Anhydrite Rocks Research Articles

Time-Dependent Reliability Analysis of Anhydrite Rock Tunnels under Swelling Conditions: A Study on Stress, Deformation, and Engineering Solutions

This study presents an analytical approach for evaluating the reliability of anhydrite rock tunnels, focusing on their characteristic swelling behavior. Anhydrite rocks, prone to significant expansion upon moisture exposure, pose a challenge in tunnel construction, potentially leading to structural issues such as floor heave and lining damage. To address this, this research develops an elastic swelling analytical solution based on humidity stress field theory, enabling the assessment of time-dependent stress and deformation changes in anhydrite tunnels. The solution’s applicability is demonstrated through its application to the Lirang tunnel. The investigation into the effects of support pressure, swelling time, and reserved deformation on tunnel reliability reveals that circumferential stress at the tunnel wall increases by 13.94% and 21.86% for swelling periods of 30 and 365 days, respectively. Similarly, radial displacement escalates by 22.97% and 35.93% over these periods, highlighting the significant impact of swelling behavior. Using a spreadsheet-based First Order Reliability Method (FORM) for analysis, this study finds that the original design of the Lirang tunnel did not meet the desired reliability standards under swelling conditions. However, strategic adjustments in construction variables, such as increasing support pressure to 1.2 MPa or enhancing reserved deformation to 59 mm, elevated the tunnel’s reliability to meet safety requirements. This research provides a vital framework for assessing and enhancing the reliability of anhydrite rock tunnels, considering the long-term effects of swelling. It underscores the importance of incorporating swelling behavior in the design and construction of tunnels in anhydrite rock formations, offering valuable insights for optimizing tunnel stability in such challenging geological conditions.

Experimental and Numerical Research on the Tightness and Stability of Underground Anhydrite Rock Cavern Oil Storage

Experimental and Numerical Research on the Tightness and Stability of Underground Anhydrite Rock Cavern Oil Storage

Experimental and Numerical Simulation Investigation of the Mechanical Properties of Anhydrite Rock Under Freeze–Thaw Environment

Experimental and Numerical Simulation Investigation of the Mechanical Properties of Anhydrite Rock Under Freeze–Thaw Environment

A Practical Swelling Constitutive Model of Anhydrite and Its Application on Tunnel Engineering

Swelling of anhydrite rock causes serious damage to the tunnel and generates high additional costs in the process of tunnel construction and operation and has gradually become one of the main factors that threaten the safety of the tunnel. It is extremely difficult to predict swelling pressures and deformations accurately based on conventional swelling constitutive models. Thus, a new practical swelling constitutive model of anhydrite for tunnel engineering has been developed. First, swelling tests of natural anhydrite samples focusing on the time effect have been designed and conducted, whose test results show that swelling strain-time can be described by the S-curve model and that swelling stress-strain can be described by the quadratic model. Second, a swelling constitutive model with considering the time effect has been developed to reproduce the swelling behavior of anhydrite observed in swelling tests. This model can track the evolution of swelling activity in tunneling, which has practical significance for process simulation and process control of swelling disaster. Then, this model has been implemented within ANSYS for numerical simulation of the Lirang tunnel. Based on simulation results, useful measures have been proposed. Satisfactory results have been achieved according to the feedback from the site.

Investigation of the Multi-Scale Deterioration Mechanisms of Anhydrite Rock Exposed to Freeze-Thaw Environment.

The deterioration of anhydrite rock exposed to a freeze-thaw environment is a complex process. Therefore, this paper systematically investigated the physical and mechanical evolutions of freeze-thawed anhydrite rock through a series of multi-scale laboratory tests. Meanwhile, the correlation between pore structure and macroscopic mechanical parameters was discussed, and the deterioration mechanisms of anhydrite rock under freeze-thaw cycles were revealed. The results show that with the increase in freeze-thaw processes, the mechanical strength, elastic modulus, cohesion, proportions of micropores (r ≤ 0.1 μm), and PT-Ipore throat (0-0.1 μm) decrease exponentially. In comparison, the mass variation, proportions of mesopores (0.1 μm < r < 1 μm), macropores (r ≥ 1 μm), and PT-II pore throat (0.1-4 μm) increase exponentially. After 120 cycles, the mean porosity increases by 66.27%, and there is a significant honeycomb and pitted surface phenomenon. Meanwhile, as the freeze-thaw cycles increase, the frost resistance coefficient decreases, while the damage variable increases. The correlation analysis between pore structure and macroscopic mechanical parameters shows that macropores play the most significant role in the mechanical characteristic deterioration of freeze-thawed anhydrite rock. Finally, it is revealed that the water-rock expansion and water dissolution effects play a crucial role in the multi-scale damage of anhydrite rock under the freeze-thaw environment.

