In the present paper, statistically significant correlations are obtained between sample di-mensions: height H, width W, and length L, on one side, and compressive strength σp and resistance to cutting KL of the clay sample, on the other side. The geomechanical proper-ties of the coal overburden are determined in laboratory conditions. Coal overburden has a predominantly clayey-silty composition, and samples were taken from the Tamnava East-ern Field (Serbia). Laboratory data are analyzed using multiple linear regression. Results obtained indicate the existence of statistically significant correlations between sample sizes and both σp and KL. These correlations are presented in the form of explicit nonlinear mathematical expressions with corresponding diagrams, which enable further quantitative and qualitative interpretation of the mutual interaction of the analyzed geometrical and ge-omechanical properties. Obtained correlations are with high values of the determinism co-efficient (R > 0.9) and low values of standard deviation. Results are further verified using the ANOVA test. Critical values for certain sample dimensions regarding their effect on σp and KL.

When using the calculation of stability (regardless of the methodology that is being used), there are two approaches: deterministic and stochastic. The first prerequisite for any calculations is that there are enough data that can be processed statistically - to satisfy the Student classification. When using the deterministic method, the main value to be taken into account in the calculations is the mean value, whereas when using stochastic calculations, all the results obtained by laboratory or field examinations are equally represented. Thanks to this, non-homogeneity of the massif has been introduced to the calculations. This paper presents the methodology of stochastic calculations, and shows one example of comparative analysis of the results of stochastic and deterministic calculations

The stability analysis of rock slopes holds paramount importance in a multitude of geotech-nical projects, including rock-fill dams, embankments, as well as natural and excavated slopes. Among the various failure modes encountered in rock slopes, planar failure is a significant concern. Numerical analysis employing the Mohr-Coulomb linear criterion is a conventional approach adopted by engineers to evaluate the likelihood of planar failure within rock slopes. Nevertheless, the shear strength behavior of rock masses is universally recognized to exhibit nonlinear characteristics, rendering the Mohr-Coulomb criterion a simplified representation of a more complex reality. To bridge this gap, a range of nonlinear shear strength criteria has been formulated, aiming to more accurately depict the nonlinear behavior of rock masses. The objective of this paper is to provide novel insights into the stability analysis of rock slopes through the application of the Úcar nonlinear criterion. The outcomes demonstrate that the Úcar criterion, when juxtaposed with other nonlinear criteria reported in scholarly literature, provides a more precise estimation of the potential failure wedge.

Carbonate rocks have been widely used as a building material in architectural and civil engineering works due to their great availability and beauty. These geomaterials are frequently exposed to acidic aqueous conditions in outdoor environments that can reduce their durability. This study investigates the impact of immersion in acidic aqueous solutions prepared from hydrochloric acid on the physico-mechanical behaviour of a porous limestone from Alicante (Spain). For this purpose, physical characteristics (colour, density, porosity, P- and S-wave velocities and associated dynamic parameters) and mechanical properties (uniaxial compressive strength and Young's modulus) of limestone samples were determined in its initial intact state and after immersion for one month in acid and neutral solutions with pH values equal to 2, 4 and 7. The results revealed that the exposure of the limestone to the acid solutions increases its porosity and reduces its density, P- and S-wave velocities, uniaxial compressive strength and Young´s modulus, which can be attributed to the hydro-physico-chemical interactions between the minerals of the rock and the pore fluid. The knowledge obtained can serve as a basis for determining the suitability of the use of the studied building rock in acidic aqueous environments such as those generated by acid rain or bio acid attack (e.g., lichens) and for establishing the preventive conservation actions to be conducted in heritage constructions built with this stone.

