Sandstone Research Articles

Old Red Sandstones in the Middle Devonian of Estonia: where are the trace fossils?

Old Red Sandstones in the Middle Devonian of Estonia: where are the trace fossils?

Mechanical Properties and Constitutive Model of Red Sandstone Under Acid Corrosion

Mechanical Properties and Constitutive Model of Red Sandstone Under Acid Corrosion

Failure behaviors of square-tunnel-structured rock specimens under various inclined boundary stress conditions

In most engineering practices, the directions of geo-stress are not always perpendicular or parallel to the center line of underground tunnels’ cross section, and the surrounding rocks are subjected to inclined boundary stresses, which is often ignored in most previous studies. The investigations on the failure characteristics of surrounding rocks around tunnels under inclined boundary stresses have great practical significance. In this study, a series of uniaxial or biaxial compression tests were conducted using cubic red sandstone specimens with different prefabricated square holes. The horizontal centerline inclinations of square holes were designed as 0°, 15°, 30°, and 45°. The test results show that the horizontal centerline inclinations of holes have a great impact on the strength of rock specimens which tend to increase firstly and followed by decreasing. The confining pressure stress σ2 amplify the horizontal centerline inclination effect of holes on the strength of rock specimens. In addition, the horizontal centerline inclination of holes also affected the failure mode and crack propagation of surrounding rock significantly, the stress concentration zone at the right-angle boundary of the hole can induce the propagation of cracks. The findings of this study may provide theoretical guidance and reference significance for the stability evaluation, support parameter and disaster control of underground tunnels.

Age of the basal ‘Lower Old Red Sandstone’ Stonehaven Group of Scotland: the oldest reported air-breathing land animal is Silurian (late Wenlock) in age

The basal upper Silurian–Lower Devonian ‘Lower Old Red Sandstone’ deposits of the Midland Valley of Scotland contain several important fossil biotas, including that from the Cowie Harbour Fish Bed. This biota is of great significance because it represents one of the oldest known examples of a fossilized terrestrial ecosystem and includes the oldest reported air-breathing land animal (the myriapod Pneumodesmus newmani Wilson and Anderson, 2004 ). Based on biostratigraphical evidence from dispersed spores this biota is dated as late Wenlock (late Silurian) in age. Recently, however, this age constraint was challenged, based on 238 U– 206 Pb radiometric analysis of zircons, and it was proposed that these deposits are much younger (Early Devonian: Lochkovian). This proposal has serious implications regarding (1) the composition and nature of early terrestrial ecosystems and (2) the geological setting with respect to the timing of terrane accretion and the onset of ‘Lower Old Red Sandstone’ sedimentation. We report on newly discovered dispersed spore assemblages and additional zircon data that confirm a late Wenlock (late Silurian) age. This age designation establishes the importance of the biota of the Cowie Harbour Fish Bed and is more compatible with both its biotic composition and the regional geological setting.

Size effect of anisotropy in spatial variability of rocks: evaluation through digital drilling

Evaluating the anisotropy of rock and its size effect in spatial variation is of great significance for improving engineering efficiency and stability. For this purpose, an anisotropy index is used to quantify the magnitude of anisotropy in rock. Digital drilling tests are carried out in three directions on six types of rock to investigate the anisotropy of drilling parameters. The rock is subdivided into multiple small units along the depth of drilling, and the effect of size on rock anisotropy based on drilling work was studied. The research findings indicate that the drilling work on six rock types exhibits anisotropy, and the anisotropy sequence for the total drilling work of each rock is as follows: red sandstone > granite > slate > gneiss > sandstone > argillaceous sandstone. As the length of rock units increases, the anisotropy index of drilling work initially exhibits a fluctuating trend, subsequently reaching a state of stability, thereby manifesting a size effect. Furthermore, the representative elementary volume (REV) for each type of rock exhibits distinct variations. The anisotropy indices for drilling work along the depth of the borehole exhibit an initial phase of rapid increase, followed by a convergence towards a value close to 1.0. The anisotropy of rocks demonstrates size dependence, and size effects also exhibit anisotropy. Anisotropy and its size effects are interconnected and inseparable. The reliability of the cited anisotropy index is checked by comparison with two other anisotropy indices. This comparison shows that our method can reliably determine rock anisotropy. In summary, the research outlined in this paper presents a highly efficient and straightforward approach to evaluate the effect of size on rock anisotropy.

