Slate Samples Research Articles

Juvenile source nature of the North Tianshan turbidites and its tectonic implication

Abstract Sediments within accretionary complexes, preserving key information on crust growth history of Central Asian Orogenic Belt, did not get enough attention previously. Here, we conduct comprehensive geochemical study on the turbidites from the North Tianshan Accretionary Complex (NTAC) in the Chinese West Tianshan orogen, which is a good example of sediments derived from juvenile materials. The turbidites, composed of sandstone, siltstone, and argillaceous siliceous rocks, are mainly Carboniferous. All the investigated samples have relatively low Chemical Index of Alteration values (35–63) and Plagioclase Index of Alteration values (34–68), indicating relatively weak weathering before erosion and deposition. The sandstone and siltstone, and slate samples display high Index of Compositional Variability values of 0.89–1.50 and 0.89–0.93, suggesting a relatively immature source. The sandstones and siltstones were mainly derived from intermediate igneous rocks, and the slates from felsic igneous rocks, formed in oceanic/continental arc settings. The investigated samples roughly display high positive εNd(t) values (mainly at +5.5 to +7.9, except one spot at +0.8), with corresponding Nd model ages at 672 Ma–522 Ma (except one at ∼1.1 Ga). Combined with the previous studies, we suggest that the turbidites in the NTAC were mainly derived from intermediate to felsic igneous rocks with juvenile arc signature, and thus the northern Chinese West Tianshan is a typical site with significant Phanerozoic crust growth.

Stability Analysis of Strongly Weathered Muddy Slate Slopes Considering Softening Conditions of Water Immersion

To understand the stability of strongly weathered muddy slate slopes under water immersion effects, we obtained shear strength parameters of the weakly layered structures within this slate through direct shear tests. Point load tests were performed on in-site slate samples with varying water immersion durations to assess the water immersion’s softening impact on slate strength. Results highlight that muddy slate strength presents pronounced random variability, declining as water immersion duration increases. Drawing from shear strength parameters and the water immersion softening observed in laboratory and in-site tests, we formulated a numerical slope model that considers layered structures and water immersion conditions to evaluate slope stability. Numerical simulations suggest that the slate slope’s sliding surface, when layered, does not consistently form a basic circular arc or straight line. The slope safety factor (FOS) drops below 3, marking a notable decrease compared to a homogeneous slope (FOS = 3.22). In the model, multiple secondary sliding surfaces can emerge, leading to a sliding band with a specific thickness after introducing the random distribution of layer strength parameters. This further reduces the slope’s FOS to below 2.9. Water immersion makes slopes inclined to slide following the layered structure. If the dip angle of the slate’s layered structure is less steep than the slope’s dip angle, water immersion notably diminishes the FOS, which can dip to a minimum of 1.12.

Anisotropic shearing mechanism of Kangding slate: Experimental investigation and numerical analysis

The shear mechanical behavior is regarded as an essential factor affecting the stability of the surrounding rocks in underground engineering. The shear strength and failure mechanisms of layered rock are significantly affected by the foliation angles. Direct shear tests were conducted on cubic slate samples with foliation angles of 0°, 30°, 45°, 60°, and 90°. The effect of foliation angles on failure patterns, acoustic emission (AE) characteristics, and shear strength parameters was analyzed. Based on AE characteristics, the slate failure process could be divided into four stages: quiet period, step-like increasing period, dramatic increasing period, and remission period. A new empirical expression of cohesion for layered rock was proposed, which was compared with linear and sinusoidal cohesion expressions based on the results made by this paper and previous experiments. The comparative analysis demonstrated that the new expression has better prediction ability than other expressions. The proposed empirical equation was used for direct shear simulations with the combined finite-discrete element method (FDEM), and it was found to align well with the experimental results. Considering both computational efficiency and accuracy, it was recommended to use a shear rate of 0.01 m/s for FDEM to carry out direct shear simulations. To balance the relationship between the number of elements and the simulation results in the direct shear simulations, the recommended element size is 1 mm.