In many fracture mechanics tests, starter notches are commonly carved in samples to generate a small-size region with high-stress concentration in a precise location of the sample of interest. Contrary to other materials where fatigue pre-cracking is possible, starter notches had to be cut in rocks. A variety of techniques exist, but the most common way is to use sawing or milling techniques. Leaving aside the requirements of precise alignment of the notch with respect the specific geometry of the sample and stress orientation, the intrinsic properties of the notch (e.g., sharp or blunt, thick or thin) likely affect the shape and extent of the fracture process zone (FPZ) ahead the crack tip and the fracture toughness (K_C) itself. In this contribution the effect of cutting a relatively thick (~1 mm using a diamond saw disk) and thin (~0.3 mm using a diamond saw wire) starter notch in 4 distinct rock types with apparent macroscopic homogeneity: Moleanos limestone, Floresta sandstone and Macael and Carrara marbles is analyzed. In the two cases, the shape of the edge of the notch is blunt but with a different radius of curvature. Samples were characterized in advance of testing (V_P & V_S, X-ray micro-FRX) to evaluate the homogeneity of the specimens. Then, fracture toughness tests (12 samples per rock type: 6 with the thick and 6 with the thin notch; 48 samples in total) have been performed using the pseudo-compact tension (pCT) technique, which is intended for the precise assessment of this property in mode I (tension). Some of the tests were also complemented with Digital Image Correlation (DIC) observations focused in the FPZ region. Results show that macroscopic (de visu) homogeneity criterion is not enough to guarantee homogeneous mechanical results. With respect the effect of starter notch thickness, we observe that, within uncertainty, there is no significant difference in K_IC (in MPa m^½) in the case of the Floresta sandstone (thin notch = 0.40±0.01; thick notch = 0.37±0.01) and the Macael marble (thin notch = 1.03±0.04; thick notch =1.07±0.06) while that difference is a little bit more significant in the case of the Moleanos limestone (thin notch = 0.85±0.05; thick notch = 0.93±0.03) and, especially in the case of the Carrara marble (thin notch = 0.75±0.05; thick notch =0.93±0.05).

The historic center of Salobreña (Granada, Spain), is located on the summit of a 100-meter-high promontory of Triassic marbles rock known as “La Peña del Castillo”. In this area, rockfalls of different magnitudes have occurred, some of them at the foot of Salobreña Medieval Castle. Recent events in November 2019 and June 2022 have caused significant social alarm due to their impact on the access roads and assets. Fortunately, there were no reported fatalities. To evaluate the fracturing of rock massif, data from discontinuities families were col-lected using (1) geomechanical in-situ stations, as well as (2) applying remote sensing techniques like LiDAR, and another tools, more cost-effective and accessible than LiDAR instrumentation, that combines drone flights and the application of Structure-from-motion (SfM) technique. After applying each technique individually, the discontinuity families have been evaluated and combined.

Factor of safety (FoS) procedures while using finite element methods (FEM) require stable calculation models. When FoS < 1 this condition is not verified, and the safety analysis cannot be completed. An alternative approach is presented to determine the factor of safety for unstable rock slopes, considering the Hoek-Brown (HB) failure criterion and using Plaxis 2D software for the calculations. The proposed methodology defines a modified HB material with better properties than the original, by applying an upgrade factor in its yield function. Then, FoS ≥ 1 is now obtained by calculating with the improved material, and FoS of the original material would be the result of dividing the FoS of the improved material by the corresponding upgrade factor. Various materials are required to calculate the same FoS to improve the accuracy of the results. The proposed methodology has been tested with a rock slope example for different material conditions.