Mechanical properties of fracture-grouted prefabricated sandstone after thermal-acid coupling treatment: An experimental study

Grouting reinforcement is an efficient approach to increase the stability of engineered fractured rock masses that may be subjected to high temperatures and acidic groundwater in complex geological environments. To reveal the mechanical properties and failure characteristics of the grout-reinforced fractured rock masses under thermal-acid coupling conditions, prefabricated fractured red sandstone specimens with different inclination angles (IAs) were firstly grouted using a new high-strength fast anchoring agent (HSFAA). Then, the grout-reinforced specimens (GRSs) were then immersed in hydrochloric acid (HCl) solutions with different temperatures (varying from 25 to 300 °C). Finally, the macroscopic mechanical properties, microscopic morphology, and crack evolution characteristics of the GRSs after thermal and acid solution treatments were investigated by the uniaxial compression test, X-ray computed tomography (CT) and scanning electron microscopes (SEM). The results confirmed that the HSFAA featured with high fluidity, rapid setting, excellent early strength, and micro-expansion, was an ideal grouted reinforcement material for fractured rock masses. The compressive and tensile strengths of the HSFAA material at a 1-day curing were 2.01 and 1.64 times those of the ordinary Portland cement 42.5 (P.O 42.5), respectively. The fractured IA, thermal-acid coupling method and temperature affected the mass loss, strength parameters, and failure modes of the GRSs to different degrees. The thermal-acid coupling treatment affected the initiation location and extension direction of cracks within the GRSs. The increasing temperature led to the larger and more varied internal cracks, as well as the more complex 3D spatial morphology within the GRSs.

Characterization of the creep behavior and modeling considering viscoelastic-plastic damage of quartz sandstone under thermo-hydro-mechanical conditions

Characterization of the creep behavior and modeling considering viscoelastic-plastic damage of quartz sandstone under thermo-hydro-mechanical conditions

Inversion study on elastic–plastic material parameters of red sandstone in uniaxial compression test

In order to obtain the real material parameters of heterogeneous rock, the material parameters of red sandstone specimens under uniaxial compression tests are inverted based on the Digital Image Correlation (DIC) method and the Finite Element Model Updating (FEMU) method. The DIC method is employed to calculate the displacement field of red sandstone specimens during uniaxial compression loading. Concurrently, a uniaxial compression elastic–plastic finite element numerical model with non-uniform material parameters is developed based on the FEMU method. The model adopts the Mohr–Coulomb yield criterion and adjusts the boundary conditions in real-time to maintain consistency with the test. The vertical displacement field of the numerical model is juxtaposed with that of the test to construct the objective function. Optimization is achieved using the Artificial Fish Swarm algorithm, which enables the acquisition of the non-uniform distribution and evolution process of the material parameters of specimens at different loading moments. The results indicate that this method can spatially obtain the non-uniform distribution field of material parameters and temporally track the evolution of material parameters during the loading process. This research lays a solid foundation for enhancing the accuracy of intelligent coal mining and dynamic disaster monitoring and early warning in coal mines.

Study on the Influence of Sample Size on the Mechanical and Integrity Characteristics of Coal Measure Sandstone under High Strain Rate

In order to explore the size effect of the mechanical and damage characteristics of coal measure sand stones under dynamic load, uniaxial impact compression tests were carried out on coal-bearing sand stones with a diameter of 50 mm and a length–diameter ratio of L/R = 0.5, 0.8, 1, 1.2, 1.5, 1.8, and 2 by using the Hopkinson pressure bar test system. The size effect law of the mechanical properties and energy dissipation of coal-bearing sandstone under a high strain rate were investigated. Then, the mercury injection test was carried out on the fragments at different positions, and the electron microscope scanning test was carried out on the fragments near the end of the transmission rod. Based on the area damage definition method and normalization treatment, the integrity model of coal measure sandstone, considering the influence of the length–diameter ratio, was established. The results showed that the peak strength and dynamic elastic modulus of coal measure sandstone increased first and then decreased with the increase in length–diameter ratio under impact compression load, and they reached the maximum when the length–diameter ratio was 1.2. The dynamic peak strain increased gradually with the increase in length–diameter ratio. The energy of coal-bearing sandstone showed strong size effect, that is, the total absorbed energy, elastic energy, and dissipated energy increased with the increase in length–diameter ratio, and the size effect of total absorbed energy was the most obvious. Under the same impact pressure, the porosity of coal-bearing sand stones with seven kinds of length–diameter ratios near the incident end was roughly the same. But when the length–diameter ratio was greater than 0.5, the porosity decreased gradually with the increase in the distance from the incident end. And the larger the length–diameter ratio, the more obvious the decreasing trend. When the length–diameter ratio was smaller, the size of the holes and cracks and the cluster density were larger. The integrity model of coal measure sandstone, considering the influence of the length–diameter ratio, showed that the larger the length–diameter ratio, the better the relative integrity of coal-bearing sandstone.

