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The failure and deformation mechanism of sandstone and mudstone has always been highlighted in research on mining engineering. To further investigate the failure and deformation mechanism of sandstone and mudstone, a damage definition was proposed to describe the failure mechanism of a rock specimen with micro-defects and inhomogeneity; the Weibull distribution function was used to illustrate the dispersion of mechanical properties (i.e. damage extent) of rock; the nonconstant terms of Z–P yield function was employed to describe the strength of rock elements. Based on the framework of the continuum damage mechanics and strain equivalence hypothesis, a continuous damage constitutive model was established. Finally, triaxial compression tests on sandstone and mudstone taken from the Chensilou coal mine were conducted to verify the reliability of the proposed model. The results show that the damage evolution curve presents the shape of a square root sign, The damage evolution of the rock specimens can be divided into six stages: (1) initial damage stage, (2) damage-weakening stage, (3) slight-increased damage stage, (4) rapidly-increased damage stage, (5) rock failure stage and (6) rock slippage stage. The proposed damage evolution contributes to establishing the constitutive model of the stress–strain relationship of sandstone and mudstone in the mining field.HighlightsProcessing a continuous damage statistical constitutive model for sandstone and mudstone based on triaxial compression tests.The damage evolution curve presents the shape of a square root sign.The damage evolution of the rock: initial damage-damage weakening-slight increased-rapidly increased-rock failure-rock slippage.

Identified phases and their distributions in each region of the samples studied. https://doi.org/10.1371/journal.pone.0195421.t001 The second sentence of the fourth paragraph in the \"Preservation of the rib bone matrix\" section of the Discussion should have cited Fig 8 instead of Fig 7. Based on Fig 8, cross-FIB-milled samples from bone matrix areas rich in illite show higher degrees of preferred apatite orientation, suggesting that illite may have taken a direct role in preserving the structural integrity of the bone. 1.

Water has a significant effect on the mechanical properties of rocks, especially those containing expansive clay minerals. The red-layer mudstone contains various clay minerals, which easily collapse in water. To further study the effect of water on the mechanical properties of red-layer mudstone, uniaxial and triaxial tests were first conducted on samples with different moisture contents, prepared using the gaseous moisture absorption method in the laboratory. The effect of water on the fracture mode, mechanical behaviour and strength of the red-layer mudstone was subsequently studied at a heterogeneous particle scale using the three-dimensional numerical simulation program 3DEC. The results demonstrated that the strengths of the mudstone samples (uniaxial compressive and triaxial compressive strengths) decreased with an increase in the moisture content. As the moisture content increased, the elastic modulus and residual strength of mudstone decreased. The Mohr–Coulomb strength envelope under different moisture contents was constructed, and it was found that with an increase in the moisture content, the cohesion of the mudstone decreased significantly and the internal friction angle remained almost unchanged. This numerical model accurately demonstrates the damage evolution (tensile and shear cracks) at a heterogeneous particle scale. Simultaneously, the macroscopic mechanical behaviour, strength and failure patterns observed in the laboratory were reproduced. Finally, this study reveals the weakening mechanism of water on the mechanical properties of red-layer mudstone at macroscopic and Ümesoscopic scales.HighlightsNumerical simulation and laboratory tests were used to study the variation of mechanical properties of red-layer mudstone with moisture contents and the weakening mechanism of moisture on its mechanical propertiesMudstone samples with different moisture contents were prepared by gaseous hygroscopic method, which overcame the challenge of mudstone disintegrating in waterThe discrete element method (3DEC) was used to randomly generate heterogeneous mudstone samples with different clay mineral grains.An empirical formula was established to predict the mechanical properties of red-layer mudstones at different moisture content.The effects of different moisture contents on mesoscopic mechanical parameters and joint displacements of contacts between red-layer mudstone grains were analysed.

In the Triassic Mercia Mudstone Group of the Bristol Channel area, SW Britain, yellow micritic-oolitic dolomites deposited in a near-shore location of an extensive shallow saline alkaline lake, pass landwards into conglomerates and sandstones of colluvial-fluvial origin (Dolomitic Conglomerate). Offshore facies are red marl (Branscombe Fm.) and grey-green marl (Blue Anchor Fm.) of shallow lake-playa origin. Conspicuous red silicified bands and nodules (cherts) occur within the shoreline dolomites cropping out at Clevedon, 30 km SW of Bristol. The originally aragonitic ooids and lime mud were dolomitized very early on the lake floor and just below, and the presence of pyrite indicates anoxic conditions therein. The silicification is attributed to the influx of meteoric water with near-neutral pH, provided by flash floods and rainstorms as hyperpycnal and hypopycnal flows, interacting with the silica-rich, saline, alkaline lake water and porewater within the lake sediment. Aragonitic ooids picked up in the flows underwent dissolution, then slight compaction of outer dolomitic lamellae, before silica precipitation. The red colour of the chert from detrital finely disseminated hematite also indicates very early precipitation, before suboxic-anoxic conditions developed in the enclosing lake carbonates. These Triassic sediments show features of soft-sediment deformation, attributed to the formation of chert via a silica gel and/or density contrasts of rapid deposition-dewatering, plus possible seismic activity connected to a nearby basin-margin fault.