Phyllite is a type of metamorphic rock characterized by its fine-grained, foliated structure, resulting from the low-grade metamorphism. Its mineral composition mainly comprises mica, quartz and chlorite. The exceptional mechanical properties and geological features of phyllite render it a key factor in slope instability. The primary geotechnical concern associated with phyllite is its pronounced cleavage planes, which can act as potential slip surfaces during slope failure. These cleavage planes are zones of weakness that facilitate the initiation and propagation of landslides and slope movements. Furthermore, the presence of phyllite can intensify the susceptibility of slopes to failure. The weathering characteristics of phyllite further contribute to slope instability. Over time, phyllite undergoes chemical and physical weathering, leading to the formation of clay-rich soils and alteration of the rock's mechanical properties. These altered materials can act as lubricants along cleavage planes, reducing the frictional resistance and promoting landslide events. The A-7 highway (S Spain) runs parallel to the coast and very close to it, between the towns of Adra and Motril. In this area, with very complicated topography, the slopes of the natural hillsides are very steep so the highway is characterized by large excavations on the mountain side (north). We analysed a failure occurred in 11 March 2021 in a high cut-slope located in the Km 354.3 of the A-7 highway. In this specific area, there are grey phyllites with an schistosity that generally dips gently towards the southwest. The phyllites belong to a unit of quartzites, quartzitic phyllites, and phyllites, along with calc-schists, with local presence of gypsum, which is attributed to a Permian-Triassic age. Phyllites are in direct mechanical contact with quartzitic phyllites and quartzites. Orientation, both of the schistosity planes and the contact between the two lithologies, combined with the alignment of the highway in this area (NW-SE), is clearly unfavourable from the perspective of slope stability. A Schmidt hammer campaing allowed us to observe that the strength parameters of the phyllites are significantly lower than those of the quartzitic phyllites layers. Moreover, in the boundary between quartzite and phyllite rocks, multiple brittle deformation zones can be recognized, which means the friction angle along these surfaces could be close to the residual angle. This factor, along with the unfavourable orientation of the schistosity in the phyllites, could have been one of the main determining causes to the instability that affected the A7 highway at this location.

To reduce dilution is the main objective in mining operations. For this case, it is necessary to improve the mine operations and define geotechnical parameters. To reduce dilution, the face drilling and charging standards should be improved as much as possible. Damage zone for the rock mass is another parameter to consider reducing dilution. Improvements began to reduce dilution regarding these issues at Tuprag Efemçukuru Gold Mine where the mining methods are long hole open stope, blind up hole and drift and fill. Initially, string loading was applied on face contour drills and the quality of parallel drillings was improved. In addition to operational applications, geotechnical parameters were correlated with overbreak. The cores for all infill drills have been logged with Barton Q system for geotechnical assessments at Tuprag Efemçukuru Gold Mine. Geotechnical core logging provides useful information to reveal damage zone. According to Q values of drifts, the face contour drillings have been relocated to inside the design for definition of damage zone. The overbreak results have been correlated with Q values section by section to create a legend to locate of the face contour drillings on the design. Q values, overbreak length, relocation distance of the face contour drillings on the design and drill hole diameter parameters were considered to calculate damage zone length for the back and the walls. Due to calculation, spots of each result have been put on damage zone length – Q values graphics for the back and the walls. Distribution of spots created a range on the graphics of the back and the walls. Maximum and minimum limits of the range for the back and the walls were drawn and emerged their formulas on the graphics. Consequently, created legend to relocation inside the design of the face contour drillings was revised with the formulas. A block model, based on the legend, was created as a guide for recommendation to operations. Stopes which have similar rock mass quality were compared as after and before applications to knowledge of benefits. The results showed dilution to reduce for ore drifts between 4% and 15% and for waste drifts between 6% and 11%. Besides, it supplied yield for diesel consumption, consumable consumption, and duration of operation cycle

The weathering process significantly affects the mineralogical and geochemical characteristics of rocks that finally alters the engineering properties of rocks. Three different weathering grades (fresh, slightly, and moderately weathered) of gneiss were collected from Kullu, Himachal Pradesh, India. A comprehensive qualitative and quantitative description is used to point out the weathering grades of gneissic rock. The mineralogical alterations were determined using thin-section analysis. The petrographic analysis revealed that a major alteration was observed in plagioclase feldspar. The sericitization of plagioclase is mainly noticed with progressive weathering. The quartz grains remain intact and unaltered in fresh and slightly weathered stages while minor fracturing was observed in the moderately weathered stage. The partial transformation of biotite was also observed in moderately weathered gneiss. The chemical composition of these three weathering grades of gneiss was determined using X-ray fluorescence (XRF) analysis. The Plagioclase Index of Alteration (PIA) shows a significant increase with increasing weathering grades that supports the higher alteration of plagioclase during the weathering of gneissic rock of Himachal Pradesh, India.