Investigation of blast-induced rock fragmentation and fracture characteristics with different decoupled charge structures

Decoupled charge structure is widely employed in profile and production blasting of rock engineering, and its breakage effectiveness is closely linked to the utilization rate of explosion energy. In this investigation, the failure patterns and damage extent of cubic red sandstone specimens induced by blasting with various decoupled charge modes were examined through two groups of laboratory tests, and a three-parameter generalized extreme value (GEV) function was introduced to quantify the rock fragmentation size distribution (FSD) characteristics. Moreover, the Riedel-Hiermaier-Thoma (RHT) model parameters were calibrated based on the blasting test result of the R1 sample. Building upon this validated model, dynamic fracture behavior and pressure attenuation process in a dual-hole blasting finite element model with radial and axial decoupled charge structures were reproduced. Notably, the effects of delay time and initiation mode as well as coupling medium on the effectiveness of rock breakage were discussed. The results demonstrated that the three-parameter GEV function offers a more accurate characterization of the FSD features after rock blasting. Additionally, it is observed that the average fragment size decreases linearly with a reduction in the decoupling ratio, leading to a tendency for finer fragments and more uniform FSDs. Besides, through a comparative analysis of energy distribution characteristics and the volume of destruction in various coupling mediums for rock blasting, it is found that water, as a coupling medium, exhibits the highest energy transfer efficiency, followed by wet sand and dry sand, while air shows the least energy efficiency. Furthermore, the theoretical result of the stress transmission coefficient computed using the equivalent wave impedance method can proficiently reflect the extent of rock fragmentation in decoupled charge blasting.

Application of Electrical Resistivity Method to Decipher Groundwater Occurrence Status at Isikuku, Southern Nigeria

Electrical resistivity method is a type of geophysical survey employed for groundwater investigation, conducted in Isikuku Community in Benin City, Edo state with the aim of delineating groundwater occurrence. Schlumberger electrode array configuration was employed in this study. Six (6) VES points were surveyed with linearised inversion technique used for the interpretation of sounding taken at various locations in the area. The data collected were interpreted by curved matching and computer iteration using Interpex Ix1D v 2 software. From the geoelectric section, VES 1 possess the AK curve with four layers ρ1˂ρ2˂ρ3˃ρ4, VES 2 possess the KQ curve with four layers ρ1˂ρ2˃ρ3˃ρ4, VES 3 possess the A curve with three layers ρ1˂ρ2˂ρ3, VES 4 possess the AK curve with four layers ρ1˂ρ2˂ρ3˃ρ4, VES 5 possess the A curve with three layers ρ1˂ρ2˂ρ3, VES 6 possess the K curve with three layers ρ1˂ρ2˃ρ3. Geo-electrical layers identified in the study area included topsoil, sandy clay, clay basement and sandstone. The VES study revealed the layer which constitute the productive water-bearing zones referred to as good groundwater potential aquifers. The analysis of the interpretation of the field data showed that the area under investigation delineated four layers earth in each of the vertical electrical sounding point. Generally, the geoelectric survey conducted in the study area revealed the subsurface lithologies: Clay, Clayey Sandstone, Sand stone, Coarse Sand, Lateritic soil and Top soil. Thus, vertical electrical sounding techniques employed in this study has proved useful and successful in delineating subsurface lithology in the study area.

