Mechanical Behavior Of Rock Research Articles

Experimental and numerical study on the interaction between holes and fissures in rock-like materials under uniaxial compression

Holes and fissures, regarded as typical defects, dominate a critical role in the mechanical behavior of rock. To investigate the effect of different horizontal distances L or L′ between the centroids of holes and fissures on the mechanical properties of pre-flawed rock-like material, two types of rock-like material specimens with holes and fissures are fabricated and subjected to uniaxial compression using Digital image correlation (DIC), Acoustic emission (AE) monitoring, Computerized tomography (CT) scanning, and two-dimensional Particle flow code (PFC2D). These results demonstrate that the peak strength, peak strain and elastic modulus all show a monotonically nonlinear decrease with increasing L or L′. Based on the DIC and CT methods, three rock bridge coalescence modes can be distinguished: tensile-tensile, shear-shear and tensile-shear modes. Moreover, the damage of the rock-like specimens, in the entire loading process, exhibits notable progressive failure characteristics in the strain localization zones. The crack initiation and coalescence cause the deformation curve to undergo a stress drop with a surge in the AE events and in the accumulated AE counts from AE monitoring. There is good agreement between the numerical simulation results and the experimental testing results, which further heighten the instability mechanism of defective rock engineering structures.

Damage evolution analysis of rock under Uniaxial compression and Brazilian splitting based on discrete element method

In order to better analyze the mechanical behavior of rock in uniaxial compression and Brazilian splitting, numerical model was established according to laboratory test by PFC2D particle flow program, and the simulation results were compared with the experimental results. The results show that when the rock reaches the peak stress, the failure curve of cement appears an obvious turning point, and the failure rate of cement increases.The compressive strength of rock is much greater than the tensile strength under compression condition. The preloading method is more detailed for experimental restoration, and it provides certain reference significance for rock simulation in the future.

Modeling discrete fractures in continuum analysis and insights for fracture propagation and mechanical behavior of fractured rock

Abstract This paper presents a procedure for modeling discrete fracture initiation, deformation, and propagation in continuum analysis of rock, and provides numerical simulations to evaluate performance of the procedure against analytical solutions and laboratory data. The procedure is based on aggregating the mechanical behavior of evolving discrete fractures and unfractured rock and provides specific information about fracturing; such as when and where fractures may occur and the type (tensile or shear), geometrical attributes, and aperture of each fracture. By storing fracture geometry as continuum properties that are used internally to generate geometrical parameters needed for analysis, the procedure models the geometry and mechanical behavior of discrete fractures explicitly in continuum analysis without including the fractures in the model grid. Numerical simulations are described for typical laboratory loading conditions such as triaxial compression and extension, and Brazilian testing. The results are compared with laboratory data, analytical solutions, and established concepts to make a case that the procedure performs satisfactorily and can be relied upon for understanding and predicting rock mechanical behavior. Furthermore, the paper discusses insights based on the simulation results for understanding rock fracturing; mechanical behavior of fractured rock; and large-scale behavior such as localization of rock deformation, stress control of fracture mechanisms in failure zones, and conditions for occurrence of multiple parallel fractures.

Complex deformation of naturally fractured rocks

Strain is a key parameter in the evaluation of rock mechanical properties and failure behavior. Strain is usually measured using strain gauges, however, this laboratory method has inherent uncertainty in the attachment of sensitive gauges to the rock surface and it is limited to one-point strain measurement. In complex geometries such as rock samples with natural fractures or lamination, that classical approach cannot provide the whole picture of strain development in such complex geometries. To overcome these challenges, the application of optical technique with image processing is proposed. The optical technique has the advantage of being a non-contact method and it provides quantitative visualization of full-field strain measurement.To examine quantitative visualization of strain development, DIC technique was first conducted on a homogeneous sandstone sample as a benchmark. The results verify that the maximum tensile strain is developed at the central vertical line of the sample as it was expected from theoretical solutions. This DIC measurement matches the post-failure fracture pattern of the specimen. Then the technique was applied on the Buda Limestone samples with horizontal, sub-horizontal or multiple complex natural fractures (sealed or partially open) and inclusions while the samples were under diametrical compression experiment. The results of this study provide further insight into the role of natural fractures on induced fracture initiation and propagation under this specific testing condition. Horizontal natural fractures are planes of maximum compressive strain which can delay the propagation of vertical tensile fractures. The maximum amount of tensile strain usually initiates at the boundary of these natural fractures and vertical tensile fractures usually deviate toward horizontal fracture for a short distance before turning back to propagate vertically following the maximum stress path. Full-field surface deformations are mapped optically in the crack–inclusion vicinity where DIC results showed that crack front is arrested by the inclusion for the complete fracture event. In contrast to the failure pattern in homogenous sandstone specimen, complex fracture pattern was observed on several specimens with multiple fracture network. Fracture slippages along the natural fracture, fracture deviation was observed in samples with steep inclined natural fractures.The results of this study can help us to better understand the complex failure mechanism in naturally fractured media and elaborate on various mechanisms of failure under diametrical compression tests. DIC is a powerful technique in providing the dynamic strain development over the surface of the sample in real-time, thus it can provide the fracture initiation and propagation in such heterogeneous rock media.