Rock bolting, rock reinforcement is an ongoing work. Its a necessity in all rock excavation related application areas i.e. in civil infrastrcuture projects, underground mining, open pit mining, tunneling etc. The subject of rock reinforcement, rock bolting is contineoulsy evolving and there has been a lot of new developments has happened over the years e.g. new types of rock bolts, development of rock bolting-reinforcement machines, design methdologies, application process etc. This paper will be specifically focusing on open rock slopes above ground. We have observed an application and methodological process error for applying rock reinforcement, rock bolting on an open rock slopes above ground. The problem is our current practice of installing rock bolts or rock reinforcement on rock slopes above ground is either based on random observation or systematic empirical design formula. In author's view, most of the time existing way of installing rock bolts, rock reinformcement miss to consider the impact of structural geology, geometry, gravational slip surface of rock blocks. In this paper we are presenting a new approach called 'cross-bedding-cross-bolting (CBRB)' for open rock slopes above ground. This new approach and application methodology for open rock slopes above ground mainly consider structural geology, geometry and gravational slip surface of rock blocks. We will present the conceptual theroy as well as the applicaiton methodology of the 'cross-bedding-cross-bolting (CBRB)' approach. The paper will also brifely review and present the existing practices for rock bolting, rock reinforcement, standards followed and application methodology. Our expected out come from this paper is to present a safe and cost efective method for securing open rock slopes above ground. Also, to provide a new approach and corrective measures for application of rock bolt, rock reinforcement for open rock slopes above ground.

Mine tunnels are constructed to offer access for various purposes. The tunnel excavation's primary purpose in this specific mine was to provide ventilation and access to the second-ary orebody. The Malmani dolomites, which contain most natural water resources, directly overlie the Black Reef formation, which is composed of extremely fine to silt quartzite in-terbedded with silt carbonaceous shale. Unexpected ground conditions caused significant delays during the tunnel construction (e.g., fault zone, dykes, laminated carbonaceous shales). After the inception of the fault zone, the tunnel construction could only advance for 9 m. The tunnel construction halted due to the porous ground conditions of the carbo-naceous shale that could not be supported. The layered carbonaceous rock mass presented difficulties due to its geochemical degradation. A suitable feasibility geotechnical program would have aided in the viability of excavating this tunnel within the Malmani dolomites and the possible risk of mining into the water compartments

Rock mass classifications have gained great importance for the last decades for tunneling engineering. Apart from some previous attempts along the XX century, the start of the rock mass classifications can be stated during the 70s with the development of the Rock Mass Rating (RMR) and the Q index, which are regarded at present as the references for most of the technicians, engineers and geologists. More recently, other classifications have been proposed, like the Geological Strength Index (GSI) and the Rock Mass Index (RMi), which are attracting more interest. Unlike in other fields, authors of those rock mass classifications suggested employing more than one system with the aim of capturing different aspects of the rock mass as each of them considers different factors for calculating the value. Therefore, some correlations have been proposed between two of the classifications for obtaining the rate in other system when having one of them. This paper aims to advance in this field and observe if it is feasible to correlate these four rock mass classifications: RMR, Q index, GSI, and RMi. With this aim, the data obtained from the Seberetxe tunnel, with approximately 600 m, in the new segment of the Southern Metropolitan By-Pass of Bilbao, in Spain, was employed. This twin tunnel was excavated by drill and blast in siltstone. Results indicate that the four systems can be correlated with acceptable accuracy in a homogeneous rock type with different weathering. This study shows that correlations can be developed between two of the four rock mass classifications as long as the same rock type is analyzed.