Cracking behaviors and mechanism of pre-cracked rock specimens under coupled THM fields with chemical processes

In deep rock engineering, natural cracks in rock mass subjected to thermo-hydro-mechanical-chemical (THMC) loads have tendency to initiate and propagate, and result in potential safety hazards. Current literature on cracking behaviors and mechanism of pre-cracked rock under multi-field loads is focused on single (M), two (TM, HM) or three fields (THM, HMC), less on THMC fields. In this study, a series of self-designed triaxial compressive tests were performed to study different THMC fields influencing on mechanical behaviors and failure patterns of pre-cracked red sandstone specimens. A new THMC fracture criterion, recently proposed by our group team, is used to further analyze the crack initiation mechanism of red sandstone under THMC loads. Research results suggest that the stress-strain curve is greatly influenced by the temperature, confining pressure and acidity and alkalinity of chemical solution, but relatively less by the hydraulic pressure. As the temperature and hydraulic pressure increase, the confining pressure decreases, and the acidity or the alkalinity of chemical solutions becomes strong, both the elastic modulus, crack initiation stress and peak strength of specimen are decreased, and the failure pattern is changed from shear failure to tensile failure. The crack initiation stress and peak strength usually have the largest, middle, smallest values in the shear, tension-shear and tensile failures, respectively, while the peak strain has largest value in the mixed tensile-shear failure. The acid solution has greater weakening effect than the alkaline solution with the same concentration. Theoretical results indicate that the temperature and chemical fields influencing on crack initiation is mainly attributable to its weakening of rock fracture toughness, while seepage and stress fields on crack initiation to its change of the stress state at crack-tips. The THMC mechanism of crack initiation can be well revealed by the new THMC fracture criterion.

Morphological damage and strength deterioration of red sandstone under freeze–thaw cycles

Insight into the growth of internal microstructure and surface morphology is critical for understanding the robustness of red sandstone artifacts in frigid environments. Since freeze–thaw (F-T) cycles can exacerbate the surface deterioration of water-bearing sandstone, a series of investigation on fresh and weathered water-bearing sandstone samples with different F-T cycle numbers (i.e. 0–100) is performed in this study, including three-dimensional (3D) laser scanning, scanning electron microscope (SEM) and computed tomography (CT) scanning tests, thermal property tests, Brazilian tests, and multi-field numerical simulations. Our results demonstrate that with increasing F-T cycles, the surface fractal dimension and specific surface area of red sandstone samples increase, and the pore size distribution inside rocks shifts from ultrananopores (10–100 nm) to micro-pores (0.1–100 μm) and ultramicropores (100 μm+). Spatially, the pores generated by the F-T cycles are more prominent near the surfaces of rock samples. Numerical simulation indicates that the uneven pore distribution leads to surface degradation. After 100 F-T cycles, the intergranular (IG) cement of the samples cracks, and the IG fractures are widened; eventually, due to the structural integrity weakening, the tensile strength is drastically reduced by over half. The thermal properties of the water-saturated sandstone can be improved during the F-T cycles, and a strong coefficient of determination of 0.98 exists between the fractal dimensions of sandstone surface and the tensile strength. When assessing the mechanical properties of stone artifacts under F-T cycles, the morphological damage of red sandstone should first be investigated when in situ sampling is inappropriate.

TRANSCENDENT SCULPTURES: EXPLORING THE EIGHT-FOLD PATH OF BUDDHISM THROUGH INNOVATIVE ARTISTRY

Some artists draw inspiration from their personal experiences, emotions, and perspectives, and may use their art as a means of expressing their innermost thoughts and feelings. Other artists may be interested in capturing the beauty of nature, exploring the human form, or delving into social and political issues. Some artists may be motivated by a desire to create visually stunning or thought-provoking works, while others may be more focused on creating pieces that reflect their cultural or historical identity. Ultimately, Artists' subject matter choices can be influenced It is influenced by a number of factors, including their personal characteristics interests and experiences, their artistic goals and vision, and the broader cultural and social context in which they live. Over the course of history, artists have explored the Eight-fold Path philosophy of the Buddha in a variety of mediums. If an artist were to choose this as a subject for their work, they could approach it in a number of different ways. The artist could explore the challenges and triumphs of following the path, as well as the trans-formative power of enlightenment.Regardless of the approach taken, an artist who chooses the Eight-fold Path as a subject for their work would have a rich and meaningful philosophical tradition to draw from, offering endless possibilities for creative expression and interpretation. There is a new dimension to right thinking, right speech, right memory, right livelihood, as well as right exercise and right samadhi. A combination of black marble and sand stone has been used to create the sculptures.

