Sandstone Research Articles

Study on fatigue characteristics of red sandstone under extremely high stress in the hydro-chemical environment

To study the failure of red sandstone under extremely high stress during the service life of tunnels, an in-depth study was conducted on the mechanical properties of red sandstone under uniaxial loading and cyclic loading and unloading processes at different pH values using the AG-250kNIS electronic precision material testing machine and MTS815 mechanical testing machine. The results show that as the acidity and alkalinity increase, the peak stress under uniaxial loading decreases and the axial strain increases,The peak stress at failure is 9.40, 12.37, 7.18, and 5.36 MPa, respectively, accounting for 74.19%, 68.91%, 40.38%, and 36.21% of the uniaxial compressive strength; The number of cycles significantly decreases during cyclic loading and unloading fatigue failure, and the stress required for sandstone failure gradually decreases. The peak strength and elastic modulus of sandstone show a decreasing trend, indicating that the hydrochemical environment plays an accelerating role in rock degradation. During the cyclic loading and unloading process of sandstone, there is a continuous increase in dissipated energy and finally a sudden increase, the Ud/U and Ue/U ratios at the peak point of sandstone in the natural state are 0.399 and 0.601, respectively, while the overall elastic energy shows an increasing trend; and a damage evolution model was established based on dissipative energy, which can better describe the degradation process of red sandstone.

Mechanical properties and energy evolution of thermally damaged red sandstone in high-strain-rate impact tensile tests: Experimental and theoretical analyses

The dynamic tensile strength of rocks affects structural stability in geotechnical applications requiring thermal resilience. This study employs a large-diameter (Φ75 mm) split Hopkinson tension bar (SHTB) to perform high-strain-rate tensile tests on red sandstone specimens subjected to thermal treatments at temperatures up to 1200 °C. However, specimens heated to 1200 °C transitioned to an amorphous melt phase, making tensile tests infeasible. The novel large-diameter SHTB technique improves the test efficiency by using double reinforcement and an adhesive to attach the specimen to the bar. An energy-based damage variable and a comprehensive rock brittleness index are used to assess the effects of the strain rate and thermal conditions on the specimens' mechanical behavior and energy dissipation. Further, an innovative dissipated energy model (TII) describes the intrinsic nonlinearities of the rock's dissipated energy dynamics and their crucial influences on the pre-peak stress responses. A dual-threshold model is utilized to describe thermal strengthening or weakening, revealing fundamental insights into the energy mechanics of rock failure, which are vital for the integrity of high-temperature geotechnical systems.

Was the Stonehenge Altar Stone from Orkney? Investigating the mineralogy and geochemistry of Orcadian Old Red sandstones and Neolithic circle monuments

Recent petrological, mineralogical and geochemical investigations of the Stonehenge Altar Stone have negated its source in the Old Red Sandstone (ORS) Anglo-Welsh Basin. Further, it has been suggested that it is time to look wider, across northern Britain and Scotland, especially in areas where geological and geochemical evidence concur, and there is evidence of Neolithic communities and their monuments. In this context the islands of Orkney, with its rich Neolithic archaeology, are an obvious area worthy of investigation. The same techniques applied to investigations of the Altar Stone and ORS sequences in southern Britain have been applied to two major Neolithic monuments on Mainland Orkney, namely the Stones of Stenness and the Ring of Brodgar. In addition, field samples of ORS lithologies from the main stratigraphic horizons on Mainland Orkney have been investigated.Portable XRF analyses of the five exposed stones at the Stones of Stenness and seven of the exposed stones at the Ring of Brodgar show a wide range of compositions, having similar compositions to field samples analysed from both the Lower and Upper Stromness Flagstone formations, with the stones at Stenness appearing to have been sourced from the Upper Stromness Flagstone Formation while the Ring of Brodgar stones possibly being sourced from both formations. Examination of the mineralogy of ORS field samples and the Stonehenge Altar Stone, using a combination of X-ray diffraction, microscopy, Raman spectroscopy and automated SEM-EDS shows there to be no match between the Orkney samples and the Altar Stone. Only two samples from Orkney showed the presence of baryte, a characteristic mineral of the Altar Stone. Another key discriminant is the presence of abundant detrital K-feldspar in all of the Orkney field samples, a mineral which has only very low abundance in the Altar Stone. In addition, the regularly interstratified dioctahedral/dioctahedral smectite mineral tosudite is present in the clay mineral assemblage of the Altar Stone, but not detected in the Orkney samples.It is concluded that the Altar Stone was not sourced from Mainland Orkney, despite considerable evidence for long-distance communications between Orkney and Stonehenge around 3000/2900 BCE.

