Existing methods for compression tests have enabled the observation of class-II post-peak or snap-back behaviour. However, capturing tensile behaviour in rock testing is still challenging due to stronger snap-back in tension. This work adopts the recently developed Advanced Universal Snap-Back Indirect Tensile test (AUSBIT) to obtain the complete tensile load-displacement behaviour of granite and sandstone Brazilian discs in the post-peak stage through controlled lateral displacement. Digital Image Correlation (DIC) and Acoustic Emission (AE) were employed to analyse the progressive failure mechanisms when compared with the conventional Brazilian tests. Results show that AUSBIT enables controlled failure at extensive lateral displacements by allowing the stable propagation of microcracks. AE data further reveal that cracks formed in AUSBIT release significantly less energy compared to conventional tests. These phenomena were more significant in granite, showing the effectiveness of AUSBIT for controlling the tensile failure of brittle class-II rocks and in attaining the post-peak behaviour.

We have investigated the mode I fracture toughness (K_IC) of granite samples in the presence of various fluids pseudo-compact tension (pCT) test. Prior to the fracture toughness tests, several granite specimens were immersed in deionized water (DIW), hydrochloric acid (2.7M HCl), and sodium hydroxide (0.2M NaOH) solutions for 8 days to evaluate the effects of different reactive environments on K_IC. In addition, a group of specimens of the same rock were submitted to a 24-day immersion cycle using the same fluids (starting with the caustic NaOH solution, then by acidic HCl and finally with DIW), which consecutively soaked the samples every 8 days. The experimental results have been analyzed to assess the corresponding dissipation energies and to identify chemo-mechanical couplings eventually involved in crack initiation and propagation. Results show that, when compared with dry samples, those soaked in any fluid are weakened with a reduction in the threshold energy for crack initiation. However, the different fluids do not result an identical impact over K_IC. We observe that lowest affection is induced by the acidic solution, followed by the caustic one, and finally by DIW (K_IC,dry > K_IC,HCl > K_IC,NaOH > K_IC,DIW). Thus, deionized water exhibits the greatest reduction in fracture toughness (up to 30 %) and the specimens also have a lower average stiffness than the other immersion methods. According to available research (experiments performed with glass materials and molecular dynamics simulations), this may be attributed to micro-scale (molecular scale) processes by which the smaller kinetic diameter of water molecules makes them more accessible to the crack tip, facilitating the hydrolysis of siloxane bonds. Interestingly, despite the fact that the specimens were eventually immersed in DIW in the cyclic test, the K_IC obtained in this case is still higher than that resulting from the individual exposure to the single DIW fluids (K_IC,cycle > K_IC,DIW). That results from the residual hydrolyzing species (Na⁺/H₃O⁺/OH^-, etc.) at the crack tip of the specimens during the cyclic test. The assessments of bulk mechanical energies reveal that, regardless of the chemical environment, approximately 40% of the energy delivered to the samples in each test is consumed by crack initiation, while about 60% is consumed by crack propagation. These results highlight that the chemical environment at the crack tip is the primary factor influencing the subcritical fracture behavior and provide important insights for accurately assessing the fracture toughness of rocks in the presence of fluids.

Direct tensile testing is generally accepted as the most accurate method of determining tensile strength, but indirect methods are commonly employed due to the difficulty and precision re-quired to obtain viable results with the direct method. Accurate values of tensile strength are important, especially regarding design. Thus, values obtained from the direct tensile test are beneficial to be able to utilize and compare them to other experimental values and different methods. This paper presents the development and implementation of the direct tensile test at the Geotechnical Engineering Laboratory of the University of Cantabria, following the ASTM standards. The lessons learned are highlighted. The results of direct tensile tests on Moleanos limestone are here compared with the results of previous indirect tensile tests, namely the Brazilian (splitting tensile) test. The fracture pattern of the direct tensile tests is also presented and analyzed.

The ring test, which is one adaptation of the Brazilian test, was proposed in the 1940s. The laboratory test consists of the application of a diametric load on a ring specimen, in order to estimate the tensile strength indirectly. Its great advantage over the traditional test (disk samples) is that by having a point of weakness (the hole), it is guaranteed that the failure begins in the center of the specimen, a necessary condition for the Brazilian test to be valid. However, the ring test could not be used until the new empirical solution is proposed, because the result of the analytical solution is quite distant from the expected. The analytical equation is based on the theory of elasticity and does not consider the non-linearity of the rocks. According to this analytical solution, in the case of a specimen with a tiny hole, its tensile strength would be six times greater than that obtained with the Brazilian test. The empirical solution is independent of the rock type and correlates the load necessary to break a disc with the load that should be applied in a ring, is based on more than a hundred tests carried out on different materials and laboratories. In the present paper, the empirical solution is analyzed and the advantages/disadvantages of the different internal hole sizes are commented on. Also, how to prepare the ring sample is explained. Being highlighted that the sample preparation is very simple and does not need any special device. In the laboratory, sandstone blocks (lithic arkose) from Burgos (Spain) have been tested with different sizes of rings. The proposed empirical solution takes into account a change in the failure mechanism observed at certain hole sizes.

This review is focused on an innovative and non-destructive laboratory approach, referred to as IRTest, to estimate the rock porosity by Infrared Thermography. Based on the positive out-comes achieved through the use of Infrared Thermography for rock mass characterization, the study of the cooling behavior of rocks has suggested that the porosity grade is linked to the cooling speed of a previously heated rock specimen. The technique has been applied to different rock types, in terms of both porosity grade and lithology. Achieved results demon-strate that there is a positive linear relationship between rock porosity and CRI10 (Cooling Rate Index), corresponding to the infrared thermal monitoring of the rock cooling within a 10 minutes time window. IRTest was applied to differently shaped and sized rock samples, prov-ing the suitability of this technique on a variable statistical population, and suggesting the in-novative potential of Infrared Thermography for the rock laboratory characterization.

