Overburden Pressure Research Articles

The Effects of Pressure on Lithium Alloying/Dealloying

Stack pressure and mechanical confinement play important roles in influencing electro-chemo-mechanical phenomena of active materials in batteries, fuel cells, electrolyzers, and other energy conversion/storage devices. Despite progress in engineering strategies that aim to achieve stable stress/strain evolution and durable device performance, our mechanistic understanding of the coupling between mechanics and electrochemistry that govern structural evolution and electrochemical behavior of electrodes remains limited. Here, we investigate the effects of stack pressure on electrochemical lithium (de)alloying using both liquid and solid-state electrolytes. We elucidate the role of stack pressure on morphological evolution and electrochemical behavior of various alloy anodes in lithium batteries. Based on the understanding gained herein, we design an interfacial layer for alloy anodes in solid-state batteries to achieve high capacity and stable cycling at low stack pressures. These results provide insight into the phase transformation mechanism of metals and alloys under mechanical confinement, and they have implications for the development of high-energy solid-state battery systems.

Accurate Analysis of Stand-up Time Rock Collapse When Inlet Tunnel Excavation is Carried out in there are Cracked and Broken Rock Formations and a Poorly Silty-clay Soil Profile

The condition of the rock formation and the poor stability of the type of soil mass (problematic soil) in the tunnel excavation route greatly influence the achievement of the collapse (stand-up time) that will occur. The thickness of the overburden pressure above the tunnel opening is often difficult to meet, so in the inlet zone as well as in the out-let zone, slope collapse often occurs and disrupts the work implementation schedule. On the slope of the inlet excavation location, there are also silt formations with outcroppings. Rocks from small to large sizes and there are even rock masses that are cracked so that the quality or strength of the rock is unstable when exposed to the equipment used when tunnel excavation work is carried out. This research method was carried out using an approach that corresponds to the Rock Quality Designation (RQD) value with the Rock Mass Rating (RMR) value which will provide a classification of rock classes and excavation methods. The data used in this research is rock data at the tunnel inlet of the Rukoh Dam Steering Building. From the RQD and RMR data and soil physical properties obtained in this research, analysis was carried out using the empirical approach introduced by Bieniawski. The results obtained from the in-situ test drilling work, the results of which were stored in the core box at the tunnel inlet, obtained an RQD value equal to 32.5% and an RMR value equal to 15. The RMR value shows that the rock at the tunnel inlet falls into the very category poor. With a tunnel opening as wide as 6.60 M, the stand-up time at the tunnel in-let is less than 30 minutes.

Study on the Mechanical Parameters and Permeability of Coal Reservoirs at Different Temperatures.

Deep coal reservoirs, as opposed to their shallower counterparts, exhibit characteristics of higher temperatures and pressures. These conditions affect the fracture structure and mechanical properties of coal, which in turn controls permeability. Substantial studies have been conducted to determine the effects of overburden pressure on permeability, but the correlation between the temperature and mechanical parameters/permeability of coal remains unclear. This study focused on low-rank bituminous coal from the southern edge of the Junggar Basin in Xinjiang. Using experiments conducted on seepage and mechanics at different depths (considering effective stress and temperature), the study investigated how temperature affects the mechanical parameters and permeability of coal column samples. A permeability prediction model was established incorporating temperature, mechanical parameters, and effective stress. The results show that from 20 to 80 °C, the elastic modulus of coal column samples decreases by 31.0%, and the Poisson ratio increases by 72.0%. Permeability decreases between 48.37 and 90.12% under different depths. The stress sensitivity coefficient under various temperature conditions decreased exponentially as the effective stress increased, and the temperature sensitivity coefficient under various effective stress conditions decreased with increasing temperature. The permeability was more sensitive to a temperature below 40 °C. In the permeability prediction model, the fracture compressibility coefficient is bifurcated into two coefficients, each controlled by temperature and effective stress. The permeability prediction error of the model was 12.7% under constant effective stress and 17.2% under varying effective stress and temperature conditions. The study could provide guidance for fracturing and coalbed methane production in deep coal reservoirs.