Experimental investigation of permeability evolution and progressive damage of sandstone in the complete process of direct shear

Permeability evolution and damage behavior under shearing conditions are critical for reliable predictions of rock seepage characteristics during excavation and a correct assessment of their impacts on the occurrence of natural or induced hazards. However, publications concerned with this problem have been poorly issued so far. The primary objective of this study is to innovatively investigate permeability evolution and damage behaviors of sandstone in the complete process of direct shear. Several groups of red sandstone specimens are deformed in direct shearing using a newly modified servo-controlled direct shear apparatus to measure permeability evolution and monitor acoustic emission (AE) activities with damage under various normal stress conditions. The morphology of the rupture surfaces is scanned using a 3D laser scanner after tests. According to our experimental results, the locus of the shear stress-displacement curve is found to be closely associated with microcrack progressivity. The initial permeability in advance of shearing test and the peak permeability appearing after the peak shear stress decrease with the increasing normal stress. The minimal and maximum permeability values exhibit a lag-effect with respect to the turning and the peak points on the shear stress-displacement curve. Furthermore, a palpable surge is found in the interevent time function during shearing, which can be a potential indicator for early warning of catastrophic rupture of brittle rock materials under shearing or compression. The joint roughness coefficient (JRC) values in the direction of shearing deformation for each normal stress case are more significant than those in the direction perpendicular to the shear displacement. The impacts of our obtained results are potential ramifications for permeability control in rock engineering projects.

Characterization and differences of acoustic signals response of semi-circular red sandstone under combined monotonous and cyclic loadings

After underground coal mining, rocks are often subjected to tensile damage by the interaction of dynamic and static loadings. The process of rock fracture development under dynamic and static loadings will be released in the form of acoustic energy to form an acoustic signal. In addition, the acoustic signals in dynamic loading differ from that in static loading. Therefore, this study conducted three-point bending experiments with continuous dynamic loading and dynamic–static coupling loading on semi-circular red sandstone specimens. The acoustic signals during red sandstone specimens’ tensile damage were monitored in real-time. The results show that red sandstone’s tensile strength and deformation are enhanced under dynamic–static coupling loading. The red sandstone has a more effective acoustic emission hit rate, energy rate, and r during tensile damage under continuous dynamic loading. In dynamic loading, macroscopic fractures are developed in red sandstone, which has few acoustic emission events but releases strong acoustic signals. In static loading, the pores inside the red sandstone are compacted, the rock particles are rearranged, and the tiny fractures are closed, and its acoustic emission events are many but low in energy. In addition, the rock particles in the front area of the static loading fracture are tightly cemented, which increases the difficulty of separating the rock particles in the front area of the fracture under dynamic loading. Then weakening the red sandstone fracture development process and suppressing its acoustic signals. The research results provide more insight into the differences in tensile damage processes in red sandstone under the interaction of dynamic and static loadings.