Rock mass shows bi-modularity behavior, consisting that elastic modulus having different ratios in compression and tension. Being the compressive elastic modulus always greater than the tensile modulus. In practice, the most common is to estimate the elastic modulus in compression, given that the uniaxial compression test is widely carried out. The direct tensile test requires a specific device, so the tensile strength usually is estimated by the indirect tensile test (Brazilian test). Ye et al. (2009) proposed an equation to estimate the tensile elastic modulus with the Brazilian test, using strain gauges attached in the horizontal direction on both sides of the specimen. However, they did not have how to perform the direct tensile test to compare the results. In the present paper, the elastic modulus is obtained in three different ways: in the compression test, in the direct tensile test, and in the Brazilian test (diametric load). A series of laboratory tests has been done in anisotropic sandstone (lithic arkose), from Burgos, Spain. Being remarkable that the mechanical behavior of the anisotropic rock mass is dependent on the inclination of the foliation planes, the tests were carried out with inclinations of 0°(horizontal) and 90° (vertical). These two configuration are the extremes of tensile strength.

The measurement of mode I fracture toughness (K_IC) , which represents the resistance to the propagation of pre-existing defects under tensile stress, is crucial for various engineering applications involving rocks, such as tunnel boring, rock drilling, hydraulic fracturing, and oil exploration. Recently, the pseudo-compact tension (pCT) test has been proposed as a reliable method to measure K_IC in rocks under pure tension conditions, yielding consistent results for both fragile and ductile rocks. Although the pCT method offers several advantages, such as simple sample preparation, small sample requirement, and controlled fracture propagation beyond the peak load, its original approach requirements the use of a specially designed, large-size testing device. This limitation may restrict the broader adoption of this testing methodology. To overcome this drawback, we present in this work a simplified pCT test apparatus that can be easily installed in any conventional compression frame. The proposed device, thanks to its mechanical configuration, allows for application of true tension to the notch of the sample while the axial actuator of the frame operates in compression over the loading piston. The mechanical behavior of the prototype was assessed numerically with a finite element method model in ABAQUS, and experimentally using aluminum specimens. Additionally, to further evaluate its stiffness and performance, digital image correlation (DIC) was employed to obtain full-field strain characteristics of the critical, most stressed parts of the apparatus. To validate the new configuration, polymethyl methacrylate (PMMA) specimens with different notch lengths were tested. The results demonstrate that the new simplified pCT test system exhibits sufficient stiffness and provides comparable K_IC values with those previously obtained with the reference pCT testing device.

Shear stiffness is an important parameter governing deformation behavior and stress dis-tribution. However, its current use is inadequate for detailed models, particularly in sedi-mentary rocks. Most published shear stiffness data for sedimentary rocks are for joints at low normal stresses, with limited available at normal stresses above 1 MPa. This paper ad-dresses this deficiency by presenting results from direct shear testing for bedding parallel fractures under high normal stress and implementing a recently proposed method to isolate fracture deformations, this method is then validated using several measurement methods. The shear stiffness of 18 samples from the Bowen Basin (QLD, Australia) was obtained for different values of applied normal stresses (1 to 8 MPa). The results show a strong positive correlation between applied normal stress and shear stiffness. The findings high-light opportunities for improvement in current guidelines and emphasize the need for them to better reflect results and data processing protocols.

Solving engineering tasks and assessing the suitability of rocks as building raw materials requires determining the physical properties. Ultrasonic testing as nondestructive testing is useful for the initial assessment of elastic properties. Adapting seismic tomography technique for application at the laboratory scale using ultrasonic frequency waves allowed the characterisation of variations in ultrasonic propagation velocity inside the study granite specimen. The P- and S-wave velocities were measured using 54kHz and 250kHz transducers. The dynamic modules and anisotropy ratio were calculated based on obtained seismic wave velocities. The ultrasonic tomography method allowed for an initial assessment of the homogeneity of the rock medium, which allows an optimal selection of its lithological variety for a given engineering purpose.

Although the determination of joint shear strength of layered heterogeneous rock masses constitutes a challenge in engineering, since they are widely present in natural rock masses, the available scientific-technical publications are relatively scarce. Studies have mainly been focused on homogeneous rocks. Thus, the objective of this research is to evaluate the effect of heterogeneity on the shear behaviour of different types of rock joints and provide the basis for evaluating the stability of the heterogeneous rock masses, as well as to know the differences and similarities with respect to the behaviour of homogeneous rock joints. In this research, various direct shear tests have been conducted on artificial joints of heterogeneous rocks with different joint roughness coefficients, as well as tests on artificial joints of homogeneous rock in order to allow comparisons between them. The experiment consisted of performing 18 direct shear tests on rock joints of homogeneous and heterogeneous materials with three different roughness profiles. These rock joints were shaped in the laboratory with artificial stone materials, manufactured using different dosages of lime, cement and sand, obtaining samples of low, medium and high strength. The test results show that in heterogeneous materials there is a great influence of the block of rock with lower strength. In this sense, it was shown that the strength of the weak rock is dominant in the joint shear strength when there are wide strength differences between the joint faces. On the other hand, if the rock of the lower face of discontinuity is of low or medium strength and the upper face is of medium or high strength, the joint shear strength is lower than the case in which both faces are of low or medium resistance. This situation occurs for all roughness profiles, although especially in the profiles with the highest JCR. In other words, if the results were transposed to a natural slope, a homogeneous shale-type slope would be more stable than a heterogeneous one with alternating shale and limestone. The shear behaviour is also heterogeneous in the damage suffered by both faces of the joint. That is, when the heterogeneous rock blocks that, assemble the joint, exhibit a great difference in the strength, the degradation of the asperities only occurs on the side of the rock with lower strength, while the one with greater resistance remains intact.