Global perturbations to the Early Jurassic environment (∼201 to ∼174 Ma), notably during the Triassic–Jurassic transition and Toarcian Oceanic Anoxic Event, are well studied and largely associated with volcanogenic greenhouse gas emissions released by large igneous provinces. The long-term secular evolution, timing, and pacing of changes in the Early Jurassic carbon cycle that provide context for these events are thus far poorly understood due to a lack of continuous high-resolution δ13C data. Here we present a δ13CTOC record for the uppermost Rhaetian (Triassic) to Pliensbachian (Lower Jurassic), derived from a calcareous mudstone succession of the exceptionally expanded Llanbedr (Mochras Farm) borehole, Cardigan Bay Basin, Wales, United Kingdom. Combined with existing δ13CTOC data from the Toarcian, the compilation covers the entire Lower Jurassic. The dataset reproduces large-amplitude δ13CTOC excursions (>3‰) recognized elsewhere, at the Sinemurian–Pliensbachian transition and in the lower Toarcian serpentinum zone, as well as several previously identified medium-amplitude (∼0.5 to 2‰) shifts in the Hettangian to Pliensbachian interval. In addition, multiple hitherto undiscovered isotope shifts of comparable amplitude and stratigraphic extent are recorded, demonstrating that those similar features described earlier from stratigraphically more limited sections are nonunique in a long-term context. These shifts are identified as long-eccentricity (∼405-ky) orbital cycles. Orbital tuning of the δ13CTOC record provides the basis for an astrochronological duration estimate for the Pliensbachian and Sinemurian, giving implications for the duration of the Hettangian Stage. Overall the chemostratigraphy illustrates particular sensitivity of the marine carbon cycle to long-eccentricity orbital forcing.

To identify the mechanisms that caused landslides during the construction of the Jilin-Hunchun high-speed railway line in Yanji, China, the engineering properties of weathered swelling mudstones extracted from a representative landslide site were investigated. The experimental results indicate that both yellow-brown and magenta mudstones exhibit significant swelling and shrinkage behaviour due to significant amounts of swelling clay minerals. The yellow-brown mudstone has an obvious schistose structure with stacked flaky plates interconnected with a face-to-face pattern, while the magenta mudstone has an aggregated structure cemented by iron oxides. Both mudstones are prone to disintegration when soaked in water. The shear strengths of swollen samples decrease dramatically compared with those of unsaturated samples, and the lower the initial water content is, the smaller the shear strength of a sample after swelling. By repeatedly increasing the repeated drying-wetting-freezing-thawing cycles, the shear strength decreases. According to the experimental findings, the effects of the engineering properties of mudstones on the landslides occurrence in the Yanji section are discussed. Heavy rainfall and the weathering of mudstones induced by fluctuating climatic conditions are regarded as the principal factors that triggered the landslides. Given the high landslide incidence on south-facing slopes, the influence of slope orientation on the stability of mudstone slopes is studied and discussed.

Expansive surrounding rock, such as mudstone, poses significant risks to supporting structures like tunnel linings due to its tendency to expand. To explore the expansion mechanism of expansive surrounding rock and address underground engineering challenges associated with it, this study, based on the first phase of Guiyang Metro Line S1, samples expansive surrounding rock from the section and conducts basic physical tests, X-ray diffraction (XRD), and scanning electron microscopy (SEM) analyses on the samples. The influence of water content (0%, 2.93%, 6.84%, and 8.20%) on the mechanical properties of mudstone, as well as its expansion characteristics under natural conditions, were examined. Results indicate that the microscopic surface of mudstone is rough, with cracks distributed around pores. These elements interconnect to form natural water channels, with clay minerals and non-clay minerals comprising 47.2% and 52.8% of the sample, respectively. Mudstone contains multiple pores that gradually develop as water content increases. Mudstone expansion significantly reduces its compressive strength. When lateral constraints are applied, mudstone exhibits significantly greater expansion compared to axial and radial changes. When mudstone encounters water, the expansion pressure fluctuates significantly. Upon water absorption following dehydration, cracks in the rock sample develop rapidly, accelerating collapse. These findings offer valuable insights for the construction and design of tunnels in expansive surrounding rock formations within karst areas.