Experimental investigation on high voltage electric pulse rock breaking under drilling mud conditions

High voltage electric pulse rock breaking technology is a novel and promising rock breaking technique that is environmentally friendly, efficient, and nearing industrial application. However, the drilling performance of electrode bits under varied drilling muds and the mechanism of high voltage electric pulse rock breaking remain unclear. This study entails real drilling experiments conducted on red sandstone using electrical pulse drilling (EPD) under different initial voltage peaks, electrode bits, and drilling muds to investigate the impact and mechanism of EPD. A laboratory experimental system for high voltage pulse rock breaking is established based on a 0–80 kV EPD pulse generator. Three types of electrode bits are devised, namely, petal-structural, four-point-structural, and circular-ring-structural electrode bits. The EPD experiments on red sandstone are executed under seven different drilling muds at initial peak voltages ranging from 13 to 17 kV. And the efficiency of EPD rock breaking is assessed using five quantitative indexes: rate of penetration, breaking volume, specific energy of rock breaking, and the proportion of electrical fragmentation and hydraulic-electric rock fragmentation. Furthermore, the physical parameters, i.e., density, conductivity, Zeta potential, PH, and apparent viscosity, of the seven drilling muds are measured, shedding light on the rock breaking mechanism of EPD under specific drilling mud conditions. Subsequently, the designed electrode bit is evaluated, and based on experimental phenomenon, structural optimizations of the electrode bit and EPD drilling recommendations under various drilling mud conditions in real drilling scenarios are proposed. This research is poised to offer valuable insights into the design of EPD electrode bits and the selection of drilling mud for enhancing drilling efficiency.

Evidence of a Large Debris Avalanche Event (22.0 Ma) from the Comondú Group on the Baja California Sur Peninsula, Mexico

The morphological, sedimentological, and microtextural characteristics of Miocene debris avalanche deposits which extend from the Punta Coyote to the vicinity of the city of La Paz, were studied along the eastern of the Baja California Peninsula. The debris avalanche deposits studied include a mixture of angular mega blocks whose composition comes from the deposits that make up the Comondú Group: pre-Comondú (red sandstones and conglomerates with intercalated ignimbrites), the Upper Unit (brownish sandstones, shales, and conglomerate), and breccia, with a predominance of jigsaw cracks, injection structures, and fault structures. These deposits were studied and analyzed considering the stratigraphic relationships between the rock formations present in the mega-blocks. Six stratigraphic sections were measured to describe the composition and morphology of the clastic components present in the mega-blocks of the debris avalanche. Two different units (m1 and m2), were identified in the debris avalanche deposits. Unit m1 is the oldest, with a thickness of 100m, and consists of a chaotic set of mega-blocks up to 100 m in diameter derived from the pre-Comondú Group, and Upper Unit. The deposits are highly heterolithic, with angular and highly fractured clasts at different scales. While the unit m2 consists principally of 20-100 m thick volcaniclastic layers dominated by poorly sorted, breccias and minor epiclastic deposits. According to stratigraphic relationships, the collapse occurred at 22.0 Ma. The debris deposit covers an area of 150 km2 and has an estimated volume of 1.3 km3. The characteristic suggests a transport mechanism with a disintegration of the mega-blocks and a contact/collision interaction. Where mega-blocks moved within a dense flow in a buffered manner, remaining consistent over long distances. The observed structures and textures suggest that the mega-blocks were mainly produced by the alteration and ingestion of older substrates by the avalanche of moving debris. The avalanche flowed over pre-existing topography excavated in the Comondú Group sequence, and flow indicators reveal a west-southwest direction, exhibiting a typical mountainous avalanche topography. The study of ancient debris avalanche events not only provides a deeper understanding of these natural phenomena but also contributes to the development of tools to predict, mitigate, and manage risk areas.