Influence of Super-Critical CO2 on the Strength and Fracture Behavior of Brine-Saturated Sandstone Specimens

The mechanical behavior of rock is one of the most important parameters to evaluate the potential for geological carbon dioxide (CO2) sequestration (GCS); therefore, the study of rock strength evolution and fracture behavior after CO2 injection is helpful in the long-term stability and safety of GCS engineering. In this study, uniaxial compression, Brazilian splitting and fracture tests were carried out on sandstone specimens with brine saturation or brine-super critical CO2 (scCO2) co-saturation. The influences of brine salinity and scCO2 injection on the uniaxial compressive strength (UCS), Brazilian tensile strength (BTS) and fracture toughness of sandstone were investigated. The experimental results showed that the UCS, BTS and fracture toughness of brine-saturated sandstone increased with increasing NaCl concentration but decreased after scCO2 injection. Furthermore, increments in the elastic modulus and average stiffness of brine-scCO2 co-saturated sandstone were observed relative to those under brine saturation. To investigate the change of mineral composition and micro structure during brine immersion and scCO2 injection, X-ray diffraction analysis, scanning electron microscopic observation and mercury intrusion porosimetry test were performed. Composition changes and dissolution of quartz were not observed, but many micro pores were created after scCO2 injection, thus increasing the porosity and reducing strength and fracture toughness. Finally, the mechanism of brine-scCO2 saturation in altering mechanical properties was discussed. These experimental results are expected to increase the understanding of the mechanical response of rock after scCO2 injection in deep saline aquifers.

The Role of Load Control Modes in Determination of Mechanical Properties of Granite

Circumferential strain-control tests were suggested to obtain the complete stress–strain curves (SSCs) of intact rock. However, compression test performed by the axial strain-control loading is mostly used to obtain the strength parameters and the SSCs. The influences of load control modes on the mechanical behavior of rock have not been fully investigated and understood. In this study, triaxial compression tests are conducted on granite specimens loaded by using both axial strain-control and circumferential strain-control modes to examine influences of load control modes on the determined mechanical properties. The occurrence mechanism and influencing factors of class II behavior are studied, and the potential application of the class II SSC in the evaluation of brittle failure of hard rock is also discussed. Results show that the peak strength, elastic modulus and fracture angle are generally higher in the axial strain-control test than in the circumferential strain-control test, and the failure in the former is also more violent than the latter under the same confining pressure. The much lower and constant circumferential deformation rate applied in the circumferential strain-control test is the dominant factor that favors the recovery of the complete post-peak SSC. The lower measured values of strength and elastic modulus are also associated with the lower deformation rate in the circumferential strain-control test, with a higher degree of damage and cohesion weakening occurring inside the rock. The development of the class II SSC is attributed to the axial strain recovery during the release of the stored elastic energy, which is influenced by the ratio of elastic energy to dissipated energy in the pre-peak stage, and is also associated with the consumed energy with respect to plastic deformation or initiation and propagation of new cracks in the post-peak stage. The class II SSC can aid the differentiation of the energy accumulation and consumption of different brittle rocks, which are usually characterized by a more abrupt and larger stress drop in the axial strain-control test. It can then be used to evaluate the strain rockburst potential of a particular rock type.