The influence of water on rock deformation and failure behavior is a critical variable to consider when developing unconventional shale reservoirs. To better understand this effect, we conducted a series of triaxial compression tests on four mudstone lithofacies, namely siliceous calcareous mudstones, siliceous mudstones, calcareous mudstones, and carbonate-rich mudstones from the Naparima Hill Formation, under water-saturated conditions at confining pressures up to 130 MPa. Our results showed that the mudstones displayed brittle, brittle–ductile transition, and ductile failure behaviors as the confining pressure increased. Mudstones with low strength, high porosity, and high silica and clay contents exhibited a strong water-weakening effect, leading to a significant reduction in failure strength. Conversely, high strength, low porosity, and carbonate-rich mudstones showed minor water-weakening effects. We also developed a failure behavior model to predict the brittle, brittle–ductile transition, and ductile zones in the mudstones. The model showed that the transition from brittle to ductile behavior occurs over a wide range of confining pressures, and it occurs at a lower pressure threshold in saturated compared to dry conditions. Additionally, the model suggests that the presence of water results in a wider transition zone between brittle and ductile behavior, as well as a larger ductile zone. Overall, our findings suggest that the water-weakening effect can significantly decrease the depth at which the brittle–ductile transition occurs in mudstones, emphasizing the importance of considering water as a critical variable in rock deformation and failure behavior.HighlightsTriaxial compression test was conducted on mudstone specimens to investigate the impact of water content on failure behavior.An experimental model that predicts the brittle, brittle–ductile transition, and ductile failure behavior is developed for water-saturated mudstones.Low-strength, high-porosity mudstones with high levels of silica and clay are significantly weakened in the presence of water.Brittle–ductile transition behavior is influenced by the strength, porosity, and mineralogy of the mudstones.Brittle–ductile transition occurred over a wide range of confining pressures, with a lower threshold in saturated than dry conditions.

We explore${\\rm CO}_2$injection into a layered permeable rock consisting of high permeability reservoir layers, separated by low permeability mudstone, and taking the shape of an anticline within a laterally extensive aquifer. We first show how the storage capacity of the formation depends on the capillary entry pressure of the inter-layer mudstone, so that${\\rm CO}_2$cannot flow from one layer into the next. We then consider a formation composed of two layers, overlain by a cap rock. For injection into the lowest layer, we show that the injection rate, capillary entry pressure and buoyancy driven flux through the mudstone determine whether the lower or upper layer fills to the spill point first. We also show that at the end of the injection phase,${\\rm CO}_2$may continue to flow from the lower to the upper layer. This implies that injection should be stopped once the injected volume matches the static capacity of the formation in order to prevent spilling after injection. We present a series of analogue experiments of a two layered system that illustrate some of the principles described by the model, and assess the implications of the results for field scale systems.

Interactions between organic matter (OM) and clay minerals have received considerable attention in previous studies. The influence of OM on smectite illitization has been analyzed primarily in simulation experiments rather than in diagenetic studies. The present study explores the influence of OM on smectite illitization during diagenesis. Thirty red and dark mudstone samples from the Dongying Depression were analyzed. X-ray diffraction (XRD) analyses revealed that the illite percentages in mixed-layer illite-smectite (I-S) of both types of samples were dispersive above 3100 m and more convergent below this depth. The stacking mode of I-S in dark mudstones above 3100 m remained primarily at R0-R0.5 ordering with the average number of layers (Nave) dispersively distributed between 2 and 4.5. In red mudstones, the I-S changed from the R0 to R0.5 mode with the Nave increasing from 2 to 5. Over this range, the smectite illitization in dark mudstones was slower than that in red mudstones. Below 3100 m, the I-S stacking mode of dark mudstones changed from R0.5 to R3 ordering with the Nave increasing sharply from 4 to 8. In red mudstones, the I-S displayed R1.5 and R3 ordering with the Nave varying between 4.5 and 6.5. Over this range, the smectite illitization in dark mudstones accelerated rapidly, whereas the process in red mudstones was retarded. Additionally, the red mudstone samples contained little OM, whereas the dark mudstone samples contained abundant total organic carbon (0.17-4.43%). Thermo-XRD, near-infrared (NIR) as well as mid-infrared (MIR) spectroscopy analyses suggested that the OM in dark mudstones exhibited a significant transition at 3100 m, coincident with the illitization change. Above 3100 m, the smectite illitization in dark mudstones was delayed due to the OM pillar effect in the interlayer spaces of smectite. Below 3100 m, the interlayer OM became varied and desorbed, discharging organic acid. This led to the dissolution of smectite structural layers. Consequently, illitization in the dark mudstone was accelerated. This study revealed that the existence and occurrence of OM could influence the smectite illitization in diagenesis. Further study on the interactions between OM and clay minerals is needed to facilitate our understanding on the mechanism of smectite illitization as well as its geological applications.