Study on shale hydrocarbon generation pressurization and its influencing factors - taking Guoyuan area of Ordos Basin as an example

The increase in shale hydrocarbon production is the main driver of crude oil accumulation, but the lack of effective theoretical and technical means limits exploration and development. In this study, the quantitative calculation method of hydrocarbon generation pressurization was improved by the hydrocarbon overburden pressure simulation experiment. The relationship between the rate of hydrocarbon conversion rate and the content of organic matter is positively correlated with the process of hydrocarbon pressurization. On the other hand, the compression coefficient of clay minerals, the formation water content and compacted overpressure have inhibitory effects on hydrocarbon generation and pressurization. The combination of various factors determines the migration and enrichment of crude oil in shale lithology. This study, taking Ordos Basin, one of the most representative basins in China, as a case study, aims to elucidate the mechanisms and parameters involved in the generation and pressurization of hydrocarbons, providing valuable insights for the exploration and development of shale reservoirs in worldwide.

Flexural strength of surrounding columns in URM-Infilled RC frames retrofitted by thick hybrid wall technique

This study investigated the flexural strengthening effect of the Thick Hybrid Wall (THW) technique as a seismic retrofit approach for Unreinforced Masonry Wall (URM)-infilled Reinforced Concrete (RC) frames. THW is a strength–ductility-type seismic retrofit technique, which was developed for pilotis-type RC buildings. In this study, the flexural strength and failure mechanisms of URM-infilled RC frames retrofitted using the THW technique were investigated. Consequently, a comprehensive theoretical model was developed to measure the flexural strength, and a previously proposed equation was modified. Additionally, an equation was developed to determine the minimum additional-wall length, and another equation was developed to determine the demand length of the additional wall to obtain the demand flexural strength. These equations enhance the cost-efficiency and reduce the irregularities risks. The interaction between the URM infill and surrounding RC columns was modeled, and a cyclic loading test was performed under the influence of a constant axial force on the four specimens. The results indicate that THW technique changes the failure mechanism of URM-infilled RC frames from shear to flexure and that the retrofitted URM acts as part of the lateral resisting system owing to the active lateral confinement pressure. The accuracy of the analytical models was confirmed via experimental results, and the developed models facilitate the practical implementation of the THW technique on intended frames.

Artificial Ground Freezing—On the Soil Deformations during Freeze–Thaw Cycles

Artificial ground freezing (AGF) has emerged as a prominent treatment method due to its ability to mechanically strengthen the soil while reducing its permeability. However, its implementation has raised concerns about its impact, particularly with respect to frost heave and subsequent thaw-induced displacements. These soil movements can cause subsidence and pose a significant threat to the integrity of surface structures. Overburden pressure plays a crucial role in AGF and determines the amount of heave generated. This paper presents an analysis of the existing literature about soil freezing and thawing. The aim is to offer an understanding of these processes, specifically with regard to their application in AGF. This paper explains the behavior of soil during freezing, with particular emphasis on the influence of overburden pressure. It also investigates frozen soils’ thawing and freeze–thaw (FT) cycles’ long-term effects on soil properties. AGF offers improved soil strength and reduced water permeability, enhancing construction project stability. However, the interplay between the temperature, soil composition, and initial ground conditions during freezing is complex. This thermo-hydro-chemo-mechanical process strengthens the soil and reduces its permeability, but it can also induce frost heave due to water expansion and ice lens formation. Overburden pressure from the overlying soil limits ice lens growth. FT cycles significantly impact soil properties. In fine-grained soils, FT cycles can lead to over-consolidation, while rapid thawing can generate high pore pressures and compromise stability. Importantly, FT acts as a weathering mechanism, influencing soil properties at both the microscopic and macroscopic scales. These cycles can loosen over-consolidated soil, densify normally consolidated soil, and increase overall hydraulic conductivity due to structural changes. They can also weaken the soil’s structure and deteriorate its mechanical performance.