Numerical study of the circular opening effect on mechanical behaviour of rock under confinement

Opening holes in rock including their size and distribution can affect the performance of rock-related structures. A good understanding on this will contribute to, for example, rock cavern design, and construction, tunnelling, and mining engineering. To improve the understanding, a comprehensive investigation of the opening hole effect on the rock mechanical behaviour under biaxial loading condition is carried out by virtue of a hybrid continuum-discrete element method. Laboratory specimens with both single hole and multi-hole of various radii are investigated and compared with the cases subjected to uniaxial compression. It is demonstrated that the confining pressure can increase both the stiffness and strength due to delaying the crack initiation and propagation. The increase due to the confining pressure is more evident for the compressive strength. For single hole specimens with 0.75 mm radius hole, the increase ratio of the compressive strength is a linear increasing function with width and the increase ratio ranges from 2.15 for the specimen with 3.5 mm width to 2.45 for 10 mm width. For the single hole specimen with 10 mm width, the increase ratio starts at 2.13 for the specimen with 0.75 mm radius hole, ascending to the peak of 2.37 for the specimen with 1 mm radius hole, followed by a decline to 2.2 for the specimen with 1.25 mm radius hole. However, for the multi-hole specimens, the increase ratio varies from 1.66 to 3.13. In addition, to verify the influence of confining pressure magnitude on the performance of the rock specimens, totalling 10 confining pressure levels are applied and modelled. The simulation results show that even though there are opening holes in the specimens, the simulated compressive strength generally follows the generalised Hoek-Brown model.

Numerical Investigation of Mineral Grain Shape Effects on Strength and Fracture Behaviors of Rock Material

Rock is an aggregate of mineral grains, and the grain shape has an obvious influence on rock mechanical behaviors. Current research on grain shape mostly focuses on loose granular materials and lacks standardized quantitative methods. Based on the CLUMP method in the two-dimensional particle flow code (PFC2D), three different grain groups were generated: strip, triangle, and square. Flatness and roughness were adopted to describe the overall contour and the surface morphology of the mineral grains, respectively. Simulated results showed that the grain shape significantly affected rock porosity and further influenced the peak strength and elastic modulus. The peak strength and elastic modulus of the model with strip-shaped grains were the highest, followed by the models with triangular and square grains. The effects of flatness and roughness on rock peak strength were the opposite, and the peak strength had a significant, positive correlation with cohesion. Tensile cracking was dominant among the generated microcracks, and the percentage of tensile cracking was maximal in the model with square grains. At the postpeak stage, the interlocking between grains was enhanced along with the increased surface roughness, which led to a slower stress drop.

Transversely Anisotropic Damage Characteristics of Loaded Rock under Freeze-thaw Cycles

Flake metamorphic rocks and sedimentary rocks tend to show obvious transversely isotropic mechanical properties in deformation and strength because of the existence of weak structural surface or soft-hard interlayer structure. The rock in cold area is affected by load and freeze-thaw cycles, and the prevention and control of freeze-thaw disaster has become an urgent problem to be solved in the construction of cold area. Based on the strength of Rock Micro Element subjecting to Weibull random distribution and the macroscopic statistical damage model of rock, this paper used the transversely isotropic elastomer model to describe the damage evolution equation of freeze-thaw rocks in the whole process of the load deformation, and established the corresponding damage constitutive model. The results showed that this model more accurately describes the effect of freeze-thaw cycles on rock mechanical behavior, and had positive theoretical and practical significance for solving engineering problems in complex rock body.

A Study of Uniaxial Compressive Strength of Shale Based on Homogenization Method

Uniaxial compressive strength of shale is one of primary input parameters during shale gas development. In order to analyze uniaxial compression failure mechanism and obtain strength formula, the present study regards shale as heterogeneous material composed of pores, brittle minerals and clays. Pores are distributed as oblate ellipsoidal inclusion in clays, while brittle minerals are distributed as spheroidal inclusion in the equivalent clay matrix formed by pores and clays. With the help of the basic solution to Eshelby’s matrix–inclusion problem and the homogenization method, a two-step homogenization framework for shale was established. The influences of pore fluid on the rock mechanical behavior were also discussed by categories. Based on the composite mechanics, the failure strength of shale under uniaxial compression was deduced at last. The results show that the shale strength is affected by the mechanical properties of diagenetic minerals and enhanced with the increase of brittle mineral content. Since pore water promotes the initiation and propagation of cracks, shale strength decreases non-linearly with increasing water saturation.