Shocked quartz in sandstone from the buried Ilkurlka impact structure, Officer Basin, Western Australia

AbstractThe Ilkurlka structure is an ~12 km diameter buried circular aeromagnetic anomaly within the Officer Basin in Western Australia. Prior studies postulated a range of origins, including meteorite impact. We report the presence of pervasive deformation in the first drill cores from the structure. Brecciated sandstone and siltstone contain arrays of quartz grains with concussion fractures and rare shocked quartz grains with planar deformation features (PDF). Universal stage measurements of two quartz grains reveal one grain with PDF parallel to (0001) orientation and three PDF sets parallel to . A second grain contains three PDF sets parallel to and one set parallel to . The shocked grains are interpreted to have formed in situ, rather than representing transported detrital shocked grains. These results suggest local shock compression of at least 10 GPa; however, preservation of primary porosity and overall paucity of shocked grains may indicate lower mean shock pressures. (U‐Th)/He dating of 58 apatite grains from four samples across both cores shows a dominant age population at ~265 Ma and a minor age population at ~135 Ma. These dates overlap with regional events and thus do not provide an unambiguous impact age. An upper Carboniferous to lower Permian maximum impact age is provisionally proposed based on inferred missing target rock stratigraphy.

Wireline log stratigraphy of the lower Cambrian Læså Formation, Bornholm, Denmark.

A detailed correlation of the lower Cambrian Læså Formation on southern Bornholm, Denmark, is based on gamma ray and formation resistivity wireline logs from 25 water supply wells and 5 scientific boreholes. The interpretation hinges on comparison with the wireline log suite obtained in the fully cored Borggård-1 borehole that penetrated the formation in its entirety. The Norretorp Member, 102.9 m thick in Borggård-1, consists predominantly of intensively bioturbated siltstone. Several levels are strongly glauconitic and usually also contain phosphorite nodules. Fine-grained sandstone beds, 0.5–20 cm thick and interpreted as tempestites, occur throughout the unit; a few thicker sandstone layers consist of stacked tempestites. However, many sandstone beds, primarily in the upper 2/3 of the member, have been partly or totally obliterated by the pervasive bioturbation. The overlying Rispebjerg Member, 3.5 m thick in Borggård-1, is dominated by well-cemented medium to coarse-grained quartz sandstone. The variable lithology of the Læså Formation is illustrated by photos of core samples from Borggård-1. The studied wells are located on different fault blocks with 18 km between the easternmost and westernmost well sites. The Norretorp Member is of almost similar thickness throughout the study area whereas the Rispebjerg Member is 2.2–5.6 m thick. The essentially unchanging thickness of the Læså Formation and the sheet like distribution of tempestites demonstrate that the intense faulting of southern Bornholm post-dates deposition. The Norretorp Member is divided into a lower log-unit (57 m thick in Borggård-1) characterized by a moderately variable gamma ray log pattern and an upper log-unit (46 m thick in Borggård-1) exhibiting a more uniform gamma radiation of overall lower intensity. The log-units reflect a more common occurrence of glauconite and phosphorite in the lower part of the member and a higher sand content in the upper part. These lithological differences are also reflected by a generally higher resistivity and P-wave velocity in the upper log-unit. Seven thicker sandstone horizons (15–80 cm thick), labelled S1 to S7, are laterally persistent within the Norretorp Member. Four additional horizons, referred to as MGL [multiple gamma low], MGH [multiple gamma high], MM [middle marker] and GH [gamma high], are also laterally widespread. A readily identifiable red-brown horizon is located at 4.4–5.9 m above the base of the Læså Formation in Borggård-1: it appears to be developed throughout the study area.