The rock mass is composed of homogeneous and heterogeneous rocks, where the stresses are transmitted with their specific values by: condition, depth and properties of the rocks; each stress has three components with their respective direction and their respective magnitude, being the major principal stress σ1, and the minor principal stresses σ3 and σ2. In the rock massif, stresses are recognized by their influence on underground excavations and must be measured. To measure in situ stresses, the Drillhole Detonation Method (DDM) is proposed, which detects stresses in two processes. 1) Detonation of a drillhole obtaining radial cracks of different length and direction, by joining the ends of the cracks elliptical figures are formed called ellipse of stresses whit their major and minor axes. 2) To evaluate the magnitude of the major stress we use the formula σ1 = FC1 · γ · Z, to evaluate the magnitude of the minor stress we use the formula σ3 = FC3 · k · γ · Z. The Correction Factor (CF) = 0.0056 (measured angle) + 1.003 and the coefficient k is obtained by dividing the length of the horizontal axes by the vertical axes of the ellipse. To obtain the direction and magnitude of σ2 a drilhole is detonated in the direction perpendicular to what has been done to obtain σ1 and σ3. The major axis of the stress ellipse represents σ1. The measurement of stresses by the Drillhole Detonation Method (DDM) is: low cost, calculated at the same time, contributes to optimize the support of underground excavations.

The term discontinuity covers a series of geological structures, very different both in origin and mechanical behavior. It includes the formational planes, like bedding planes and foliation planes, moving fractures and the joints. In order to perform more realistic geomechanical classification and modeling, for the geomechanical rock mass classifications, the term discontinuity should allow to differentiate between the formational structural planes, not related to the stress state, and the joints, that actually depend on the regionally and local stresses. Another inconsistency arises when evaluating roughness, since joints cannot present polished planes, which can apply to moving fractures, in general with different mechanical behaviors from each other. The same is true when applying the term persistence to a formational plane, whose extension is infinite when compared to a recent fracture or a joint. According to recent research results of stability analysis in tunnels and rock slopes, related to the new application criteria for joint formation based on changes in confining forces, this paper proposes the need for a new approach in the application of terminology for the rock mass geomechanical classification and for the geotechnical characterization, eliminating the inconsistencies that arise when applying some definitions indiscriminately to any structure and origin of the plane.

The slope stability analysis, the critical height, the estimation of force on retaining walls or the calculation of the anchor force, requires a mathematical formulation that goes through an optimization process to determine the critical sliding surface. The process consists of the solution of a derivative with respect to the critical surface. The analytical solutions that have been found are based on a simple geometry for a triangular shaped sliding body. In this paper a solution procedure is proposed for cases of any geometry, including complex geometries. A simple numerical method called incremental method, is developed, specially designed for the analysis of stability, thrust or anchorage design by means of a spread-sheet. The methodology allows static or pseudo-static analysis. Several analysis cases are shown and their solution is compared with the results using advanced numerical methods, where an excellent correspondence is demonstrated.

In this investigation, two different cooling techniques (i.e. water- and air-cooling methods) has been used in order to study the influence of different heating-cooling treatments on the physical properties, microstructural characteristics and point load strength of Himalayan granite collect-ed from Sangla valley, Himachal Pradesh. The temperatures for heat treatment were targeted at 100, 300, 400, 500 and 600°C. As a response to thermal treatments, increase in effective po-rosity and increase in damage coefficient occurs which causes exponential decrease in point load strength. It decreases ~74% and ~81% under air-cooling and water cooling respectively after heating of about 600oC with reference to thermally untreated specimens. The microstruc-tural study reveals that the increase in crack density due to thermal treatments induce intra-, in-ter- and trans-granular cracks, at and beyond 300oC onwards and their coalescence with each other at higher temperatures (i.e. ≥ 500oC) under both the thermal treatments contribute to-wards the variation in point load strength of thermally treated granites.

This study investigates the influence of flaw inclination angles on the mechanical response of rock-like specimens with pre-existing flaws under dynamic loading conditions, employing the Discrete Element Method (DEM) software UDEC. Several Split Hopkinson Pressure Bar (SHPB) compression tests were previously conducted on these specimens, each containing a single non-persistent flaw. The study considered two flaw orientations and a single flaw. Earlier experimental investigations revealed that specimens with unfilled flaws exhibited the highest dependency on flaw inclination angle. Notably, the weakest mechanical response for flawed specimens was observed at a 30° flaw orientation, aligning with the shear failure plane of intact specimens. UDEC numerical simulations were performed to further elucidate the experimental findings. The peak stress response of flaw models obtained were less than intact rock models, which matched well with the experimental results. These simulations provided invaluable insights into the dynamic behaviour of rock-like specimens. .