Field-scale rock masses are discontinuous and heterogeneous in that they are composed of different sections of intact rock intersected by discontinuities. Joints are common discontinuities in rock masses that have formed previously in the rock mass's geological history. Joints can be grouped based on their orientations and other properties. When subjected to stresses, deformations occur in these rock masses. These strains either accumulate in the intact rock blocks or generate movements along discontinuities. Reproducing the stress-strain behaviour of rock masses at laboratory scale or by means of physical models is a complex task. To attempt to replicate rock mass behaviour at the laboratory scale, jointed laboratory-scale cylindrical granite samples were prepared with two different configurations of jointing. The specimens contain two smooth joint sets, forming intact rock blocks of similar sizes. Compressive laboratory tests were conducted at various confinement levels on jointed granite samples, where global deformations were measured using LVDTs (Linear Variable Differential Transformer) and corrected using energy approaches to estimate the total deformation produced in the entire jointed specimen. Furthermore, some strain gauges were fixed on the intact rock blocks to compute the localized strains in these blocks. The results of the deformations on these laboratory tests can be compared to previously conducted tests on intact rock. Based on the strain measurements of both the intact and jointed samples, it is possible to compute a preliminary estimate of the stiffness of the joints, particularly that of the sub-horizontal contacts. Moreover, the indirectly obtained local deformation values are compared to those obtained using strain gauges in order to understand the heterogeneous nature of strain in these rock mass analogue samples, which can help to better understand deformation processes of field-scale rock masses. In conclusion, this study presents the results and a first interpretation with preliminary conclusions of a set of triaxial tests conducted on jointed samples, where an estimate of the stiffness parameters was obtained based on the observed deformations on the different constituent blocks of the samples.

Rocks are natural materials and their microstructure is usually complex, involving for example voids, cracks, planes of weakness, different sizes of grains or different minerals. The micro-structural properties of the rocks influence fracture propagation, for instance, under opening fracture modes (Mode I). This paper presents fracture propagation analysis of notched rock prismatic samples tested under four-point bending conditions using a petrographic microscope of transmitted and polarized light. The two analyzed rocks are a Floresta sandstone and a Mol-eanos limestone. After testing, the sample is reconstituted and thin sections of the area sur-rounding the main fracture are obtained. The initial type of fracture (i.e. transgranular or in-tergranular), the initial deviation of the main crack and its overall sinuosity are studied to try to gain a deeper understanding of fracture processes in rocks.

Argillaceous and anhydritic rocks, along with rocks containing pyrite, are prone to swelling by adsorbing water, leading to an increase in volume or external pressure due to deformation constriction. This swelling behavior can have adverse effects on underground openings, potentially compromising their serviceability, and it can also pose a risk to structural safety. The swelling behavior of pure claystones (rocks without anhydrite) is well understood in the context of tunneling, with the swelling-strain relationship typically determined through oedometer tests conducted in laboratories. However, when dealing with rocks containing anhydrite, the processes associated with the anhydrite-gypsum transformation have only been partially explored. To gain comprehensive insights into these processes and address various related questions, additional types of tests beyond the one-dimensional oedometer tests are necessary. In this paper, we describe the setup of experiments and the corresponding testing procedure used to study the swelling behavior of rocks containing anhydrite. The results from a systematic test series serve as the data foundation for understanding the coupled mechanical and chemical processes responsible for swelling behavior. By better comprehending these mechanisms, we can enhance our understanding of the rock's behavior under various conditions and potentially improve the safety and stability of underground structures.

Crystalline rocks such as granite and gneiss, sedimentary rocks such as mudstone and clay rocks, tuff belonging to volcanic rocks, and rock salt are considered as host rocks for deep geological repository for high-level radioactive waste worldwide. In Korea, all of the above rock types are distributed except rock salt. Considering the distribution of rock types by area, granite took up 30%, metamorphic rock 30%, sedimentary rock 25%, and volcanic rock 6%. In order to evaluate the suitability of the rock types distributed on the Korean Peninsula as the host rocks for deep geological disposal of high-level radioactive waste, the Korean peninsula was divided into four tectonic structures, and then various multidisciplinary analyzes were performed with deep drilling on the four rock types of granite, gneiss, sedimentary rock, and volcanic rock. Based on the literature and information obtained from deep drilling, considering the geological and rock mechanical characteristics, granite among crystalline rocks and Jinju formation and Jindong formation among various sedimentary rocks were derived as proposed candidate rock types. For the derived rock types, multidisciplinary geological information will be obtained through additional multidisciplinary data review, analysis and further detailed investigation. This information is intended to provide basic data that can be used by high-level radioactive waste project agencies when deciding on candidate sites and rock types.

The Rhenodanubian Flysch Zone of Austria comprises cretaceous claystones, siltstones, sandstones and marly limestones. Such rock types are often referred to as weak or soft rocks due to their behaviour when exposed to water or subject to mechanical load. Even though the rock types appear quite uniform on a macroscopic level, they can exhibit a broad variety of geomechanical properties. In this study, the flysch rocks were investigated with respect to their slaking durability, uniaxial compressive strength, abrasivity and mineralogical composition. The influencing factors affecting material behaviour and correlations of different mineralogical-petrographical and rock mechanical parameters are elaborated. It is shown that granulometric and mineralogic properties correlate well, and that the presence of carbonate minerals can favour the slaking resistance. Sheet silicates seem to affect slaking only after many testing cycles. While the rocks exhibit a wide range of slaking durability and low to moderate strength, abrasivity is limited to low values. Unlike in crystalline rocks, quartz imposes less influence on durability, abrasivity and strength. The correlations of engineering rock properties of these soft rocks are weaker compared to those of grain bound crystalline rocks making their characterization and classification challenging.

Stress polygons defined by the Coulomb failure criterion play an integral role in earth sciences and geology for the classification of crustal stress regimes. While the minimum principal stress (σ3), pore pressure, and friction angle of the rock considerably influence rock strength, the intermediate principal stress (σ2) also plays a crucial role. In conventional stress polygons, the boundaries of rock strength are represented by straight lines based on the Coulomb failure criterion. However, when considering σ2, these boundaries should ideally be drawn as curved lines. In our study, we redefined the stress diagram by involving σ2, using true triaxial test results and the Mogi–Coulomb failure criterion. This approach revealed notable visual discrepancies in rock strength boundaries compared to those defined by traditional Coulomb failure criterion. Our findings underscore the importance of incorporating σ2 in failure criteria to accurately draw rock strength in stress diagrams.