Sedimentary provenance of the Upper Devonian Old Red Sandstone of southern Ireland: an integrated multi-proxy detrital geochronology study

The Devonian Old Red Sandstone (ORS) magnafacies of southern Ireland is hosted in the Early Devonian Dingle Basin and the Late Devonian Munster Basin. Following the closure of the Iapetus Ocean during the Caledonian Orogeny, the Dingle Basin developed as a pull-apart structure before being deformed by Acadian tectonic activity. The Munster Basin developed as a half-graben structure in response to post-Acadian north–south extension in the region. Thus, the Irish ORS provides insights into the region's tectonic history owing to its temporal and spatial proximity to the Caledonian ( c . 475–425 Ma), Acadian ( c . 400–390 Ma) and Variscan orogenic events ( c . 390–290 Ma). This study presents the first detrital zircon and apatite U–Pb geochronological data for the Upper ORS (UORS) in southern Ireland in addition to detrital white mica 40 Ar/ 39 Ar geochronological data to help unravel the depositional history of the Irish UORS and to assess the possible role of sedimentary recycling in Late Devonian basin development. Most UORS samples contain few late Neoproterozoic detrital zircon grains and are instead dominated by early Paleozoic and c. 1.1 Ga zircons. These populations represent recycling of northerly-derived Ordovician to Silurian strata of the Southern Uplands–Longford–Down terrane, which are of Laurentian affinity, and not recycling of Lower ORS (which contains a significant number of late Neoproterozoic detrital zircons) as previously thought. Similar detrital zircon dates have been observed in Givetian–Frasnian quartzites of the Pulo do Lobo Zone on the Iberian Peninsula, providing a possible Rheic Ocean link with the UORS.

Uniaxial compressive strength prediction based on measurement while drilling data: A laboratory study

The uniaxial compressive strength is one of the most important basic parameters of rock, which is essential for surrounding rock stability analysis and support scheme design of underground engineering. At present, it is time consuming and costly to take a large amount of core samples for laboratory testing, and the mechanical properties of the cores may be affected by mining disturbance, which can easily lead to inaccurate result. The measurement while drilling (MWD) technology provides a new approach to solve the above challenge. The key to implementing this technology is to establish a correlation model between drilling parameters and rock mechanics parameters. Based on the characteristics of polycrystalline diamond compact (PDC) bits in drilling and rock breakage, this paper analyzes the mechanical state of the bit in breaking rock. A theoretical correlation model between the torque, feed force of the bit and the uniaxial compressive strength of the rock has been developed. To verify the accuracy of the theoretical model, the uniaxial compressive strength of five different types of rocks (red sandstone, green sandstone, limestone, marble and shale) was obtained through laboratory mechanical tests. The torque Mb, feed force Fb and other parameters in the drilling process of these five rocks were tested through the newly developed MWD test system. The correlation between the drilling parameters and the uniaxial compressive strength of rock was established. The results showed that the feed force Fb and torque Mb measured at five different types of rocks indicate a linear increasing trend with an increase in depth of cut h. Meanwhile, a strong linear relationship between the feed force Fb and torque Mb is evident. This paper proposes an MWD-based method to rapidly conduct the in-situ measurement of the uniaxial compressive strength of various rocks.

Research on the Energy Dissipation Characteristics and Stress Wave Spectrum Analysis of Red Sandstone Subjected to Progressive Load Cyclic Impact

Research on the Energy Dissipation Characteristics and Stress Wave Spectrum Analysis of Red Sandstone Subjected to Progressive Load Cyclic Impact