This study addresses the challenge of accurately estimating support forces to mitigate rock slope failures, employing inverse reliability methods like the Performance Measure Approach (PMA) and the Probabilistic Sufficiency Factor (PSF). A comparison with conventional for-ward reliability approaches, such as the Reliability Index Approach (RIA) and the Forward Monte-Carlo Approach (FMC), highlights the advantages of inverse reliability methods. Focusing on wedge-shaped failure scenarios in the Himalayas, the research emphasizes the applicability and effectiveness of the PMA and the PSF. Results indicate that these inverse methods offer improved accuracy and computational efficiency compared to traditional approaches, making them valuable tools for support force estimation in rock slope engineering. Their reduced computational effort enhances practical applicability, positioning them as promising alternatives in the field.

For coal extraction and removal of overburden, blasting is commonly used in most open-pit coal mines. Blasting generates shock energy that crushes the rock initially and then propagates in the form of waves through the surrounding rock. These ground vibrations are detrimental to the safety of the structures that are located in the vicinity. Though the interaction between blast waves and different structures has been extensively studied to safeguard these structures, the specific behaviour of brick masonry structures under blast-induced ground vibrations (BIGV) remains largely unexplored. The influence of BIGV on structural safety necessitates the incorporation of dynamic structural characteristics into safety guidelines to ensure the safeguarding of these structures. In order to investigate the actual behaviour of structures located near the periphery of a mine, a brick masonry wall was modeled in ABAQUS and analysed under the influence of 10 ground vibration time histories from distinct blast events with varying PPV (Peak Particle Velocity) values. A simplified micro modeling approach utilizing the CDP (Concrete Damage Plasticity) model was employed to accurately predict the wall's response. A comparative analysis was conducted, revealing contrary to popular beliefs, that even at very low PPV values, the structure exhibited significant deformations and stresses. Conversely, in some instances with very high PPV values, the structure remained safe. The primary finding underscores that using PPV alone as the determinant of structural safety possesses several limitations. It is imperative to consider the dynamic characteristics of structures in blast designs for a more comprehensive assessment of safety.

Thermal properties describe how heat and temperature behave in a rock. Sandstone is a very common sedimentary rock found in layers formation in coal mining areas. This rock is used for underground backfilling purposes and other applications in mining. For optimizing the heat load in underground mines, the thermal properties of sedimentary rock are very important. We analyze the results of measurements of the thermal properties, porosity and density of sandstone rocks from the Godavari coal basin, Telangana. The thermal properties were measured by the “FOX50” instrument at room temperature (25⁰C). The thermal conductivity of sandstone rocks ranges from 0.65 to 4.38 W/m. K and it is strongly depending on porosity and density. The average range of density of rock samples is 2.28 to 2.50 g/cm³ and average porosity ranges from 6 to 13 %. The results indicate variations in thermal conductivity and diffusivity across different locations, while specific heat appears consistent throughout all regions. The study also investigated how density and porosity affect the thermal properties of rocks. It was found that thermal conductivity increases with density and decreases with porosity. The assessment of thermal conductivity from porosity and density is made possible by the equations that are provided.

Investigating the possible correlation between various measures of rock strength is a common practice in experimental rock mechanics, as the results of relatively simple and economical tests can yield estimates of mechanical properties that would require more sophisticated experimental procedures. For example, the Schmidt hammer test is one of these experimental setups that have been used to indirectly determine the uniaxial compressive strength and the static modulus of elasticity. Nevertheless, this experimental setup has not been extensively used for the indirect determination of other important mechanical properties, such as the point load strength index and the indirect tensile strength obtained from the Brazilian strength test. For this reason, an experimental program was carried out involving at first the direct determination of the Schmidt hardness, the point load strength index, and the Brazilian tensile strength for rock types of various origins outcropped at the southern part of the Attica Peninsula, Greece. Subsequently, the statistical processing of these results was performed via simple regression techniques, while very good relations were established in the form of exponential equations between the Schmidt hardness and both the point load strength index and the Brazilian tensile strength. Our results can be used for preliminary investigations, at least in the study region, and can enrich our knowledge regarding the correlation between the mechanical properties under consideration.