A series of laboratory tests have been performed to assess the effects of progressive de-formation on the elasticity and compressive strength of the VQ rock sequence. Specimens of basalts and pyroclastic rocks were obtained from twelve boreholes drilled with depths between 40 and 160 m. UCS tests were performed on a highly stiff and fatigue-rated load frame model MTS 815. Specimens were subjected to increasing-amplitude cyclic loading experiments. Changes in the elastic properties were observed in both sedimentary and vol-canic rock types as the rock approached the rupture. A significant difference in strength was obtained, with UCS values ranging between 13.5 and 23.97 GPa for the basalt, and be-tween 0.96 and 1.27 GPa for the pyroclastic sequence. Our results suggest that the differ-ences in stress failure may explain the debilitating nature of the contacts between basalts and pyroclastic rocks that might explain ground ruptures.

Mode I fracture toughness (K_IC) is one of the most important parameters for predicting and preventing catastrophic failure of cracked structures in brittle material. Several laboratory methods have been suggested to determine the mode I fracture toughness. However, many of them require lengthy sample preparation procedures, premature failure of samples, and difficulties in obtaining the precise value of the fracture toughness property. In this paper, the recently proposed pseudo-compact tension (pCT) method is used to evaluate the crack length effect on mode I fracture toughness in an isotropic homogeneous material, benefiting the advantages of this method including; simplicity of the test, high level of test control and high accuracy of the K_IC value. For this purpose, several disc shaped PPMA samples were loaded in pure tension by performing pCT tests. Digital image correlation (DIC) method was utilized to assess and monitor the distribution of the deformation field during the tests. DIC results were also used to compare the effect of crack length on the deformation field variation in samples. Very good agreement was found between the K_IC values estimated in this study and those reported in the past for the similar material; indicating that the pCT method is convenient for the assessment of K_IC. The experimental results also show that the initial crack length has a net impact on K_IC, although the magnitude of its influence is closely related to material structure and type. According to the obtained results, an increase in the initial crack length leads to increase the ultimate displacement at failure point, decrease the maximum load, and finally decrease the mode I fracture toughness of the material.

The Great Glen Fault (GGF) of Northern Scotland is one of the most enigmatic fault structures in the UK. Despite much previous work, its status, longevity and movement history remain controversial. The British Geological Survey (BGS) are currently undertaking a nationwide project aimed at characterising major faults in the UK. ‘UK Structure’ aims to generate a baseline dataset that will meet the needs of various stakeholders requiring information about faulting history and properties in the UK and its impact on national infrastructure, groundwater resources and geodisposal, for example. The Coire Glas project is a hydro pumped storage scheme with the capability to double the current electricity storage capacity of Great Britain. The ambitious and large-scale civil engineering project will involve tunnelling through the GGF in order to connect the lower reservoir (Loch Lochy) with the new upper reservoir. Detailed characterisation of fault rocks encountered during the project will help to better understand the GGF, and has potential implications for future engineering projects. Here we have devised and applied a characterisation workflow to a suite of fault rocks from the GGF. The workflow includes the application of CT during sample preparation, allowing for preparation of an undisturbed and fully orientated section of fault gouge material. Furthermore, detailed petrology of fault rocks is determined using a range of methods including X-ray Diffraction (XRD), optical microscopy (OM), scanning electron microscopy (SEM), and optical (cold-cathode) cathodoluminescence (CC-CL). The microstructure of the fault rocks reflects a complex multigenerational fracturing history associated with movement on the GGF, indicated by numerous different phases of carbonate and silicate mineralisation as identified using SEM Mineralogic software. These phases include Mg-siderite cements within fault gouge, and late-stage authigenic kaolinite and calcite cements within fractured ferroan dolomite clasts. In addition to detailed petrological characterisation, we intend to carry out U-Pb dating of calcite crystals within fault rocks to determine the age of calcite mineralisation, thus providing a better understanding of the timing of fault movement.

Localised failure in the form of shear localisation bands is always observed in triaxial tests on rocks and other geomaterials. The deformation inside a shear band is usually much higher than its counterpart in the zone outside the shear band, while stresses inside and outside a shear band are comparable, due to equilibrium conditions across the boundary of the shear band. Inelastic behaviour of the specimen is mainly governed by the behaviour inside shear bands and hence should be considered as true intrinsic properties of the material. Nevertheless, traditional practice in analysing and interpreting triaxial test data usually ignore localisation of deformation by taking averaged measurements of both strains and stresses over the volume of the specimens. As a consequence, the use of stress-strain relationships obtained from triaxial tests to represent behaviour of geomaterials is questionable, given they are the averaged quantities and hence cannot truly represent intrinsic properties of rocks and other similar geomaterials. In this study, an approach considering localised failure is developed and used to correctly interpreting and analysing triaxial test results on rocks. The obtained results on stress and relative displacements between two sides of a shear band are considered intrinsic post-localisation behaviour of rocks. They can be used directly for the development of a new generation of constitutive models taking into account localised nature of failure. Both benefits and practical implications of the proposed new approach for obtaining intrinsic properties of geomaterials are discussed and highlighted.

The Capo d'Orlando is a terrigenous formation outcropping in the northeastern part of Sicily (southern Italy). Its deposition is related to the preliminary erosion of basement metamorphic rocks, and subsequent transport through gravitational processes in different sedimentation ba-sins. This led to the formation of heterogeneous deposits consisting in sandstone banks, locally alternating with pelitic and conglomeratic layers. The present research aims to study the sand-stones at the scale of both intact rock, that was analyzed in laboratory to assess their physical - mechanical properties, and rock mass, through field surveys. The achieved results confirmed that although the sandstones are part of the same geological formation their physical-mechanical features are strongly variable.