Rapid hydration and weakening of anhydrite under stress: implications for natural hydration in the Earth's crust and mantle

Abstract. Mineral hydration is an important geological process that influences the rheology and geochemistry of rocks and the fluid budget of the Earth's crust and mantle. Constant-stress differential compaction (CSDC) tests, dry and “wet” tests under confining pressure, and axial-stress tests were conducted for the first time to investigate the influence of triaxial stress on hydration in anhydrite–gypsum aggregates. Characterization of the samples before and after triaxial experiments was performed with optical and scanning electron microscopy, including energy-dispersive spectroscopy and electron backscatter diffraction mapping. Stress–strain data reveal that samples that underwent constant-stress differential compaction in the presence of fluids are ∼ 14 % to ∼ 41 % weaker than samples deformed under wet conditions. The microstructural analysis shows that there is a strong temporal and spatial connection between the geometry, distribution, and evolution of fractures and hydration products. The increasing reaction surface area in combination with pre-existing gypsum in a gypsum-bearing anhydrite rock led to rapid gypsification. The crystallographic orientations of newly formed vein gypsum have a systematic preferred orientation for long distances along veins, beyond the grain boundaries of wall-rock anhydrite. Gypsum crystallographic orientations in {100} and {010} are systematically and preferentially aligned parallel to the direction of maximum shear stress (45∘ to σ1). Gypsum is also not always topotactically linked to the wall-rock anhydrite in the immediate vicinity. This study proposes that the selective inheritance of crystal orientations from favourably oriented wall-rock anhydrite grains for the minimization of free energy for nucleation under stress leads to the systematic preferred orientation of large, new gypsum grains. A sequence is suggested for hydration under stress that requires the development of fractures accompanied by localized hydration. Hydration along fractures with a range of apertures up to 120 µm occurred in under 6 h. Once formed, gypsum-filled veins represent weak surfaces and are the locations of further shear fracturing, brecciation, and eventual brittle failure. These findings imply that non-hydrostatic stress has a significant influence on hydration rates and subsequent mechanical strength of rocks. This phenomenon is applicable across a wide range of geological environments in the Earth's crust and upper mantle.

Host-rock and caprock wettability during hydrogen drainage: Implications of hydrogen subsurface storage

Underground hydrogen storage (UHS) is an integral part of H2 economy value chain, essential for industrial-scale actualization of global decarbonization objectives. UHS in depleted hydrocarbon reservoirs is considered a safer and promising storage technique due to presence of large porous formation and impermeable seal, but its effectiveness depends on precise estimation of rock wettability, a crucial parameter in reservoir characterization, which controls pore-scale gas distribution, H2 containment safety and withdrawal efficiency. Several recent studies have provided contact angles data for host rock-water-H2 (quartz and sandstone) and caprock-water-H2 (mica and shale) measured through sessile drop method. However, the contact angle datasets for carbonate rock-water-H2 measured via captive bubble method, which can reflect the wettability of the rock during imbibition and drainage are largely unknown. The present work characterized the wettability of carbonate-water-H2 systems for various rock types, prepared from five different lithologies with different mineral assemblages. The contact angle θ was measured using the captive bubble method at two different temperatures of 303 K and 348 K, and three different pressures (3.44, 10.34, and 17.23 MPa). Experimental results showed that all rocks remained intrinsically strongly water-wet (θ ranged between 17° – 30°) at all experimental conditions. Furthermore, no significant change in contact angles occurred with changing temperature and pressure. For instance, at 17.23 MPa, contact angle of H2/brine on anhydrite (S-4) rock were measured as 19° and 20° at 303 K and 348 K respectively, suggesting that H2 remains the non-wetting phase with increasing storage depth and at warmer reservoirs. The study suggests that the pore-scale flow and fluid connectivity of H2 may not be influenced by changing wettability in pure storage rocks/caprocks. Thus, the wettability of carbonates storage rocks and caprocks may not be over-predicted by assuming strongly water-wet conditions for the non-contaminated rock surfaces during UHS.