An Experimental Investigation on the Foliation Strike-Angle Effect of Layered Hard Rock under Engineering Triaxial Stress Path.

Deep underground engineering encounters substantial layered hard rock formations, and the engineering triaxial stress path involves an increase in maximum principal stress, constant intermediate principal stress, and a decrease in minimum principal stress. However, previous research has focused on rock layer angles under conventional triaxial stress conditions, disregarding the influence of foliation strike angles in engineering triaxial stress scenarios. This study experimentally investigates the effects of foliation strike angles on layered hard rock under an engineering triaxial stress path. To account for the brittleness of layered hard rock, we propose a specific small sample-processing method tailored to the foliation strike angle. True triaxial loading tests are conducted on steep, thin slate samples with two different loading orientations, accompanied by acoustic emission monitoring. Results indicate that the strength under a traditional true triaxial compression condition is similar for specimens with 90° and 0° strike angles. Stress-strain curves show that larger deformations occur perpendicular to bedding planes, while surface fractures propagate exclusively along the bedding planes. Mechanical responses differ significantly between specimens subjected to the engineering triaxial stress path at 0° and 90° strike angles compared to conventional true triaxial loading tests, with a lower bearing capacity and differentiated intermediate and minimum principal strains in the 0° case. Conversely, the 90° case exhibits a higher bearing capacity, consistent deformation, and more acoustic emission events. Numerical simulations comparing plastic zone sizes during actual underground excavation support these conclusions. These findings highlight the effects of foliation strike angles, favoring the 90° strike-angle configuration for excavation activities and providing enhanced stability in the surrounding rock mass.

A novel pulse-decay-balance method for smooth rock joint aperture measurement

A novel pulse-decay-balance (PDB) method was proposed to simultaneously measure hydraulic and mechanical apertures (e and E) under stress. The YOKO2 system was modified into a closed system to measure the e and E of saw-cut and foliated slate samples under a confining (normal) stress of up to 60 MPa. The hydraulic aperture was determined based on analysis of the pressure decay curve, and the mechanical aperture was determined based on the joint volume measurement (JV method) by determining the balance pressure. The hydraulic aperture estimated using the proposed method was comparable to that measured in steady-state tests. The hydraulic apertures of the saw-cut and foliated slate samples estimated using the simplified and general analytical solutions were in good agreement, especially for smooth joints under high normal stress. However, the error in the hydraulic aperture estimation, induced by neglecting the specific storage of the rock joint, is non-negligible for rough rock joints under low normal stress. A regression function based on the stress-dependent E and e fitted well with the experimental data to describe the E-e relationship. Our testing results, which show a decreasing trend in the E/e ratio with decreasing e, contradict the existing (E/e)-e relation, at least for smooth joints. The measurable e via the closed YOKO2 system was several tens of microns. Although the measurable E is below 1 μm, the best measurement range of E is roughly 1000 to 100,000 μm. A standard sample size for the conventional triaxial test was suggested to harmonize the optimum measurement ranges of the hydraulic and mechanical apertures. In this case, an analytical solution for the pulsed decay that considers the specific storage of the rock joint should be used to reduce the error in estimating hydraulic apertures.

Quantitative investigation on localized deformation process of rocks by uniaxial test and digital image correlation

Determining the localized deformation mechanism is of vital importance to understand the failure processes of geomaterials in practical engineering. In this study, uniaxial monotonic and cyclic loading tests of slate samples were conducted and the failure processes were recorded by using the AE system and digital image correlation (DIC). The results show that the deformation field variance increases significantly in the initiation of the macro-scale failure stage. Under cyclic loading, the shape of the stress-variance hysteresis curve varies with increasing upper limit stress, and four types of stress-variance hysteresis curves were revealed. Increasing lag time of variance indicates gradual accumulation of damage to the sample. The comprehensive analysis of the evolution process of damage variables defined by cumulative AE counts and variance reveals that the rock failure process can be divided into crack closure stage, initial damage stage, stable development stage, accelerated development stage and failure stage. By proposing the differentiation rate, it is found that there are apparent failure precursor points under monotonic and cyclic loading.