Heritage conservation is of great importance to society, particularly in light of the recent increase in fires affecting historical buildings. This study investigates the effects of high-temperature exposure on Pedra de Borriol, a specific type of limestone. This rock has been commonly used in the construction of historical monuments in eastern Spain since the 17th century, and it continues to be utilized today, particularly for ornamental purposes. The study analyzes the effects of high temperatures on the strength, mineralogy, and color of this cretaceous limestone. On one hand, it is known that the strength of rocks decreases with increasing temperatures when subjected to thermal treatment. In the case of the limestone studied in this research, a decrease in strength of over 90% has been observed when exposed to temperatures exceeding 800°C. On the other hand, it has been noted that the color of this rock varies noticeably at different temperatures. The significant color changes are directly linked to the mineralogical composition of the rock. At an exposure temperature of 400°C, the natural color of the rock turns reddish; at 600°C, the color becomes gray, and at 900°C, the rock exhibits a whitish coloration. By considering the three aspects of mineralogy, color, and strength, it becomes possible to assess the impact of a fire on a historical monument constructed with this particular rock. Through this analysis, it is possible to (i) estimate the maximum temperature the material has been exposed to, (ii) evaluate the decrease in strength using non-destructive testing methods such as color changes, and (iii) identify the areas of the building affected by varying degrees of thermal damage. The ultimate objective is to investigate the effects of high temperatures on both the ornamental and structural functions of the rock. The results obtained from this research contribute to the advancement of techniques for assessing thermal damage to historical heritage after a fire

This study delves into the utilization of an innovative numerical modelling approach to investigate the impact of reinforcing pillars on their strength and stability. Existing case studies in the literature have demonstrated that various methods such as tendon installation, pillar strapping, and the application of shotcrete or thin spray-on liners are commonly employed for pillar reinforcement. However, there is a notable absence of a well-defined methodology for selecting the appropriate support type or determining the necessary support capacity. Consequently, despite the implementation of substantial support measures, certain mines continue to experience pillar collapses. The impact of pillar confinement on a mine wide scale can be analysed thanks to a limit equilibrium model, that was built into a displacement discontinuity boundary element program. The model that incorporates confinement along the pillar's perimeter to replicate how the support interacts with a failing pillar. As part of this study the effects of confining a pillar were analysed and are shown to accurately predict that increased confinement results in a reduced extent of pillar failure.

A comprehensive geotechnical investigation program including geophysical well logging was implemented at an iron ore deposit in Uzbekistan, which targeted at gaining parameters for resource/reserve estimation and mine planning. The deposit represents an asymmetric, approximately ellipsoidal elongated body of about 4.5 by 1.8 km in size. The ore body of vanadiferous titano-magnetite-rich clinopyroxenite is surrounded by metasedimentary strata that form a north plunging synclinal structure, and crop out at three sides of the deposit. Evaluation of the obtained geotechnical data revealed that the project site is generally characterized by significantly varying rock mass conditions. Host rocks are inhomogeneous, foliated and the mechanical properties are directional. The different strata of the surrounding metasediments show high diversity of rock mass properties. For the evaluation of the pit slope stability, kinematic as well as deterministic and probabilistic analyses and a sensitivity analysis were made. In addition to the investigation of potential block failures along discontinuities in the benches, numerical modelling was conducted for the overall pit slopes to evaluate final pit wall stability in the design sectors and assist the mine planning and optimization. It was found that the maximum possible final pit wall angles depend less on the conditions of the ore body rock mass, but essentially on the metasedimentary rocks and dip at the syncline outlines. In contrast, a much steeper overall slope angle that can reach up to the maximum single bench angle would be possible in the north, if leaving a safety pillar of stronger pyroxenite in the slope wall to prevent sliding in the thick Alluvial cover sediments. Based on the findings the mining plan was developed, which included as main tasks the selection of the most suitable mining concept, a pit optimization analysis, mine layout design, mine sequencing, long-term production scheduling, and mine equipment selection.

Early determination of jumbo drill performance is crucial for selecting appropriate mining and civil engineering equipment. Quick and simple laboratory tests are needed for accurate predic-tions of on-site drilling rates. The Sievers’ J-miniature drill test represents thrust and rotation in a rotary-percussive drilling process. Continuous monitoring of drill penetration in these tests provides valuable information on penetration rate–time plots. In our study on sandstones and limestones from an Asturias mining site, miniature drill tests reveal two distinct periods in pen-etration–time curves: an initial period with a peak attributed to drill bit adjustment and a subse-quent stable period, offering a realistic representation of material drillability. Comparing labor-atory test results with jumbo drill performance in the same lithologies opens a new possibility to predict jumbo drill performance.

Úcar's criterion establishes a correlation between the principal stress axes during failure and the compressive uniaxial strength as well as the tensile strength of the rock. Consequently, it can be employed in the "prediction mode" during the initial stages of a project to determine the parameters for the resistance equations using simple compression and tensile tests (such as Direct Tensile or Brazilian tests), yielding a reliable estimate (with a confidence level of over XX%). As the project progresses to more advanced stages, it is generally recommended to conduct triaxial tests on specific rock units. In such cases, Úcar's criterion demonstrates a remarkably accurate fit. This study explores both aspects of Úcar's criterion, utilizing literary and experimental triaxial test datasets (over one hundred independent data sets, covering a wide variety of rock types) to evaluate the level of data fitting achieved. Furthermore, a similar analysis is conducted using the Hoek-Brown criterion, allowing for a comparative assessment of the performance of both criteria. From the analysis of the results it can be seen that the Úcar's criterion, used to predict the rock behaviour (i.e. with uniaxial tests and stresses), compares favourably even with the use of the H-B equations in adjustment mode (i.e. with triaxial tests).

This research studied the size effect and anisotropy of shale strength under polyaxial compressive stress conditions through laboratory experiments. Firstly, this research designed an in-house polyaxial compression test setup, which included a uniaxial compression test machine, biaxial platens, and confining devices. Secondly, this research prepared cubic shale specimens at the sizes of 25.4, 50.8, and 76.2 mm and orientations of 0, 45, and 90°. At last, this research conducted the uniaxial, biaxial, and triaxial compression tests on these specimens. The test results shows that the strength presents a decreasing trend as size increased irrespective of specimen orientation and stress condition. The anisotropic behavior of strength is unaffected by specimen size, but it varies as the stress condition changed. This transition is due to the second principal stress, which has a noticeable effect on the failure mode of shale and leads to the change of strength anisotropy.