Hydration caves and cavities from the recent weathering zone of anhydrites at Dingwall (Nova Scotia, Canada)

Hydration of anhydrite to gypsum (gypsification of anhydrite) in the weathering zone sometimes causes a volume increase. This can lead to local detachments of the surface layer of the weathering anhydrite rocks and creation of the hydration cavities and rare hydration caves (or swelling caves; German: Quellungshöhlen) inside domes formed by the uplifted layer. Currently growing hydration cavities at the anhydrite bottom of the abandoned quarry at Dingwall, Canada, were studied with the use of photogrammetric, statistic, and petrographic methods. Seventy seven cavities were documented including 48 caves (cavities with the height ≥0.30 m large enough to accommodate an adult man). Forty three caves had proper entrances (inlets large enough for an adult to get inside). The cavities contain one flat domed or, less often, tepee-like chamber generally similar in shape to the host hydration landform. The majority of cavities showed the length <4.6 m, the width <3.0 m, and the height <0.85 m. Only 3 caves had the length >8.00 m and the height ≥0.80 m. The largest and the highest cave showed the sizes 10.7 × 6.6 × 1.1 m measured in 2008 which changed into 8.87 × 2.97 × 1.35 m in 2019. The other caves and cavities exhibit also morphological changes with time due to vertical and horizontal movements of rocks slabs and collapse of the roofs depending mainly on the location of expansive gypsification and its intensity. Precipitation (rain- and meltwater) accumulating at the foot of the initial uplift intensifies the hydration in this zone causing a centripetal pressure towards the landform and contributing to its further rising and enlargement of the cavity height. The basic condition required for hydration cave formation is temperature between 0 and 30 °C in which the solubility of gypsum is much lower than that of anhydrite. The meteoric water solution infiltrating in the vadose zone is dissolving the anhydrite and gradually reaches Ca sulphate concentration higher than the level of gypsum and lower than the level of anhydrite solubility. Then, the dissolving anhydrite yields a solution supersaturated with gypsum, capable of its precipitation, and the dissolution of anhydrite is simultaneous with in situ replacive/displacive gypsum crystallization. The crystallization pressure of gypsum is a direct cause of the rock deformations and creation of hydration caves.

Mechanical and acoustic emission characteristics of anhydrite rock under freeze-thaw cycles

Mechanical and acoustic emission characteristics of anhydrite rock under freeze-thaw cycles

Erratum for “Statistical Damage Constitutive Model for Anhydrite Rock under Freeze–Thaw Cycles Considering the Residual Strength and Postpeak Stress Dropping Rate” by Chao Hou, Xiaoguang Jin, Jie He, and Hanlin Li

Erratum for “Statistical Damage Constitutive Model for Anhydrite Rock under Freeze–Thaw Cycles Considering the Residual Strength and Postpeak Stress Dropping Rate” by Chao Hou, Xiaoguang Jin, Jie He, and Hanlin Li

Statistical Damage Constitutive Model for Anhydrite Rock under Freeze–Thaw Cycles Considering the Residual Strength and Postpeak Stress Dropping Rate

Statistical Damage Constitutive Model for Anhydrite Rock under Freeze–Thaw Cycles Considering the Residual Strength and Postpeak Stress Dropping Rate

Experimental studies on the pore structure and mechanical properties of anhydrite rock under freeze-thaw cycles

To study the deterioration mechanisms of anhydrite rock under the freeze-thaw weathering process, the physico-mechanical characteristics and microstructure evolutions of anhydrite samples were determined by a series of laboratory tests. Then, a descriptive-behavioral model was used to measure the integrity loss in anhydrite samples caused by cyclic freeze-thaw. Finally, the freeze-thaw damage mechanisms of anhydrite rock were revealed from the macro and micro aspects. The results show that the pore size of the anhydrite rock is mainly concentrated in the range of 0.001–10 μm. As the number of freeze-thaw cycles increases, there is a growth in the proportion of macropores and mesopores. However, the proportion of micropores shows a declining trend. The relations of the uniaxial compressive strength, triaxial compressive strength, cohesion, and elastic modulus versus freeze-thaw cycles can be fitted by a decreasing exponential function, while the internal friction angle is basically unchanged with freeze-thaw cycles. With the increase of confining pressure, the disintegration rates of the compressive strength and the elastic modulus decrease, and the corresponding half-life values increase, which reveals that the increase of confining pressures could inhibit freeze-thaw damage to rocks. Moreover, it has been proven that the water chemical softening mechanism plays an essential role in the freeze-thaw damage to anhydrite rock. Furtherly, it is concluded that the freeze-thaw weathering process significantly influences the macroscopic and microscopic damages of anhydrite rock.