Traditionally employed laboratory tests allow obtaining strength and deformation properties of rocks, such as the uniaxial compressive strength, tensile strength and Young's modulus. Andesite, a pivotal rock in Ecuador, holds significant relevance to civil engineering and mining, yet its geomechanical properties remain inadequately explored. This study delves into the physical, petrographic, and geomechanical characteristics of andesite from the Tungurahua volcanics geological unit in the Real Cordillera of the Ecuadorian Andes. The findings reveal a massive andesite with porphyritic and hyalopilitic textures, boasting high density (2690±36 kg/m³), low porosity (2.11±1.32%), and minimal water absorption (0.31±0.13%). Mechanically, it proves to be a high-strength rock (204 MPa) with nonlinear elastic behavior up to 40% of the maximum strength and an average secant Young's modulus of 35.06±2.47 GPa. These results contribute to enhance our understanding of Andean andesite properties from the Tungurahua volcanics geological unit.

Limit States Design (LSD), which represents an implementation of Reliability Based Design (RBD), is becoming more widely used in geotechnical engineering. Fundamentally this requires a probabilistic characterization of all uncertainties in a given geotechnical engineering problem. Uncertainty is inherent to rock mechanics and rock engineering, and generally stems from factors such as complex geology, vagueness in instability mechanisms and the highly nonlinear mechanical behaviour of rock masses. Such uncertainties are commonly considered using subjective qualitative assessments, SQAs, using what are known as linguistic variables, e.g. a rock mass may be described as being “slightly weathered”. In this paper we demonstrate why SQAs must be considered as ordinal and not metric (i.e. measured) values. We thus show both why it is not possible to directly consider SQAs in a probabilistic setting, and how doing so may lead to significant errors. To overcome this severe limitation of SQAs we apply techniques recently developed in the broader field of imprecise probabilities in engineering analyses. In particular, we examine how SQAs may advantageously be firstly converted into fuzzy numbers and from those into probabilistic variables. An immediate benefit of this approach is that conditional probability can be used to examine situations where both quantitative measurements (e.g. intact rock strength) and SQAs exist. We demonstrate this by constructing a Bayesian network that combines the two characteristics of intact rock strength and degree of weathering, and show how this leads to an interpretation of rock mass condition that directly supports LSD. Using an example from the literature, we conclude with a brief discussion of how such Bayesian networks can be applied to complex rock engineering projects.

This study assesses the influence of petrophysical properties, petrographic features, and depth on capillary imbibition of basalts and lapillistones from the Upper and Middle Vol-canic Complexes of Madeira Island, Portugal, via multivariate statistical analyses and ma-chine learning methods approach. Results demonstrated that the combined effect of mesofabric, porosity, and pore-type connectedness controls capillary imbibition in lapillis-tones and revealed that there is a strong direct relationship between porosity degree and water absorption coefficient by capillarity, C, in all basalts. The tendency for spontaneous imbibition to decrease with increasing depth is as expected in the studied basalts, except for the sections 23.70 27.20 m and 31.5 34.8 m in two different samples where evidence of fracturing episodes was found which leads to a dual-porosity system that favours water absorption. C is proposed as a complementary coefficient in geotechnical studies of vol-canic rocks.