Experimental study on dilatancy behavior of soft rock under dynamic loading

Correct understanding of rock dilatation plays a non-negligible role in the safety of rock engineering and the efficiency of geological resources extraction. Although the significance of dilatation under quasi-static loading or unloading conditions is well-studied, its behavior under dynamic loads remains poorly understood. This is largely because conventional dynamic testing system fails to capture the volumetric strain evolution of rock under confinement. This study develops a transparent confining chamber in SHPB system with which high-speed 3D-DIC is capable of measuring both axial and circumferential strain history of dynamically compressed rock. The progressive failure stages and volumetric change of red sandstone under confining pressure of 3.5 MPa and strain rates of 129∼292 s−1 were studied and compared with those in quasi-static case. Results show that, the normalized stress thresholds of crack initiation and dilatancy in dynamic cases are much smaller than those in the quasi-static one. The volumetric variation of soft rock is characterized by four distinct stages: elastic contraction, pre-peak dilatancy, strain-softening dilatancy and strain-recovery dilatancy. The pre-peak elastic contraction is negligible compared to the post-peak dilation, and the ultimate dilation observed in dynamic compression is significantly greater than that in quasi-static compression. Increasing strain rate delays the onset of dilatancy, decreases the dilatant rate but remarkably extends the strain-softening dilatant process which is dominant in total dilation. A rate-dependent piecewise model incorporating key strain thresholds and a dilatancy rate factor was established to characterize the dynamic dilatancy behavior. The research results provide a new insight and possible method in dilation prediction for underground engineering subjected to dynamic loading.

A Scottish provenance for the Altar Stone of Stonehenge.

Understanding the provenance of megaliths used in the Neolithic stone circle at Stonehenge, southern England, gives insight into the culture and connectivity of prehistoric Britain. The source of the Altar Stone, the central recumbent sandstone megalith, has remained unknown, with recent work discounting an Anglo-Welsh Basin origin1,2. Here we present the age and chemistry of detrital zircon, apatite and rutile grains from within fragments of the Altar Stone. The detrital zircon load largely comprises Mesoproterozoic and Archaean sources, whereas rutile and apatite are dominated by a mid-Ordovician source. The ages of these grains indicate derivation from an ultimate Laurentian crystalline source region that was overprinted by Grampian (around 460 million years ago) magmatism. Detrital age comparisons to sedimentary packages throughout Britain and Ireland reveal a remarkable similarity to the Old Red Sandstone of the Orcadian Basin in northeast Scotland. Such a provenance implies that the Altar Stone, a 6 tonne shaped block, was sourced at least 750 km from its current location. The difficulty of long-distance overland transport of such massive cargo from Scotland, navigating topographic barriers, suggests that it was transported by sea. Such routing demonstrates a high level of societal organization with intra-Britain transport during the Neolithic period.

Distribution of Thanetian-Ilerdian biozones in Lorestan Zone, West of Iran

The Taleh Zang Formation is a carbonate sequence of the late Paleocene–early Eocene age in the Lorestan zone, west of Iran. This Formation overlays siliciclastic rocks of the Amiran Formation and is overlain by red sandstone of the Kashkan Formation. A biostratigraphic scheme, based on the larger benthic foraminifera, is proposed for the Thanetian–Ilerdian deposits in Lorestan Zone. We compare our results with the available data from other parts of Tethys and the zonation of shallow-marine Paleocene–Eocene of Mediterranean Tethys is made. In total, 367 samples were collected from the six sections. From a biochronostratigraphic point of view, three biozones and one indeterminate zone are identified. The zones are shallow benthic zone 3 (early Thanetian), shallow benthic zone 4 (late Thanetian), and shallow benthic zone 6 (early Ilerdian). In the northern part of the Lorestan Zone (Kabutar Bula and Psht-e Jangal sections), the Taleh Zang Formation contains poor fauna. Due to the stratigraphic position, an early Thanetian age can be considered. Our data showed that the late Paleocene and Eocene biozones in Lorestan Zone developed parallel to the axis of the folding, in a northwest-southeast trend. They get younger from the northeast to the southwest. Keywords: biostratigraphy, Eocene, Foraminifera, Lorestan Zone, Paleocene.