Tightness Analysis of Anhydrite Mine-Out Used for Underground Crude Oil Storage Considering Seepage–Stress Coupling: A Case Study

Good tightness is one of the necessary conditions for an anhydrite mine-out space to be used for underground crude oil storage. Combining engineering geological surveys, laboratory tests, and numerical simulations, this paper quantitatively analyses the tightness of the Anhui Hengtai anhydrite mine-out under different working conditions and discusses its suitability for underground crude oil storage. Triaxial compression tests of anhydrite rock considering seepage were carried out to study its hydraulic and mechanical characteristics during failure. The permeability coefficient–strain empirical formula of anhydrite was constructed. A numerical simulation was carried out on the basis of the finite difference method to study the tightness of the rock surrounding the mine-out after excavation and under 0.2 MPa, 0.6 MPa, and 1.0 MPa storage pressures, respectively. The results showed that the permeability coefficient increased with increasing storage pressure, and the growth rate gradually slowed after the storage pressure reached a certain value. Overall, the mine-out had good tightness, and the permeability coefficient of the surrounding rock was small. This study demonstrated the feasibility of using the anhydrite mine-out for crude oil storage and provides a scientific basis for the site selection of underground crude oil storage.

Investigation on the Microscopic Deterioration Characteristics of Anhydrite Rock Exposed to Freeze–Thaw Cycles

Investigation on the Microscopic Deterioration Characteristics of Anhydrite Rock Exposed to Freeze–Thaw Cycles

Petrographic Record and Conditions of Expansive Hydration of Anhydrite in the Recent Weathering Zone at the Abandoned Dingwall Gypsum Quarry, Nova Scotia, Canada

In the Dingwall gypsum quarry in Nova Scotia, Canada, operating in 1933–1955, the bedrock anhydrite deposits of the Carboniferous Windsor Group have been uncovered from beneath the secondary gypsum beds of the extracted raw material. The anhydrite has been subjected to weathering undergoing hydration (gypsification), transforming into secondary gypsum due to contact with water of meteoric derivation. The ongoing gypsification is associated with a volume increase and deformation of the quarry bottom. The surface layer of the rocks is locally split from the substrate and raised, forming spectacular hydration relief. It shows numerous domes, ridges and tepee structures with empty internal chambers, some of which represent unique hydration caves (swelling caves, Quellungshöhlen). The petrographic structure of the weathering zone has been revealed by macro- and microscopic observations. It was recognized that gypsification commonly starts from a developing network of tiny fractures penetrating massive anhydrite. The gypsification advances from the fractures towards the interior of the anhydrite rocks, which are subdivided into blocks or nodules similar to corestones. Characteristic zones can be recognized at the contact of the anhydrite and the secondary gypsum: (1) massive and/or microporous anhydrite, (2) anhydrite penetrated by tiny gypsum veinlets separating the disturbed crystals and their fragments (commonly along cleavage planes), (3) gypsum with scattered anhydrite relics, and (4) secondary gypsum. The secondary gypsum crystals grow both by replacement and displacement, and also as cement. Displacive growth, evidenced by abundant deformation of the fragmented anhydrite crystals, is the direct cause of the volume increase. Crystallization pressure exerted by gypsum growth is thought to be the main factor generating volume increase and, consequently, also the formation of new fractures allowing water access to “fresh” massive anhydrite and thus accelerating its further hydration. The expansive hydration is taking place within temperature range from 0 to ~30 °C in which the solubility of gypsum is lower than that of anhydrite. In such conditions, dissolving anhydrite yields a solution supersaturated with gypsum and the dissolution of anhydrite is simultaneous with in situ replacive gypsum crystallization. Accompanying displacive growth leads to volume increase in the poorly confined environment of the weathering zone that is susceptible to upward expansion.

Impact of Hydrodynamic and Interfacial Interactions on Scale Formation in a Capillary Microchannel.

This study proposes a model for the kinetics and hydrodynamics of gypsum scale deposition on surfaces of anhydrite, calcite, dolomite, and sandstone rocks while interacting with the brines of 3000 and 6000 mg/L [Ca2+] at 363 K and 1 atm. To do so, this study utilizes the surface energy characteristics of an interacting scale-brine-rock system as well as the geochemical interactions between brine-brine and brine-rock. The results showed that the deposition flux decreases steeply over time, followed by asymptotic propensity as time elapses. A higher degree of salinity in terms of [Ca2+] increases the deposition flux as much as 2.9-fold for the flowing velocity of 10-6 m/s and 2.4-fold for a velocity of 10-5 m/s. Moreover, higher flow velocity would lead to more deposition on sandstone followed by carbonate and anhydrite rocks: ∼2.6-fold for the salinity of 3000 mg/L and 2.2-fold for 6000 mg/L [Ca2+].