Permeability around faults varies locally due to the existence of damage zone and clayey fault cores that experienced deformation and fracturing. Therefore, proper assessment of local changes in permeability around fault is recognized as an important research area for geoengineering applications such as radioactive waste disposal and carbon sequestration and storage. We developed a simple permeability testing device to measure the distribution of hydraulic conductivity around faults. The key advantage of this equipment is its porta-bility and simplicity, allowing on-site measurements. First, we used this equipment to measure the hydraulic conductivity on the standard rock samples and compared the results with data obtained from conventional laboratory hydraulic conductivity tests. Thereafter, we applied this approach to rocks containing faults to study the characteristics of hydraulic conductivity around faults.

The Callovo-Oxfordian claystone (COx) is an anisotropic rock formation that serves as the host for the envisaged deep geological repository for intermediate-level and high-level long-lived radioactive wastes in France. In this context, the construction of several T-shaped gallery intersections is a common technique used for accessing the surrounding cells. In this work, a numerical analysis of a T-shaped gallery intersection excavation at great depth in the COx claystone is presented. A Drucker-Prager elastoplastic constitutive law with shear strength hardening is used to describe the rock matrix and the inherent anisotropy is implemented using the fabric tensor approach. Simulations include galleries with circular cross-sections intersecting at a normal angle. The focus lies on the mechanical characterization of the zone around the intersection. The results highlight the plastic strain distribution around the main gallery walls. Furthermore, the extension of the plastic zone is presented.

This paper proposes an analytical approach for analyzing rock slope stability based on a three-dimensional (3D) Hoek-Brown (HB) criterion to consider the effects of 3D stress and strength. The 3D HB criterion, considering an associate flow rule, is utilized to describe the perfectly-plastic behavior of rock mass under a plane strain condition. To reflect the change of friction angle on the failure surface, the potential failure surface (PFS) is divided into small segments with each segment being assigned a unique friction angle. The upper bound theorem of limit analysis is combined with the strength reduction method to determine the factor of safety (FOS) of a rock slope with a defined PFS. By optimizing the PFS, the minimum FOS and the critical failure surface (CFS) of the rock slope are obtained by the customized genetic algorithm. The proposed approach is validated by comparing it with an HB criterion-based solution and numerical simulations. Parametric studies are also performed to investigate the effects of rock mass properties, slope geometry, and loading conditions on the FOS and CFS. The results indicate that ignoring the 3D stress and strength of rock leads to underestimation of FOS and it is important to consider the various factors when evaluating the stability of a rock slope. For the effortless application of the proposed approach, a Python-based graphical-user-interface application is developed as a stand-alone executable app and is successfully applied to analyze a rock slope.

Dionyssos marble quarry is located 30 km from Athens and it is an important quarrying site in Greece. Apart from standard commercial purposes, it is also used for the restoration of the Parthenon as it is part of the same marble deposit that was used for the construction of Athenian Acropolis monuments in the 5^th century B.C. The Dionyssos marble is a fine-grained metamorphic marble exploited partly open-pit and partly underground. The modern times exploitation started in 1949. The increased demand for ornamental stones has led to intensive exploitation of the existing marble quarry. The gradual depletion of surface deposits is a direct consequence of this increase. For this reason, the company proceeded to exploit part of its deposit using underground methods, which have the added advantage of minimal environmental footprint. By applying the method of room and pillars, openings up to 15 meters wide are achieved, while the maximum height of the rooms is 30 m. In this research the future underground development is considered. It is envisaged at the higher level of the two existing underground openings and will consist of five rooms in the North-North-West direction excavated in six stages and two rooms in the North-North-East direction excavated in twelve stages. Support measures only include resin rockbolts of length adapted to pillar or roof installation. A set of advanced numerical simulations of the room and pillar gradual development and support is performed using a different numerical scheme for the evaluation of the stability; the distinct element method is used so as to include the effects of macro-discontinuities affecting the stability of the pillars during the top-to-bottom development of the marble extraction. Extensive laboratory tests have been performed on rock samples and the effect of scale on the peak compressive strength is also taken into consideration. The results of the analyses have shown that the stability of the exploitation is secured for the specific underground development.

The swelling of anhydritic rocks is responsible for severe damages to numerous tunnels. Alt-hough the first problematic cases were recorded more than a century ago, there are still knowledge gaps concerning the swelling behaviour of anhydrite, which introduce uncertainties in tunnel design. A major uncertainty relates to the magnitude of the developed strains due to the anhydrite to gypsum transformation, which depends inter alia on how gypsum crystals will grow. The latter may be influenced by the porosity, specifically whether the new crystals will grow within the available pore space or push the particles apart causing expansion. This paper investigates this effect by means of experimental tests conducted on artificial specimens of an-hydrite and kaolin powders. It is shown that, ceteris paribus, the strain developing during the anhydrite to gypsum transformation decreases with increasing initial porosity. The presented experimental results are valuable for better understanding of the observed phenomena.

The unloading disturbance during the excavation process in rock masses can significantly affect the safety of deep underground structures, especially when encountering rock frac-tures. In this study, the unloading process of normal stress was conducted using three dif-ferent levels of unloading rates. Simultaneously, the acoustic emission (AE) technique was employed to monitor the growth of microcracks at the interface. The recorded AE count, AE energy and calculated AE b-values were compared with the evolution of stress and displacement to confirm the correlation between AE signals and unloading behaviour. The experimental results revealed that the stress state associated with a low unloading rate is closer to the failure envelope compared to high unloading rates. During the unloading pro-cess, the maximum AE count, the highest AE energy, and the sudden decrease in b-value can serve as indicators that facilitate short-term prediction of failure sliding.