Experimental investigation into rock burst proneness of rock materials considering strain rate and size effect

In deep rock engineering, evaluating the likelihood of rock burst is imperative to ensure safety. This study proposes a new metric, the post-peak dissipated energy index, which accounts for strain rate and size effects in assessment of the rock burst proneness of a rock mass. To investigate rock burst proneness, conventional compression tests were conducted on limestone and slate samples with different length to diameter (L/D) ratios (ranging from 0.3 to 1.5) at four different strain rates (0.005, 0.01, 0.5, and 1.0 s−1). Based on the testing observations, the actual rock burst proneness was classified into three categories (no risk, low risk, and high risk). A new criterion was also established using the post-peak dissipated energy index, which is the ratio of elastic energy to total dissipated energy. The impact of the strain rate and L/D ratio on rock burst proneness was analyzed. The results indicated that increased strain rates cause a strong hardening effect, leading to staged growth of rock burst proneness. However, the rock burst proneness decreases non-linearly with the increasing L/D ratio. The accuracy of the proposed criterion was validated by comparison with existing criteria, demonstrating that the energy-based index ensures a reliable evaluation of the rock burst proneness of a rock mass. The proposed method has excellent potential for practical application in deep rock engineering.

Fire resistance of roofing slates: Mechanical, mineralogical and aesthetic changes alongside temperature increase

Fire is a major destructive agent for dimension stone. Practically all historic buildings have suffered one or more fires over the course of their lifespan. There are numerous studies on the effect of fire on stone. Generally speaking, these effects can be divided into aesthetic and structural. Aesthetic effects involve a color shift to reddish hues, due to the oxidation processes triggered by temperature increase. Moreover, structural effects involve the formation of cracks and delaminations that may cause the rock to disintegrate. However, even though roofing slates are a group of metamorphic rocks that are widely represented in the historical architectural heritage of many European countries, none of the scientific studies alluded to above have taken them into account. The present study examines 6 lithotypes, covering the metamorphic range of rocks used as roofing slates. The roofing slates were subjected to a heating test reaching 900 °C, and then analyzed using X-ray diffraction and fluorescence, Thermogravimetric and Differential Thermal analyses, and were also tested for bending strength and water absorption following the European standard for roofing slates, EN 12326. All samples studied exhibited a reduction in their bending strength, together with an increase in water absorption. Likewise, the oxidation processes triggered by the high temperatures induced a general oxidation of the iron, lending all of the samples a reddish hue. On the other hand, the roofing slate samples proved to be non-combustible and did not release any toxic or hazardous fumes.

Anisotropy and Directivity Effects on Uniaxial Compression of Carbonaceous Slate Form Jinman Mine

To determine the anisotropic mechanical characteristics of carbonaceous slate at the Jinman Mine located in Lancang River Gorge, China, uniaxial compression, acoustic emission (AE) monitoring, and scanning electron microscopy (SEM) tests were conducted. The results show that stress loading directions and bedding effects have a significant impact on strain characteristics. The deformation of slate undergoes compaction, elastic, damage accumulation, and failure stages, and there are significant differences in strain paths. The mechanical properties of grey and carbonaceous slate have significant features, and variations of these properties of carbonaceous slate are more than that of grey slate. The discrete degree is significantly related to the direction of stress loading and different types of slate structures. The AE response intensity is related to the loading mode and slate type. A sudden increase in the AE cumulative ring number near peak stress indicates instability and rupture and is a precursor of rock rupture. The failure patterns and fracture characteristics are significantly correlated to the layered structure of the slate. Slates subjected to vertical loading and parallel loading conditions are dominated by shear fracture and tensile fracture, respectively. The peak strains of gray and carbonaceous slate correspond to brittle failure. The SEM tests indicate that slate samples subjected to parallel loading primarily show a tensile failure compared with slate samples subjected to vertical loading, with fractured sections being of lesser roughness, and scattered fractures and sections being smooth without obvious protrusions or cracks.