Stress and strain evolution during single-layer folding under pure and simple shear

Folds in rocks are commonly used in geology for strain analysis. They contain information about rock rheology, and the kinematics and mechanics of deformation. The systematic analysis of the evolution of stress and strain during rock folding can provide key information on the mechanical behaviour of rocks and the efficiency of the folding process. In order to investigate the evolution of rock rheology during fold development, a series of two-dimensional simulations of single-layer folding are presented here. They are run using the finite element method BASIL, integrated within the software platform ELLE, to simulate linear and non-linear viscous deformation. The kinematics of deformation, the competence ratio between the folding layer and surrounding matrix as well as the stress exponent of the power-law viscous material are systematically varied. The results allow comparing the stages of folding under different deformation kinematic conditions. For all simulations the folding amplification process starts when the second invariant of the strain rate tensor in the competent layer deviates from the theoretical strain rate curve for a homogeneous material, which corresponds to a viscosity ratio between layer and matrix of m = 1. The relative time when the fold amplification starts is determined by the viscosity ratio between the competent layer and its surrounding matrix, the initial layer orientation with respect to the shear plane, the kinematics of deformation and the stress exponent. The folding process is more effective in cases with high viscosity ratio, non-linear rheology and layers initially oriented at a low angle with respect to the shear plane, because the second invariant of the strain rate tensor at the layer deviates earlier from the theoretical curve. The results also show differences depending on the boundary conditions, where (1) folding a competent layer requires less work in simple shear than in pure shear, and (2) the geometrical softening experienced by the competent layer due to fold development is followed by a hardening stage in pure shear and by a major softening phase in simple shear. The simulation results suggest that the decrease of stress of a competent layer without decreasing the mechanical strength has a direct influence on the behaviour of a lithospheric layer around the crust-mantle boundary, which may experience geometrical softening depending on the tectonic settings rather than material softening due metamorphic reactions or grain size reduction.

A Case Study on the Asymmetric Deformation Characteristics and Mechanical Behavior of Deep-Buried Tunnel in Phyllite

When tunneling through deep-buried layered soft strata, asymmetric deformation of surrounding rock and asymmetric mechanical behavior of supporting structures are often encountered. This paper investigates the anisotropic mechanical properties of deep-buried carbonaceous phyllite and its influence on the asymmetrical mechanical behavior of supporting structures in the Zhegu mountain tunnel in Sichuan Province, China. It is a typical road tunnel that suffered from large asymmetrical deformation and cracking of the secondary lining due to layered strata and high geo-stresses. Firstly, experimental tests were conducted to investigate the influence of bedding angle on the mechanical properties and failure behavior of phyllite. Then, the UDEC numerical software was adopted to study the effects of the lateral pressure coefficient, rock layer inclination angle, bedding spacing and shear stress on the mechanical behavior of supporting structures. Moreover, a field test was conducted to measure the pressure between the surrounding rock and the primary support as well as the internal force of the steel arch and the secondary lining. Based on the field data and numerical simulation results, it can be concluded that the asymmetrical deformations of surrounding rock and the cracking of secondary lining in the Zhegu mountain tunnel were results of the coupling effect of layered soft rock and shearing action along the foliation.

Quartz types and origins in the paleozoic Wufeng-Longmaxi Formations, Eastern Sichuan Basin, China: Implications for porosity preservation in shale reservoirs

Abstract Quartz in shales has been demonstrated to exert a significant effect on shale gas production by influencing rock mechanical behavior and reservoir porosity; however, quartz types and origins in shales are complicated and challenging to study due to their fine-grained nature. In this study, we propose combining thin section images, scanning electron microscopy (SEM) images, energy dispersive spectroscopy (EDS) maps, cathodoluminescence (CL) images and geochemical data to investigate quartz types and origins in shale formations. Shale samples from the Ordovician Wufeng-Silurian Longmaxi Formations, Eastern Sichuan Basin, China were used to study quartz types, origins and the effect of quartz cementation on porosity development. Samples from the Wufeng-Longmaxi Formations have TOC contents in the range of 0.5–4.7 wt%, averaging 2.7 wt%, and are currently in the thermally overmature stage. Five types of quartz, including silt-size detrital quartz, siliceous skeletal fragments, quartz overgrowth, clay matrix-dispersed microquartz, and aggregates of euhedral quartz, were identified. The ternary diagram of Fe–Al–Mn, the cross-plot of SiO2 versus Zr, and the cross-plot of Si versus Al suggest that the dissolution and reprecipitation of siliceous skeletons may provide the major source of silica for quartz cementation in the lower part of the Wufeng-Longmaxi Formations, and released silica as a result of smectite to illite transformation is also important for authigenic quartz formation in the upper part of the Wufeng-Longmaxi Formations. Our SEM images suggest that the rigid framework formed by quartz cementation not only prevents primary interparticle pores from compaction but also favors the generation of organic matter-associated pores.