Density - Velocity Relationship and Prediction of Lithology Variation Using Physical Analysis in Kf-4 Well of The Kifl Oil Field, Yamama Formation, South of Iraq

The density-velocity relation is an important tool used to predict one of these two parameters from the other. A new empirical density –velocity equation was derived in Kf-4 well at Kifl Oil Field, south of Iraq. The density was derived from Gardner equation and the results obtained were compared with the density log (ROHB) in Kl-4 well. The petrophysical analysis was used to predict the variations in lithology of Yamama Formation depending on the well logs data, such as density, gamma, and neutron logs. The physical analysis of rocks depended on the density, Vp, and Vs values to estimate the elastic parameters, i.e. acoustic impedance (AI) and Vp/Vs ratio, to predict the lithology and hydrocarbon indicators. According to the results of physical properties, Yamama Formation is divided into five units in Kf-4 well at Kifl Oil Field. The lithology of Yamama Formation was found to consist of limestone, dolomite, shale, and anhydrite rocks.

Correlation between the mineral composition and strength properties of sulfate rocks

A literature review confirms that the effect of mineral composition on the strength properties of rocks has rarely been studied. One of the most problematic sedimentary rock types is sulfate rocks, which cause engineering problems in infrastructure sites such as reservoir dams. In this paper, for the first time, the effect of mineral composition on the strength properties of sulfate rocks was investigated. Rock blocks were collected from Gachsaran Formation outcrops at four reservoir dam sites under construction in Iran. After preparation, drying and saturation of the rock core samples (329 samples), uniaxial compressive strength tests were performed in accordance with ASTM and ISRM standards. The results of this study confirmed the following: (1) there is a correlation between the mineral composition and the strength properties of the sulfate rocks but the obtained relationships do not have the necessary certainty to be used as predictive equations; (2) by increasing the amount of anhydrite or microcrystalline carbonates in a gypsum rock, its strength properties are improved; (3) in a dry condition the dominant failure mode in gypsum and anhydrite rocks is a shear and dilatation mode, respectively, but after saturation, the failure mode tends to be a shear mode.

Verification of Gardner's equation and derivation of an empirical equation for anhydrite rocks in Sirte basin, Libya: case study

Bulk density is a physical property of rocks measured in the laboratory on rock samples or obtained from oil field logging tools. When bulk density is not measured, a synthetic bulk density log can be calculated, for which Gardner's equation is the most widely used. However, Gardner's equation might not be appropriate for regions in which the density–velocity relationship does not conform to Gardner's curves. Here, we verified the applicability of Gardner's equation to calculation of synthetic bulk density of anhydrite rocks in the Sirte Basin (Libya) and compared the results to those obtained from an equation derived from the available measured bulk density and sonic logs. We used fifteen wells to calibrate Gardner's equation and three wells to derive an equation for the anhydrite rocks. The anhydrite rocks were 10–510 feet thick. The bulk density calculated by Gardner's equation differed only slightly from the measured log values, with the exception of the eastern part of the Sirte Basin. The average of the differences in bulk density between the measured values and Gardner's equation results were 0.022–0.040 g/cm3, and between the measured values and the derived equation results 0.002–0.045 g/cm3, both with a standard error of about 0.01 of the bulk density estimated results. We conclude that while Gardner's equation is more appropriate for estimating the bulk density of anhydrite rocks in the eastern part of the basin, the derived equation could be more appropriate for the western region.

Finite element analysis of embankments on gypsiferous subgrade soil - stone column strengthened with geogrid

Gypsum and anhydrite rocks are frequently found in numerous countries of the world in extensive deposits, the huge region in middle and west of Iraq is classified as a gypseous soil. Stone columns are non-time dependent foundation technique used to increase the structural stability and to reduce the structural deformations of soil. In the present study, the finite element method is used as a tool to utilized the effect of using stone columns with geogrid as reinforcing material for treatment gypsiferous subgrade soil under embankment during both construction and consolidation conditions. The results show that decreasing the stone column spacing leads to a considerable decrease in the settlement beneath the embankment, especially below the center line, reduction in the settlement of about 60% and when using geosynthetic material the reduction about 75%. Also, increases the excess pore water pressure immediately after the construction of each lift of the embankment and then falls with and without using geosynthetic material. The vertical stress in the gypsiferous subgrade soil increases at a very small rate especially in the early stages and decreases as stone columns spacing decreases.