Influence of fissure distribution characteristics on the dynamic response of fissured Rock: Quantity and spacing

The impact test of red sandstone with different fissure distribution was carried out by Split Hopkinson Pressure Bar (SHPB). The failure process of the specimen in the time dimension was captured by high-speed camera and digital image correlation (DIC). The crushing characteristics of the specimen were discussed from the fractal dimension. Furthermore, the influence of fissure distribution characteristics (quantity and spacing of fissures) on the mechanical properties and fracture behavior of fissured red sandstone was analyzed. The experimental results show that the fissure spacing is negatively correlated with the dynamic compressive strength and peak strain of specimen, while the fissure quantity is negatively correlated with the dynamic compressive strength and positively correlated with the peak strain. Cracks are categorized into five types based on the manner of their initiation and expansion. The crack initiation and propagation are jointly affected by tensile stress and shear stress, but the tensile stress is dominant. With the increase of the fissure quantity, the failure mode changes from tensile failure to tensile-shear mixed failure. The increase of fissure spacing does not change its failure mode, but the formation mode of the main crack changes. The fractal dimension increases with the increase of the fissure quantity, and decreases with the increase of the fissure spacing, i.e., the larger the fissure quantity is, the higher the degree of fragmentation is, and the larger the fissure spacing is, the lower the degree of fragmentation is. The research results can provide a theoretical reference for the study of dynamic failure mechanism of rock mass with non-persistent discontinuities.

Strength characteristics of different stress spaces of red sandstone under loading and unloading tests

Red sandstone tests were conducted on the rock mechanics test system to clarify the strength and failure characteristics of red sandstone under triaxial loading and different unloading confining pressure rates. Strength change rules of the red sandstone in various stress spaces were analyzed. Results show that a large initial confining pressure indicates a long yield section and large axial strain. A small unloading confining pressure rate indicates a long yield section and large axial strain at failure under the identical initial confining pressure. The confining pressure reduction increases with the unloading confining pressure rate increasing when the red sandstone fails. The stress path of unloading confining pressure weakens the red sandstone cohesion and strengthens its internal friction angle. The general octahedral shear stress formula for judging whether the red sandstone fails under loading and different unloading rates was acquired on the basis of the octahedral shear stress characteristics of the red sandstone. In addition, a 3D empirical criterion for evaluating the red sandstone strength was constructed through the deviator plane function of Eekelen and the strength envelope curve on the meridian plane. A great initial confining pressure indicates serious internal damage of the red sandstone at failure under the identical unloading rate of confining pressure. A low unloading rate of confining pressure indicates internal serious damage of the red sandstone at failure when the initial confining pressure is the same. The analysis of macroscopic failure characteristics revealed that the stress path significantly influences the failure mechanism of the red sandstone. The results are instructive for determining the stability of underground engineering of the red sandstone.

Dynamic impact mechanical properties of red sandstone based on digital image correlation method

ABSTRACT In the process of underground blasting excavation, the safety and stability of rock mass are significantly influenced by dynamic load. To study the full-field strain and displacement behaviour of rock materials subjected to dynamic compressive force, the impact tests were done on red sandstone specimens using an electromagnetically driven Hopkinson pressure bar. At the same time, the data were collected by a high-speed camera, and non-contact measurements of the red sandstone were carried out with the digital image correlation method. The resulting images were screened and analysed, based on which the stress-strain curve, full-field strain cloud diagram and displacement cloud diagram were obtained. Results show that the dynamic peak stress increases with the increase of impact velocity. During the impact process, substantial internal uneven deformation occurs in the red sandstone close to the transmission bar’s end face. Under the impact load, the cracks initiate from the upper and lower sides near the transmission bar’s end face, followed by formation of cracks in the middle part. These cracks expand throughout the rock to form through-cracks, eventually resulting in complete failure. For rock materials, the evolution of their strain field during the failure process can reflect the initiation and propagation of their internal cracks. Therefore, the use of digital image correlation method proves effective for studying the deformation and failure mechanisms of rock. The conclusions obtained in this study provide a valuable reference for the macro-meso deformation and failure mechanisms of geotechnical materials.