Fracture Transmissivity in Prospective Host Rocks for Enhanced Geothermal Systems (EGS)

We experimentally determined the hydraulic properties of fractures within various rock types, focusing on a variety of Variscan rocks. Flow-through experiments were performed on slate, graywacke, quartzite, granite, natural fault gouge, and claystone samples containing an artificial fracture with a given roughness. For slate samples, the hydraulic transmissivity of the fractures was measured at confining pressures, pc, at up to 50 MPa, temperatures, T, between 25 and 100 °C, and differential stress, σ, acting perpendicular to the fracture surface of up to 45 MPa. Fracture transmissivity decreases non-linearly and irreversibly by about an order of magnitude with increasing confining pressure and differential stress, with a slightly stronger influence of pc than of σ. Increasing temperature reduces fracture transmissivity only at high confining pressures when the fracture aperture is already low. An increase in the fracture surface roughness by about three times yields an initial fracture transmissivity of almost one order of magnitude higher. Fractures with similar surface roughness display the highest initial transmissivity within slate, graywacke, quartzite and granite samples, whereas the transmissivity in claystone and granitic gouge material is up to several orders of magnitude lower. The reduction in transmissivity with increasing stress at room temperature varies with composition and uniaxial strength, where the deduction is lowest for rocks with a high fraction of strong minerals and associated high brittleness and strength. Microstructural investigations suggest that the reduction is induced by the compaction of the matrix and crushing of strong asperities. Our results suggest that for a given surface roughness, the fracture transmissivity of slate as an example of a target reservoir for unconventional EGS, is comparable to that of other hard rocks, e.g., granite, whereas highly altered and/or clay-bearing rocks display poor potential for extracting geothermal energy from discrete fractures.

Assessment of pozzolanic material for manufacturing of Portland Pozzolana cement (PPC) by the comparison of Ordinary Portland cement (OPC)

In the present study physicochemical characterization of slate sample was carried out which was collected from slate mine in Lasbela District, Baluchistan. Slate was evaluated for its effectiveness as partial replacement of ordinary Portland cement (OPC) in the production of Portland Pozzolana cement (PPC). The grain size analysis of crushed slate sample using ball mill revealed that maximum fraction retained on 44 μm was about 72.8 %. Sum of the major oxides (SiO2 + Al2O3 + Fe2O3) is about 90.09 % that meet the requirement as per ASTM C 618 (minimum 70.0 %). Other oxides including SO3 (<0.05), CaO (4.04), MgO (1.66), K2O (0.10), Na2O (0.16), TiO2 (0.35), MnO (<0.02) and Cl (0.12) also meet the international standard of ASTM C 618 for PPC. OPC without and with using slate sample in a ratio of 5 % and 10 % with clinker was tested to measure compressive strength, physical tests and setting time. The results showed that after 5 % and 10 % replacement, insignificant effect was observed on the physical properties, setting time and compressive strength in 2-, 7- and 28-days curing. Hence, slate can be used as natural pozzolan for manufacturing PPC. It is cost effective for the production of cement as well as to sustain the resources of limestone for long time and reducing emission of CO2 in the environment. It can also be used in the sulfate rich environment, coastal areas especially for the construction of dams and bridges.