Explosive-free rock breakage methods have been the subject of increasing research in the past three decades as they are considered more environmentally friendly than traditional rock fragmentation with explosive energy. This paper summarizes the results of research findings on rock breakage with expansive cement, also known, soundless chemical demolition agents. Expansive cement is a powdery material that expands upon curing in a borehole causing it to eventually fracture. Expansive cement is a commercially available product that is usually used in the construction industry for the demolition of concrete foundations. Only in recent years that interest in the use of expansive for mining applications has been on the rise. Some of the challenges faced with the use of expansive cement are 1) rock is considerably stronger and stiffer than concrete, 2) rock is subjected to confinement in-situ, and this would inhibit the breakage mechanism by limiting the expansion, and 3) expansive cement does not work well in cold climate conditions, which are frequently encountered in Canadian surface mines. This paper summarizes the results of experimental and numerical studies conducted to estimate the peak expansive pressure and its variation with host medium stiffness. Direct pressure measurement is used to validate the classical analytical method employed for pressure estimate using instrumented thick-walled steel cylinders of different expansive cement borehole diameters and wall thicknesses. A series of rock slabs from Stanstead granite is then tested with a central hole injected with expansive cement and subjected to uniaxial compressive stress of 5 MPa. The results are compared with those obtained from unloaded rock slabs. Expansive cement breakage performance is measured by the time of first fracture (TFC) and the minimum demolition time (MDT). Another series of tests examined the potential benefits in terms of TFC and MDT of a relief hole (empty hole) in the vicinity of the injected hole under uniaxial pressure. Finally, an Extended Finite Element (XFEM) of the granite slab with expansive cement borehole is built with Abaqus software to help estimate the appropriate spacing between EC holes to achieve fragmentation. The results are used as design guidelines for rock fragmentation of boulders and uniaxially loaded pillars in the field.

Discontinuity flow behaviour in fractured rock mass remains a challenge in rock mechanics. This is due to fluid path prediction and velocities through the unsaturated zone under changing moisture conditions. This study proposes using the rock engineering systems (RES) approach to examine the interaction of the principal parameters in assessing discontinuity flow behaviour in fractured rock. This is achieved by a soft approach 3×3 interaction matrix in which the leading diagonal of the matrix is partially saturated flow, discontinuities in the fractured rock mass and the application of infrared thermography and photogrammetry. A georeferenced photogrammetry model is employed for 3D geotechnical discontinuity feature extraction. The analysis of these interactions shows that partial saturation in fractured rock mass depends on the discreet fractures, fracture network connectivity and matrix influence on storage. The leading diagonals of this RES approach highlight the most critical parameters for partially saturated discontinuity flow behaviour in fractured rock.

Fluid flow shows different behaviors through rough fractures with different scales. Numerical study as a powerful tool can be used to simulate fluid flow through a fracture with different scales. Geometrical properties, such as physical aperture and roughness, are important factors that have to be measured precisely. Photogrammetry, as a high-precision technique, was hired to reconstruct three-dimensional (3D) model of a granite fracture with a dimension of 25 cm × 25 cm × 10 cm. A high number of markers and scale bars were used to scale and orient the 3D model of the fracture accurately. The obtained 3D model of the fracture was used to simulate fluid flow behavior in a rough rock fracture. To validate the numerical modeling, experimental hydraulic tests were conducted with different hydraulic gradients ranging from 20 (kPa/m) to 200 (kPa/m) with an interval of 20 (kPa/m) under 0.3 MPa normal stress condition. Then, the obtained 3D model was used to simulate fluid flow through the fracture in different side lengths of 5 cm, 10 cm, 15 cm, 20 cm and 25 cm with the same hydraulic gradients. The results showed that the relationship between the hydraulic gradient and the flow rate was nonlinear and followed the Forchheimer Equation. The obtained hydraulic apertures were normalized to the subsample size lengths and were compared together. The results show the normalized hydraulic aperture decreases by increasing the sample sizes.

The analysis of the stability of rock slopes requires studying both the rock mass and the discontinuities within it. Discontinuities are typically considered planar at a reduced scale of study, usually on the order of meters. Furthermore, they tend to occur in sets with similar orientations. The characterization of these sets decisively influences the stability of the rock slope, making their study a key component. Traditionally, manual methods (compass, clinometer, measuring tape, etc.) have been used to collect data on the rock mass. However, this data collection is subject to operator subjectivity, potential hazards from falls or rockfalls, or even weather conditions. In this regard, the use of remote sensing techniques such as terrestrial 3D laser scanning or digital photogrammetry with RPAS (Remotely Piloted Aircraft Systems) has acquired popularity and acceptance within the scientific community in the last decade. Terrestrial laser scanning (TLS) is highly accurate and has been extensively used to geometrically characterize slopes. However, this instrumentation has the limitation that measurements are taken at ground level. Some areas of the slope may not be observable from the ground, thus limiting the surface that can be scanned. The popularization and accessibility of RPAS have enabled their widespread use in digitizing rock slopes using Structure from Motion (SfM), allowing for the reconstruction of surfaces in areas that cannot be digitized with TLS. However, the accuracy of this technique is lower compared to TLS. This research proposes the digitization of slopes using RPAS and airborne 3D laser scanning, with a comparison to data acquired with TLS assuming that the TLS data is correct. The study involves obtaining families of discontinuities using both techniques, and the comparison will allow for a discussion on whether the achieved level of accuracy and resolution are sufficient for addressing the geometric study of the discontinuity families. Two case studies are presented in the province of Alicante, Spain, analyzing the discontinuities in subvertical Cretaceous marls and another outcrop of Alicante Miocene.

Discontinuities significantly impact the stability of a rock mass and its hydraulic conductivity. Therefore, mapping rock discontinuities is essential to study rock mass behavior. This study explores the use of videogrammetry for digitizing rock mass at the tunnel face and measurements of joint orientations. Utilizing a mobile device for video capture, the method is compared against traditional laser scanning and mobile photogrammetry. Videogrammetry allows rapid data collection with smartphones or action cameras, emphasizing low-cost and accessibility. Results indicate that videogrammetry with a smartphone pro-vides an acceptable level of 3D reconstruction, with 3 mm control distance error and 1 cm cloud-to-cloud distance compared to a reference high-resolution laser scan. Discontinuity orientations measured from the videogrammetric 3D model show reasonable errors of less than 2-6° on average compared to data measured from the reference laser scan. The study validates videogrammetry as a practical, efficient alternative for rock mass characteriza-tion in underground settings.