A new method for predicting multi-crack fracture mechanism in the finite plate of red sandstone

A novel theoretical approach was put forth to forecast multi-crack propagation trajectories in a finite plate. First, a weighted residual approach and complex function are used to create the formula for computing the maximum (stress intensity factor) SIF of multi-crack in the finite plate. And then, three cracks were then chosen as a model for computation to determine how the plate size affects the SIF. The formula of multi-branch crack in finite plate is derived and the crack initiation and propagation criterion of multi-crack in finite plate was established. Finally, the propagation paths of three cracked red sandstone in a finite plate were predicted and verified by the uniaxial compression test. It demonstrates that the SIF of multiple cracks in a finite plate is consistently larger than that of an infinite plate. Under the uniaxial compression test, the first crack initiation point is often A2 or B2, and each specimen’s first crack initiation time increases and subsequently reduces when the relative horizontal spacing (Ds’) of cracks varies. The crack initiation stress increases and the unstable stress first increases and then decreases with Ds’. The total crack extension length initially goes down and then goes up. All of the fracture initiation and propagation mechanisms are Mode I. The effectiveness of the multi-crack propagation theory in finite plates is established by the good agreement between predicted and test findings.

Mesoscopic Damage and Fracture Characteristics of Hard Rock under High-Frequency Ultrasonic Vibration Excitation

Ultrasonic high-frequency vibrational fracture technology can compensate for the deficiencies of traditional fracture methods and has promising applications in underground rock drilling engineering. In this study, ultrasonic high-frequency vibrational tests were performed on brittle fine-grained red sandstone in combination with CT real-time scanning, which revealed mesoscopic fracture processes in the rock. Digital image processing technology is used to identify and extract the pores of CT images, and the pore evolution law of rock slices at different layers under ultrasonic vibration excitation is quantitatively studied. The results show that the increase in porosity decreases with increasing distance from the excitation surface, with the lowest layers of the rock showing an increase in porosity of only 0.22%. In addition, a mechanical model of rock breaking by ultrasonic vibrations was derived to explain the non-uniform damage mechanism of rock space under ultrasonic vibration excitation.

Mechanism of strength deterioration of red sandstone on reservoir bank slopes under the action of dry–wet cycles

To investigate the micro-scale mechanism of strength deterioration under different times of dry–wet cycles, laboratory tests of physical properties, triaxial compression, X-ray diffraction (XRD) and scanning electron microscopy (SEM) were conducted on red sandstone on reservoir bank slopes. The research results showed that when the 5th dry–wet cycle ended, the dry mass and peak strength started to rapidly decline, while the porosity and saturated mass increased rapidly. In general, all of these behaviours become relatively stable when the number of cycles increased. Similarly, cohesion and internal friction angle changed most significantly from 0 to 10 cycles and then became stable. In addition, the physical expansion of the adsorbed water film and the dissolution and expansion of mineral particles increased the number of internal microcracks and pores and the porosity and saturated mass of the sample. In addition, the pore fluid effect and fracture flow effect made the microcracks in the red sandstone grow and connect; thus, the peak strength of the sample decreased. Moreover, during the dry–wet cycles, the change in the relative content of mineral particles and the pore fluid effect weakened the clay cementation, and then the dry mass and cohesion of the samples decreased. The research reported in this paper will play a very significant role in the scientific analysis of slope stability in the Three Gorges Reservoir area.

Factors influencing the evolution of sandstone sea caves: A case study from the Apostle Islands National Lakeshore (Lake Superior, USA)

Caves in coastal cliffs in the Apostle Islands were analyzed for factors controlling their origin and evolution. Even though the Bayfield Group quartz sandstones were found to be of relatively low tensile strength, the traditional explanation attributing speleogenesis to localized zones of lithological and tectonic weakness does not adequately explain all geomorphic features of the caves. The caves were found to be formed by coalescence of smaller arcade-shaped cavities serially developed along subhorizontal discontinuities. In concordance with the previously formulated “arcade principle”, positions and shapes of the cavities are defined by areas of reduced stress within the gravity-induced stress field. Evacuation of material from the rock massif can be attributed to wave action including the effect of water-pressurized air, and frost action. Compound cavities above the discontinuities tend to form “higher-order” arcade-like cavities/caves while those beneath more resistant strata rather develop into elongated overhangs similar to ordinary coastal notches. Propagation of the largest cavities, formed along steeply dipping joints and faults, is attributed to mass wasting and roof collapses. Similar examples of discontinuity-related cavities in coastal settings, suspectedly also controlled by gravity-induced stress distribution, can be found worldwide, being mostly concentrated to areas covered by ice sheets in the Pleistocene. The interplay between post-glacial isostatic uplift and Holocene lake-level rise is responsible for the development of mature forms of coastal caves in the Apostle Islands where present cliffs are estimated to have been exposed to the effects of wave action for the last 3–5 ky.