Hydrothermal Extraction of Amorphous Silica from Locally Available Slate

Slate is a naturally available aluminous silicate based material and can be used as a good source for silica extraction. In the current investigation, the slate sample was passed through calcination and acid leaching processes to decrease alumina contents and other major constituents. Silica extraction was performed by alkaline hydrothermal treatment of a given slate sample followed by acidic precipitation. Different steps, including the effect of concentration of sodium hydroxide solution, reaction time, the ratio of the mass of sample to volume of alkaline solution, the temperature of dispersion, and pH of the filtrate, were investigated to extract the maximum amount of pure amorphous silica. The extracted silica was physicochemically analyzed through XRF, XRD, FT-IR spectroscopy, and SEM techniques. The amorphous nature of the extracted silica is evident from XRD and SEM studies, while FT-IR studies support its purity, showing peaks of only Si–O–Si bonds. The purity of the extracted silica was further confirmed via XRF spectroscopic analysis and a hydrofluoric acid test.

A Comparison of Mechanical Properties and Failure Processes of Saturated and Unsaturated Slate from Sichuan-Tibet Plateau Area, China

Abstract Water content significantly affects the physical and mechanical properties of rock and can cause rock mass to become unstable. This, in turn, can cause geologic disasters such as water inrush and surrounding rock deformation. Uniaxial compression experiments on slate samples drilled from the surrounding rock of a tunnel in the Chinese Sichuan-Tibet Plateau area were performed coupled with acoustic emission (AE) monitoring. The changes in mechanical properties and failure processes of unsaturated and saturated slates were investigated comparatively through test results. Phenomena of a slight drop of σ1 in the compaction and elasticity stage were observed, and it is due to the sliding of slate along the layered surface. According to the results, the average compressive strength of saturated slates was reduced by 24.3% compared to the unsaturated slates. The spatiotemporal evolution characteristics of AE indicated that the deformation and fracturing of unsaturated slates happened concentratedly and violently in the accelerated crack growth stage, while that of saturated slates occurred with low energy and uniform distribution spatially and temporally in the whole process. Moreover, water content reduced the brittleness index of unsaturated slate by 17.1%. For both conditions, the abundance of AE activity before failure shifted from a high level to a low level and lasted until failure. This can be used as a preliminary failure prediction of slates.

Russia and Finland: Petrographic collections of N.G.Nordenskiöld in the collection of the Mining Museum

The collection of the Mining Museum of the Mining University in St Petersburg contains a variety of minerals, ores and rocks from almost all corners of the globe. Mineralogical and petrographic collections collected by the outstanding Finnish scientist Nils Gustaf Nordenskiöld are always of particular interest. His petrographic collection, which was received by the museum in 1836 and 1841 from Finland, remained for a long time without due attention. The first collection was delivered to the Mining Museum from N.G.Nordenskiöld in 1836. Now there are 80 items in the petrographic collection of the Mining Museum (two items are missing): basically, these are minerals, various rocks, distributed by the places of finds — the provinces of the Grand Duchy of Finland. Some complexity of linking the sample to a specific place is due to the fact that it is difficult to make out the spelling of a particular locality on the label due to poor handwriting, as well as the use of Latin and Cyrillic letters in one word. Besides, in Finland, many localities still have equal Finnish and Swedish names. It is impossible to predict which option will be used for naming a particular place. There are slightly more than half of petrographic samples in the collection — 49 items, the rest (31 samples) are minerals and ores. It is actually a mixed, combined, author’s collection. The second petrographic collection from N.G.Nordenskiöld entered the museum in 1841. The research of the collection recorded as “Finnish marbles” including 23 items was carried out. The “marbles” were selected on a regional basis. Materials were taken for the manufacture of grinds in order to more thoroughly study their petrographic composition. As a result of the research of the grinds, it was not possible to unambiguously determine the “marble”. The collection identified: 10 items of marble, 9 items of limestones, 2 items of sandstones. Single samples of dolomite and slate were also identified. The author concludes that the collections of N.G.Nordenskiöld, the father of Finnish mineralogy, the founder of the Finnish Scientific Society, head of the Mining Department, must be preserved in the Mining Museum in its entirety, “without fragmentation”.