Advanced geological prediction in tunnels primarily focuses on the weak layer, identified by shear wave velocity. Traditional methods using longitudinal and transverse wave velocities have low accuracy due to ambiguities. Surface waves offer a more precise alternative, though "mode kissing" during dispersion can cause misinterpretations, increasing construction risks. We propose a novel model-substitution method to invert weak layer models and spatial measurement data from tunnels, improving prediction accuracy. Our approach, validated by comparing with advanced drilling results, effectively inverts velocity structures of weak layers, offering a new method for geological prediction using surface-wave and reflection-wave techniques.

The old Grohovo rock avalanche, near the City of Rijeka, Croatia, was activated in 1870 and reactivated in 1885 after prolonged heavy rain period. In its reactivation this rock avalanche of about 16 Mm3 buried 7 houses in its foot. The dimensions of the landslide are length of 490 m, width of 810 m and the slip surface depth of about 85 m. The landslide is situated at the Rječina River Valley slope built in siliciclastic flysch deposits in the bottom and limestone rocks at the top of the valley slopes. The slip surface passes through limestone rock mass at the top of the slope and through flysch rock mass in the lower part of the slope. The Grohovo rock avalanche, the most probably dormant landslide in the last 140 years, was never deeply investigated. In this manuscript, preliminary results of landslide mechanism based on remote sensing surveys are presented. Based on analysis of these data, the landslide model is estab-lished and its activity in the last 70 years was estimated.

The understanding of preparatory processes like thermo-mechanical deformations in charge of natural and man-made rock slope stability strongly condition the efficiency of triggering actions. i.e., rain- and snowfalls, dynamic vibrations, blasts which can operate as near-surface processes. In this sense, the qualitative understanding of preparatory and triggering factors is often limited to qualitative register, and limited is the knowledge about the role (single or in combination) of the environmental conditions that contribute to the occurrence of rock failures (mostly falls and sliding) in critical and subcritical regimes. To achieve the general objective to predict timing and location of ultimate failures in rock walls and quantitatively assess cause-to-effect empirical relationships, an experimental site integrating geotechnical and geophysical monitoring is active since 2016 in Central Italy in an abandoned quarry, namely the Acuto Field Lab managed by the “Sapienza” University of Rome. The Acuto Field Lab acquisition focuses on i) full monitoring of weather conditions and rock strain acquisition by strain gauges and joint meters; ii) 3D InfraRed Thermographic monitoring and contact thermal monitoring, iii) seismic noise measurement devoted to assessing permanent changes in physical and mechanical parameters, iv) Acoustic Emission (AE) and Microseismic (MS) event detection as precursors of incipient failures. The data collected to date supported, in an analytical stage, the numerical quantification of inelastic deformation occurrence in rock mass under periodic forces through stress-strain modelling. The main outcomes focused on the effect of temperature changes over the rock surface and across joints, highlighting the response of major rock fractures and microcracks to the experienced temperature fluctuations at different depths (i.e., thermally active layers). Geophysical monitoring registered the dynamic response of the exposed rock wall under daily and ordinary thermal cycles and a non-ordinary weather event, highlighting, as preliminary results, the occurrence of acoustic emissions as effect of cooling relaxation. Under intense weather events that caused fast freezing, low-frequency MS signals have been attributed to different driving mechanisms caused either by thermal dilation or contraction and by freezing-thawing mechanisms.

Detecting displacement trends is critical in engineering geotechnics to prevent structure collapse, especially in mining operations where monitoring ground movement is vital. Tailings Storage Facilities (TSF) store mining by-products, posing risks of dam collapse. Limited global data makes TSF management complex, accentuating the need for rigorous monitoring. Rio Tinto, collaborating with Atalaya Mining and CSIC, aims for a digital transition to enhance geodetic and geotechnical monitoring. Utilizing Hexagon GeoMonitoring Hub (GMH) platform, data from various sensors are integrated for comprehensive analysis. This strategy allows to detect a slow movement estimated on average at 1 mm/month; the correlation between the data made it possible to understand where the movement is located (with a different displacement trend from the top to the bottom portion), the direction of movement and the structural discontinuities of the dam. This study presents insights for future modeling and best practices in mining and civil engineering monitoring, benefitting structures like road slopes and water dams.

In November 2022, near the village of Castrocucco di Maratea (PZ), a severe rockfall, over 5000 m3 of dolomitic rocks, affected the national road n. 18 ”Tirrena Inferiore” at Km 241+600, whom surveillance and manutention are operated by ANAS spa (Gruppo Fs Italiane), the Italian leading Concessionaire of national road and motorway network. In the 25 Km section between Sapri and Castrocucco di Maratea, the road is a very tortuous, panoramic and tourist itinerary with a two-lanes single carriageway. The road is “carved” in intensely fractured and karst rock cliffs subjected to fast landslides. The route is the only national road serving a critical seaside tourist area and provides a direct connection between the coastlines of Campania, Basilicata and Calabria regions. The rockfall of November 2022 started as a major planar sliding developed on a low-angle fault and triggered by the intense rains of the preceding month. It destroyed part of the road with complete collapse of the retaining structures, fortunately with no fatalities nor injuries. As a consequence, the road had to be closed, and an alternative viability was instituted. However, the road needed to be reopened before the start of the approaching summer season. ANAS SpA, in cooperation with other national and local authorities, accomplished to rebuild the road body and to mitigate the hazard. On the 14th of July the road was temporarily reopened up to the 30th of September 2023, with traffic restrictions. To enhance traffic safety and ensure the functionality of the protection structures, ANAS activated the onsite surveillance and implemented a remote real-time monitoring activity of the slope movement integrated with automatic real time early warning systems. The monitoring points were defined following a structural analysis of the fracture system. The latter was performed by means of field surveys and remote analysis via Virtual Outcrop Models (VOM) developed after image acquisition via drones. This system consists of automated topographic measurements integrated with a meteorological station and remote-controlled security cameras. Furthermore, inclinometers and strain gauges are installed on the rock slopes. A Virtual Machine Service (VMS) receives the monitored data via a wireless system. The software identifies settlements and/or displacements that exceed the threshold limits and sends an e-mail alert. This article presents the monitoring system made to prevent or reduce risks in case of rock mass deformation and consequent rockfalls, showing how early warning could play a significant role for a safe road management.