The complete chloroplast genome of Semiaquilegia danxiashanensis (Ranunculaceae), a rare species endemic to Danxia landform in Guangdong, China

Semiaquilegia danxiashanensis is currently known only from the type locality, Danxia Mountain, characterized by its spectacular red sandstone cliffscape. In this study, we assembled the complete chloroplast genome sequence of S. danxiashanensis and inferred its phylogenetic relationships. Total length of the chloroplast genome was 160,548 bp, with an overall GC content of 39%. The chloroplast genome had typical quadripartite structure and contained one LSC region (89,882 bp) and one SSC region (17,386 bp), which were separated by two IRs regions (26,640 bp, respectively). It comprised 133 genes, including 84 protein coding genes, 41 tRNA genes and eight rRNA genes. The maximum likelihood phylogenetic analysis indicated that S. danxiashanensis was sister to S. adoxoides; meanwhile, Semiaquilegia was closely related to both Urophysa and Aquilegia in Ranunculaceae. This study sheds light on the evolutionary history of Semiaquilegia and provides preliminary data for future comparative analysis of chloroplast genomes.

Mechanical behavior and energy characteristics of red sandstone with different seawater immersion heights under biaxial compression

Rock structures engineered during undersea mining are typically subjected to varying water distributions due to the motion of seawater, which considerably influences their stability. Hence, it is essential to understand the influence of seawater distribution on the mechanical behavior and energy characteristics of rocks. In this study, biaxial compression tests were conducted on red sandstone at various seawater immersion heights, and acoustic emission signals during compression were monitored. The results illustrate that the mechanical properties of the red sandstone deteriorate significantly upon seawater immersion. With an increase in seawater immersion height, the peak strength and elastic modulus of the rock specimens decreased exponentially. When the seawater immersion height was varied from 0 to 1/4 H under lateral stresses of 5, 10, 15, and 20 MPa, the peak strength decreased by 18.94%, 20.29%, 17.47%, and 14.87%, respectively, and the elastic modulus decreased by 4.6%, 8.1%, 11.7%, and 10.9%, respectively. Brittleness also decreased gradually. During compression, the acoustic emission (AE) and accumulated AE counts exhibited a stationary phenomenon, first increasing slowly and then suddenly. However, the AE counts decrease with increasing seawater immersion height. Meanwhile, with increasing seawater immersion height, the proportion of tensile cracks gradually increased and that of shear cracks gradually decreased. As the seawater immersion height increased, both the peak total input strain energy and peak total elastic strain energy decreased, whereas the peak total dissipated strain energy exhibited the opposite trend.

Dynamic mechanical properties and fractal characteristics of red sandstone under acid corrosion

Dynamic mechanical properties and fractal characteristics of red sandstone under acid corrosion

Effect of cyclic loading level on mechanical response and microcracking behavior of saturated sandstones: Correlation with water weakening phenomenon

Rocks frequently endure water environments and diverse cyclic loading from natural and anthropogenic sources across various damage stages. Understanding the mechanical and fatigue behavior of saturated rocks under different cyclic loading levels is crucial for the intelligent design and long-term stability of the slope. Here, we report several monotonic and cyclic compression tests conducted on red and cyan sandstones under dry and water-saturated conditions, coupled with acoustic emission (AE) monitoring. We analyzed key mechanical parameters such as peak stress and peak strain, as well as AE parameters including count and energy, and dominant frequency in AE spectra. Our findings reveal that elevated cyclic loading levels significantly reduce peak stress and increase peak strain in both dry and water-saturated rocks, with more pronounced effects observed under water-saturated condition. The cumulative AE count correlates positively with increasing cyclic loading levels but decreases due to water saturation. Under cyclic loading with varying levels, dry rocks often experience shear cracking and exhibit AE waveform with high dominant frequency, while saturated rocks tend toward tensile cracking and AE waveform with low dominant frequency. Higher cyclic loading intensifies the occurrence of tensile cracking and AE waveform with low dominant frequency, which are constrained during the elastic deformation stage but become more pronounced beyond the crack initiation threshold. Moreover, cyclic loading enhances the water weakening effects in saturated rocks, closely associated with ongoing crack propagation within the rocks.