Kinematics and Ar–Ar illite age of deformation in the late Paleozoic Chicomuselo Fold-Thrust Belt (CFTB), Chiapas, Mexico and tectonic implications

The Chicomuselo fold-thrust belt (CFTB) is perhaps the less known cover orogen in Mexico. It is exposed in southernmost Mexico, Guatemala and Belize, along a fringe of about 500 km long and 50–100 km wide, on the southern edge of the Maya tectonostratigraphic terrane. The CFTB is constituted by a succession of sedimentary late Paleozoic marine rocks that include the Santa Rosa Inferior, the Santa Rosa Superior, the Grupera and the Paso Hondo formations. Based on the fossil content of the Santa Rosa Inferior and Paso Hondo formations, the age of these units was constrained from the Mississippian to the late Wolfcampian (early Permian). These successions are folded and thrusted, affecting the two more competent upper formations, whereas the two finer-grained lower units are also highly foliated. Folds, thrusts, and axial-plane foliation (S1) are more consistent with a NE-SW shortening direction and the asymmetry indicates a vergence towards the NE. Such structures are unconformably covered by red-beds of the Middle Jurassic Todos Santos Formation. No angular unconformity was found among the Paleozoic formations, as reported in previous works, which indicates that shortening deformation may have occurred in an orogenic cycle that took place between the latest Permian and Triassic. Structures related to such deformation are cut by kink bands and lateral faults (both dextral and sinistral), spaced across the belt. In order to constrain the thermal conditions of deformation in the CFTB, about 53 samples of phyllite, slate and shale were collected, and their illite crystallinity index (ICI) determined along the belt axis. Calibrated ICI's indicate that deformation occurred between low epizone to the upper diagenetic zone (Kübler index between 0.2 and 1 Δ°2θ angle), with a slow increase in crystallite size from the lower to the upper units, along and across the belt. Deformation-related illite from the Santa Rosa Inferior and Paso Hondo formations was dated with the 40Ar-39Ar method. In the first sample, mica fish of tens of microns dominate the fabric, though a finer-grained illite parallel to the axial plane of late kink bands overgrows such fabric. In the second sample, only one generation of micrometric size illite is visible under the SEM. However, the characterization and dating of several clay size fractions (0.2–0.5, 0.5–1 and 1–2 μm, in addition to 2–4 μm in the first sample) indicate that both samples contain the same two end-member generations of illite, one formed during a first event of intense shortening at 252.3 ± 8.1 Ma, and another associated to spaced faulting formed at 175.1 ± 6.5 Ma. All these data indicate that all sedimentary units within the CFTB were shortened simultaneously during an orogeny that started in the Permian-Triassic threshold and were presumably affected by Middle Jurassic faulting during the opening of the Gulf of Mexico.

Study on the Fractal Model of Erosion of Soft Rock by Water Immersed: Case Study Erosion of Metamorphic Slate

One of the characteristics of soft rock that contains clay and engineering geology is water swelling and.disintegration. The fractal model of slate disintegration is established by Gate Gaudin Sehuhmann distribution function, representative slate samples are chosen to perform laboratory tests of slaking, and the fractal dimension value of slate disintegration change law with time is obtained. The results show that absorbing water and disintegrating progress of slate is also a progress that fractal dimension of slate scrap change successively, when disintegrating of slate arrived to some extent, grade of scrap of slate disintegrated is no more change, fractal dimension of scrap of slate disintegrated incline to a critical value. The disintegration of slate has lag phenomenon in time. The initial disintegration time and the maximum disintegration fractal dimension of rocks are different because of the different microstructure and material composition.

Discrete element modelling of rock creep behaviour using rate process theory

Rock creep behaviour is crucial in many rock engineering projects. Different approaches have been proposed to model rock creep behaviour; however, many cannot reproduce tertiary creep (i.e., accelerating strain rates leading to rock failure). In this work, the distinct element method (DEM) is employed, in conjunction with the rate process theory (RPT) of M.R. Kuhn and J.K. Mitchell (published in 1992) to simulate rock creep. The DEM numerical sample is built using a mixture of contact models between particles that combines the Flat Joint Contact Model and the Linear Model. Laboratory uniaxial compression creep tests conducted on intact slate samples are used as a benchmark to validate the methodology. Results demonstrate that, when properly calibrated, DEM models combined with the RPT can reproduce all creep stages observed in slate rock samples in the laboratory, including tertiary creep, without using constitutive models that incorporate an explicit dependence of strain rate on time. The DEM results also suggest that creep is associated with damage in the samples during the laboratory tests, due to new microcracks that appear when the load is applied and maintained constant at each loading stage.