Calibration of micro-scaled mechanical parameters of granite based on a bonded-particle model with 2D particle flow code

From a microscopic perspective, the mechanical behavior of rocks can be well simulated by particle discrete element method. However, the ideal mechanical properties under macroscopic compression and tension conditions of the granular system require not only reasonable micro-parameters but also consider the mineral distribution in rock microstructure. In this study, the internal microstructure of granite was characterized based on digital images. The cellular automata method was used to construct a discrete element model of clustered particles, and a rapid and effective calibration method for rock microscopic parameters was established. Numerical results significantly relate with laboratory test results, and the microscopic mechanical parameters of the rock were rapidly predicted. Clustered discrete element model simulated the macroscopic mechanical behavior of the investigated rock by considering microscopic rock structure while ignoring particle shape. Results showed that bond strength ratio of the filler–matrix in the numerical sample can significantly affect the compressive–tensile strength ratio. Further, the internal mineral proportion and degree of mineral contact damage strongly influenced the macroscopic mechanical behavior of the investigated rock. Results of this study can provide basis for the construction of micro-scaled model and calibration of microscopic parameters for investigation of rock mechanical behavior.

Numerical investigation on heat extraction performance of a multilateral-well enhanced geothermal system with a discrete fracture network

Our previous study (Song et al., 2018) proposed a novel enhanced geothermal system (EGS) with multilateral wells and demonstrated that it had greater heat extraction performance than double-well EGS. However, to further enhance the heat extraction performance of multilateral-well EGS, an efficient and complex fracture network needs to be created to connect injection and production wells. In order to know which kind of discrete fracture network (DFN) should be created to improve the heat extraction performance of multilateral-well EGS, it is extremely important to investigate effects of DFN on multilateral-well EGS performance. Therefore, in this study, we develop a thermal-hydraulic-mechanical (THM) coupling model to investigate the heat extraction performances of various DFNs. The model is verified by an analytical solution. Based on the model, effects of rock mechanical behavior on fracture permeability evolution and EGS heat extraction performance are studied. The sensitivity analysis of reservoir properties and injection temperature on THM coupling process are conducted. Influences of fracture parameters, including number of fractures, fracture length and orientation, on multilateral-well EGS performance are investigated. The results indicate that the rock contraction could increase fracture permeability and promote the preferential flow and thermal breakthrough. The injection temperature and reservoir properties have significant effects on the rock deformation and heat extraction performance of multilateral-well EGS. The DFN with complex and longer fractures and without too many direct connections between lateral wells and fractures is beneficial for multilateral-well EGS performance. The results of this study provide significant suggestions for the fracturing operation of multilateral-well EGS.

Mechanical stability of granite as thermal energy storage material: An experimental investigation

Thermal energy storage integrated with solar power plants can be considered as a promising way in improving the efficiency and overcoming the intermittency of solar power plants at low costs. It is proposed that natural rock is good and suitable for thermal energy storage material in concentrating solar power plants at high temperature of approximately 500–700 °C. However, more attention has been devoted to thermal capacity and conductivity when selecting the potential rock, while little work has been done in the field of rock mechanical behaviors in this particular situation where rock need to keep stable after undergoing cyclic high temperature. This paper aims to evaluate the potential of granite to be thermal energy storage material in mechanical aspect, by analyzing the mechanical characteristics of granite after exposed to high-temperature treatment with temperature cyclically changing between 20 °C and 650 °C. Uniaxial compression tests were carried out to reveal the effect of thermal cycles on the crack damage development, strength decrease and failure mode of granite. The results showed that, micro cracks would generate in granite after exposed to high temperature and consequently lead to the deterioration of rock mechanical characteristics, especially in the first thermal cycle when there were dramatically drops in the peak strength and elastic modulus of granite. The deterioration reached almost constant when granite was thermally cycled more than 20 times. The changes of mechanical behaviors were explained through the microstructure measured by SEM. Thermal cycle effects on the failure mode of granites were investigated by monitoring acoustic emissions and analyzing fracture surface during uniaxial compression test. The brittle-ductile transition of granite was enhanced with the increase of thermal cycle.