Pore microstructure in rocks regards shape, volume concentration, distribution and connectivity of pores and cracks and has a substantial influence on many macroscopically observed properties such as rock strength and its deformation and fracture behaviour. Cracks in rocks initiate and propagate in response to the applied stress, with the crack path often driven by local distribution of micro-flaws such as cavities, inclusions, fossils, grain boundaries, mineral cleavage planes, and micro-cracks inside the rock. For sedimentary rocks like sandstone, mineralogical composition of interstitial materials between framework grains is also important factor influencing crack parameters. Although these phenomena are generally known and widely described in the macroscale or mesoscale, the microscopic aspects have not been studied very extensively yet. In order to better understand the process which leads from micro-cracks to macroscopic fracturing and thus extends in scale from millimetres to kilometres, the crack initiation, propagation and growth should be studied just in the microscale. In practical terms, knowledge of the failure behaviour of rock mass due to crack propagation is much needed in some important engineering cases, such as, CO₂ sequestration, high-level radioactive waste disposal or stability of underground workings and slopes. In this contribution, the basic outputs of the study of influence of rock microstructure and composition on the fracture toughness of rocks measured by the chevron notch technique and subsequent analysis of cracks geometry using the X-ray computed tomography are presented. Rock samples selected for experiments are representatives of all three major groups of rocks (igneous, sedimentary and metamorphic), from which sediments, namely sandstones, are the most numerous. Four basic crack parameters were investigated on all rock specimens: (1) crack length, (2) crack width, (3) angle of crack deflection from crack initiation zone, and (4) description of crack course. On the basis of laboratory experiments and analyses, the following fundamental conclusions can be made: (1) the value of crack length generally increases with decreasing rock porosity and this trend is most pronounced within the sandstones, (2) the value of crack length generally increases with increasing value of fracture toughness, (3) the value of the crack length of the sandstones increases with a growing degree of silicification of the matrix, (4) in sandstones, the cracks propagation goes preferably throughout the pore space and may be influenced by limonite pigment and (5) in low-porosity crystalline igneous and metamorphic rocks, the cracks spread along the grain boundaries and often also break grains.

Erosion can cause irreparable damage when it occurs on elaborated elements of the cultural heritage. Even very small erosion rates can result in the loss of valuable sculptural details. Rock erodibility is defined as the lithology-based susceptibility to erosion for a given set of environmental conditions. Wind, rain and hail are examples of the main erosion agents affecting the building rocks used in architectural heritage. Human activity can also be the cause of severe erosion processes in rocks. However, the rock suscebility to erosion determines the efficacy of the erosive process and the effective final material loss from the stone surface. Several research lines address the study of rock erodibility in different contexts (fluvial geomorphology, generation of sediments, tunnel construction, etc.) offering a quantitative approach using indices. However, there are very few works focused on the erodibility of rocks in the heritage context. Erosion, weathering and durability are closely related concepts, usually considered synonymous, but they require an individualized study since the effects and causes associated with each process are very different. In this work, a first approach is proposed to the study of the susceptibility to the erosion of four building rocks widely used in the cultural heritage of Spain. Selected rocks are porous limestones and sandstones with porosity higher than 10%. These rock types are frequent in architectural heritage due to both their availability and their high workability. Erosion Susceptibility of studied rocks has been analysed taking into account both petrographic (texture, structure, mineralogy, heterogeneity and anisotropy) and petrophysical (porosity, pore size distribution and mechanical properties) aspects. The resistance to erosion has been determined by means of the laboratory wide wheel abrasion test. Results show that erosion susceptibility is directly correlated with porosity and inversely with mechanical properties. Grain cohesion, friction angle and tensile strength are key parameters to determine erodibility. Mineralogy probably modify the susceptibility to the material loss, being more resistant the quartz-based rocks than the limestones. Future works, however, should verify the results obtained in this approach including new data and new rock types.

This work presents a multiproxy methodology that combines both in-situ outcrop tests and la-boratory methods, for the petrophysical characterization of a potential sandstone CO2 reservoir. Multiproxy methodology was designed to obtain a complete petrophysical and geomechanical characterization including non-conventional techniques in this type of study. Considered sandstone reservoir corresponds to a detrital Buntsandstein facies of the Iberia Chain (central Spain). Specifically, the involved formations are Aranda-Carcalejos (possible reservoir) and Rané (seal). Four main facies were recognized in the stratigraphic sequence, and the petrophysical analysis of each one was carried out. Main petrophysical differences are found between both channel and sheetflood facies, the former being much more porous and permea-ble and less mechanically resistant than the sheetflood facies. The comparative analysis also highlights the strengths and weaknesses of this multiproxy methodology. This work is part of the in-deep geological characterization of a geological complex for CO2 storage potential evaluation.