Definition of Roofing Slate Lithotypes for an International Roofing Slate Classification

The term “roofing slate” comprises all natural rocks that can be used for roofing. Some of the characteristics that define their performance as construction materials are water absorption, bending strength, mineral composition, and aesthetics. From a sustainability point of view, roofing slates also have the largest life expectancy and lowest carbon emissions of all covering materials. This work reviews the constructive characteristics of roofing slates, from technical data provided by producers from all over the world. These data, supported by the petrological characterization of several roofing slate samples, are used to propose a general classification for this special type of rock. Thus, roofing slates are sorted in twelve lithotypes, depending of their petrographical characteristics, defined by the color. The resulting classification is named International Roofing Slate Classification (IRSC), formally defined in this paper.

Size Effects in a Transversely Isotropic Rock Under Brazilian Tests: Laboratory Testing

A transversely isotropic rock, slate, was utilized to investigate the size effect and anisotropy on its deformation, tensile strength, and failure mechanism. A series of Brazilian tests were conducted on slate samples of six different sizes from 25 to 100 mm in diameter at seven different loading-foliation angles from 0° to 90°. The results indicate that the Young’s modulus in the plane of transverse isotropy increases, while the Young’s modulus and shear modulus perpendicular to the plane of transverse isotropy decrease with specimen size. The tensile strength of the slate increases with increasing loading-foliation angle, the variation of which is well captured by the Nova–Zaninetti criterion. Furthermore, the tensile strength of the slate increases with specimen size at loading-foliation angles from 0° to 45°, while it increases first and then decreases with specimen size at loading-foliation angles from 60° to 90°. A unified size-effect relation including two equations is proposed and verified against the experimental data on slate. The size-effect relation reveals the relationship among the tensile strength, specimen size, and loading-foliation angle for the transversely isotropic rock. Finally, the slate samples exhibit an increased brittle failure with specimen size, which is consistent with the observations in various isotropic rocks. It is also found that the specimen size, loading-foliation angle, and loading configuration together control the failure mechanism of transversely isotropic rocks in the Brazilian test.

Investigations of P-Wave velocity, mechanical behavior and thermal properties of anisotropic slate

Rock anisotropies are an important indicator for design and construction of various engineering projects across the world. To investigate the anisotropic characteristics of P-wave velocity, mechanical behavior and thermal properties, laboratory tests were performed on slate samples with various foliation orientations with respect to horizontal direction. The results indicate that the uniaxial compression strength (UCS) exhibits a typical U-type trend, the Young's modulus first decreases and then increases, and the variation of Poisson's ratio shows an opposite trend with the variation in Young's modulus. The anisotropy in strength is greater than that in deformation. Three typical failure modes, i.e. splitting across the foliation planes, shearing and sliding along the foliation planes, and axial splitting failure along the foliation planes, were observed. Scanning electron microscope (SEM) was also applied to analyze the microscopic failure mechanisms. It shows that the slate anisotropies are intrinsically attributed to the directional arrangement of mineral compositions observed by polarizing microscope. P-wave velocity and thermal conductivity both increase with increasing foliation angle, but the linear coefficients of thermal expansion show a decreasing trend. A new empirical formula was then proposed for describing the P-wave velocity and thermal parameters with respect to foliation angle of slate. It displays the empirical predictions match the laboratory measurements. The obtained results can better facilitate our understanding of mechanical behavior and thermal properties of anisotropic rocks, which should be considered in underground engineering applications in layered strata.