A comprehensive parametric study of grain-based models for rock failure process simulation

Grain and contact are the two key components in 3DEC-GBMs (grain-based models) because they control the micro-mechanical behavior and consequently the macro-mechanical behavior of rock. Three types of grains – rigid, elastic, and breakable grains – are considered in this study to explore the influence of grain properties on the mechanical behavior of rock. Equivalent 2D plane strain problems are solved using 3DEC to reduce computation time. A non-uniform distribution of grain size is used to generate numerical models using Neper, a software package for polycrystal generation and meshing. A comprehensive parametric study of properties of contact and grain of the three types of grains is conducted and calibration procedures are suggested for numerical modeling. The modeling results indicate that both the contact and the grain properties affect the macroscopic mechanical behavior of synthetic rock specimens. All the three types of grains produce reasonable results for pre-peak deformation (E and υ) and macroscopic strength (UCS, σt, C and ϕ) parameters. Each grain type has advantages and disadvantages in numerical modeling. Rigid grains cannot produce volumetric strain properly and a near-zero residual friction angle of contact is needed to capture post-peak deformation behavior due to the grain interlocking effect. Elastic grains also need a very low residual friction angle of contact and brittle rock deformation behavior cannot be captured. The complex calibration procedure and long computation time are the main issues of breakable grains, although it simulates well the volumetric strain, does not require a very low contact residual friction angle, and captures brittle rock behaviors better than other two types of grains. The findings from this study are useful for rock failure process simulation using the 3DEC-GBM modeling approach.

Mechanical and acoustic behaviors of brine-saturated sandstone at elevated temperature

The mechanical behavior of rock is essential to estimate the capacity and long-term stability of CO2 storage in deep saline aquifers. As the depth of reservoir increases, the pressure and temperature that applied on the rock increase. To answer the question of how the confining pressure and temperature influence the mechanical behavior of reservoir rock, triaxial compression experiments were carried out on brine-saturated sandstone at elevated temperature. The triaxial compressive strength of brine-saturated sandstone was observed to decrease with increasing testing temperature, and the temperature weakening effect in strength enhanced with the increase of confining pressure. Sandstone specimens showed single fracture failures under triaxial compression. Three typical regions around the main fracture were identified: fracture band, damaged zone and undamaged zone. A function was proposed to describe the evolution of acoustic emission count under loading. Finally, the mechanism of elevated temperature causing the reduction of strength of brine-saturated sandstone was discussed.

Influence of the variable stoping speed on the occurrence mechanism of rock burst

Many field investigations have proven that the stoping speed of mining face is closely related to the amount of energy released from hard roof fracturing. Taking the Dongtan Coal Mine as the engineering background, we first analyze the relationship between the stoping speed and the microseismic activity. Then, the effect of the variable loading rate on the mechanical behavior of rock or coal is studied using PFC2D simulation. Finally, the occurrence mechanism of rock burst induced by the stoping speed variation under the hard roof condition is revealed. The stoping speed variation is not advantageous for the slow release of elastic energy stored in the roof and coal seam, and it can easily induce high energy events, which can reach 2.88–6.81 × 106 J. Under a variable loading rate condition, the energy storage capacity of coal and the released kinetic energy increase. When the stoping speed increases, the energy stored in the coal seam simultaneously increases, which implies that the dynamic balanced system is disturbed, and a rock burst may occur. When the stoping speed decreases, the new dynamic balanced system cannot absorb the entire pre-stored energy, and some of that energy will be released, which may also induce a rock burst.

The influence of hydrothermal brine on the short-term strength and elastic modulus of sandstones from exploration well EPS-1 at Soultz-sous-For\xeats (France)

Laboratory studies designed to provide the strength of rocks are typically performed on either dry- or water-saturated rock samples. To better understand the mechanical behaviour of rocks in a geothermal context, we provide here the short-term strength and static elastic modulus of sandstones from exploration well EPS-1 at the Soultz-sous-Forêts geothermal site (France) saturated in hydrothermal brine sourced from the adjacent production well GPK-2. We performed 59 uniaxial compressive strength experiments on samples of Buntsandstein sandstones sampled from six depths (1008, 1022, 1069, 1107, 1290, and 1414 m). Samples were deformed oven-dry (i.e., unsaturated), water-saturated (deionised water), or brine-saturated. Relative to the dry state, strength was reduced by between 24 and 39% and elastic modulus was reduced by between 9 and 19% when the samples were saturated with water. However, we observed no measurable difference in strength and elastic modulus between samples saturated in water and brine. These reductions in strength and elastic modulus in the presence of water or brine are considered the result of a reduction in specific surface-free energy. Changes to short-term strength and elastic modulus in the presence of hydrothermal brines likely require brines with higher salinities and/or lower values of pH than those typically found within the Upper Rhine Graben (the brine from GPK-2 has a salinity of ~ 10% and a pH of 5.5). These new data can be used to assist reservoir prospection, stimulation, and optimisation strategies at the geothermal sites within the Upper Rhine Graben.