteristics and energy evolution in a rock mass with a weak structural plane

The present aims to investigate the mechanical characteristics and energy evolution in rock masses containing weak structural planes under conventional triaxial loading conditions. Using a fluid–solid coupling test system of coal rock, numerous conventional triaxial compression tests were performed on rock masses at various dip angles of the structural plane. The obtained empirical outcomes revealed that the deviatoric stress–strain curve of the weak structural plane rock mass with an inclination angle greater than 20° rises step-by-step. On the macro level, slip-stability occurs on the upper and lower parts of the rock mass on the weak structural plane. Then mechanism of the slip-stability phenomenon is explored by analyzing the stress level in the rock mass with various inclination angles. It is found that the energy evolution during deformation and failure reflects the damaged state of the rock. Accordingly, the concept of ‘slip dissipation energy’ is proposed, and the values of each energy are calculated. The results have a good correspondence with the deviatoric stress–strain curve. Furthermore, it was found that the energy evolution of rock mass with a weak structural plane can be primarily classified into four stages, including storage of the initial energy, slip dissipation, abrupt increase in the pre-peak dissipation energy, and sudden drop in post-peak energy. Rock masses with various levels of dip angles exhibit similar elastic strain energy and dissipation energy at the peak point, demonstrating that energy evolution is dominated by energy storage and dissipation. At the same time, a negative correlation is observed between the structural plane dip angle and the occurrence of instantaneous impact instability failure in rock masses, indicating that a greater dip angle makes the rock mass less prone to experiencing instantaneous impact instability failure. This article provides a new idea for analyzing the geological disasters caused by external disturbances.

Investigation of the anisotropic mechanical response of layered shales

AbstractLayered shales exist widely and are often encountered during shale gas development. However, the mechanical response of layered shales is significantly affected by the existence of beddings, resulting in the obvious anisotropy characteristics regarding deformation, strength and failure mode. To clarify the underlying mechanisms of shale anisotropy that control the safety of engineering projects, the numerical simulation and theoretical analysis were conducted. The results show that with the growth of confining pressure, the compressive resistance of shales gradually increases, the shear fractures govern the instability and the anisotropy index decreases. Furthermore, several strength criteria for layered rock masses were summarized, and the modified Jaeger strength criterion was proposed by introducing the anisotropic parameter . It can effectively reflect the failure modes and strength features of layered shales under triaxial conditions with a higher accuracy. Besides, the variation of cohesion and internal friction angle of layered shale samples was comprehensively analysed under the triaxial conditions. Clearly, as the inclination angle of bedding planes increases, the cohesion of layered shales first decreases, but then increases under triaxial compression, showing the ‘U’‐shaped changing trend. Additionally, the internal friction angle of layered shales gradually increases with the increase in the inclination of bedding planes.

Generalized hydro-mechanically coupled hypoplastic constitutive model for unsaturated collapsible soils

In this paper, a generalized hypoplastic constitutive model for unsaturated soils based on the work of Fuentes and Triantafyllidis [2013] is presented. The constitutive model is formulated in terms of effective stresses, degree of saturation and suction. The main feature of the model is a Limiting Surface (LS) which describes the maximum achievable void ratio as a function of mean effective stress and degree of saturation. The LS allows to capture the wetting-induced collapse of initially unsaturated soils. The performance of the proposed model is demonstrated by backcalculation of a well-documented experimental study on over 30 samples of compacted Pearl clay by Sun et al. [2004] under isotropic as well as triaxial loading conditions. For this purpose, the proposed model is coupled with a hypoplastic model for the soil-water retention curve, which interrelates the effective degree of saturation with the suction and the void ratio.

Experimental Study of Compact Sandstone Deformation Under Axisymmetric Triaxial Loading Along Specific Paths in Stress Space

The deformation of rocks well below their ultimate strengths is frequently described through the constant stiffness moduli of the linear elasticity theory. In addition, the isotropic material approximation is usually used as the basic approach. Particularly in sedimentary rocks, local inhomogeneities, anisotropy, and irreversible processes, mainly related to the gradual breakage of grain joints, can affect their deformation behavior from the beginning of the loading. Consequently, the stiffness moduli measured under triaxial conditions are effective parameters, which may depend on the loading path in the stress space. Therefore, a complex experimental study of the deformation response of compact sedimentary rock (Brenna sandstone) along various paths in triaxial stress space was prepared to understand this dependence. In addition, a detailed analysis of the rock composition and structure of this compact sandstone was carried out. This paper presents an initial experimental study that is based on a loading method using alternative stress paths that correspond to different modes of the monotonic increase in differential stress from an initial isotropic compression state. In the experiment, the dependence of stiffness moduli on the loading path was found. Differences in rock deformation for conventional triaxial compression and extension can be attributed to a slight rock anisotropy originating from the stratification. The different behavior of deformation and related stiffness moduli along so-called reduced triaxial paths and conventional paths indicates that irreversible processes must be taken into account.