Effect of Lateral Confining Pressure on Shale’s Mechanical Properties and Its Implications for Fracture Conductivity

The field stress of the shale affects the proppant embedment, fracture conductivity, well production rate, and ultimately the recovery of hydrocarbons from reservoir formations. This paper presents, for the first time, an experimental study investigating the mechanical characteristics of a shale under confining pressures that simulate the in situ stress state in deep reservoirs. Bidirectional but equal confining pressures were applied to the shale sample to replicate its field stress state. Microindentation tests were conducted to assess the alterations of mechanical properties resulting from the application of confining pressures. The results demonstrate a significant increase in Young’s modulus, hardness, and fracture toughness for the samples subjected to confining pressure. Considering the effect of confining pressure, the decrease in proppant embedment is proportional to Young’s modulus of the shale. For larger-sized proppants (e.g., D = 2.50 mm), the influence of confining pressure on fracture conductivity is relatively minor. However, when smaller-sized proppants (e.g., D = 1.00 mm) are used, particularly in scenarios involving shale debris swelling due to prolonged interaction with fracturing fluid, there is a noticeable improvement in fracture conductivity. Importantly, previous computational models have tended to overestimate proppant embedment depth while underestimating fracture conductivity. The findings from this study contribute to advancing the understanding of shale’s mechanical characteristics under in situ reservoir conditions and support the optimization of proppant embedment and fracture conductivity calculation models for the efficient extraction of shale gas.

Research on the bearing creep characteristics and constitutive model of gangue filling body

The creep characteristics and potential deformation patterns of gangue backfill material are crucial in backfill mining operations. This study utilizes crushed gangue from the Gangue Yard in Fuxin City as the research material. An in-house designed, large-scale, triaxial gangue compaction test system was used. Triaxial compaction creep tests were conducted on gangue materials with varying particle size distributions. Analysis was performed based on different particle sizes, stresses, and confinement pressures. The study investigates the creep characteristics of the gangue under different conditions and explores the underlying causes. It reveals the relationship between the creep deformation of gangue materials and the passage of time. Mathematical methods are applied to develop a triaxial compaction creep power law model for gangue backfill materials. Finally, the creep results are fitted using an empirical formula approach.

Method of Average Vertical Earth Pressure for HFCCTs Based on Differential Settlement

AbstractThis paper presents a modified and simplified calculation method, taking into account the differential settlement between the soil columns surrounding the cut-and-cover. High-filled cut-and-cover tunnels (HFCCT) are usually subjected to high earth pressures above the top of the CCT due to an ultra-high backfill. However, the estimation methods for earth pressure above the top of CCT are ambiguous. Through the theoretical analysis of the average vertical earth pressure (AEP) at the top of the CCT, it is found that an additional earth pressure above the top of the overburden pressure is induced, and the magnitude is related to the differential settlement between interior and exterior soil columns. Thus, through a combined theoretical derivation and numerical analysis, a modified formula is proposed. The results show that the vertical earth pressure increment above the top of CCT can be linearly correlated to the differential settlement. In addition, the correlation needs to be calibrated by considering several effects on sites, such as slope angle, groove-width ratios, cross-sectional shape, and the type of backfill. The change in influencing factors has no effect on the function type of the p−δ fitting curve, but it will affect the coefficient k.

Deformation Behaviors of Saturated Clay under Intermittent Cyclic Loading with Cyclic Confining Pressure

Deformation Behaviors of Saturated Clay under Intermittent Cyclic Loading with Cyclic Confining Pressure

MASS-WASTING INDUCED SHIFTS OF THE BASE OF THE GAS HYDRATE STABILITY ZONE: EXAMPLES FROM THE OFFSHORE NIGER DELTA BASIN, NIGERIA

Mass-wasting episodes lead to significant changes in the pressure and temperature regimes within shallow marine sediments and induce variations in the thickness of the gas hydrate stability zone. These variations are marked by vertical migrations of bottom-simulating reflections that typically mark the base of the hydrate zone. Using exploration seismic data from the Offshore Niger Delta, this study presents two examples involving the vertical migration of the base of the gas hydrate stability zones induced by mass-wasting events. The first is related to a slope failure surface along the forelimb of an active thrust-cored anticline with considerable bathymetric relief. Sediment removal has induced both a decrease in overburden pressure and an incursion of cooler temperature flux in strata in the anticline and led to a migration of the base of the gas hydrate stability zone to deeper levels. The second case is related to a recent erosional event that has led to sediment removal along a seafloor channel course. Evidence of ongoing migration of the base of the gas hydrate stability zone to deeper levels is provided by the lateral termination of a BSR along channel wall, its absence beneath the channel bottom and its apparent downward bend close to the channel fringes. Apart from unroofing hydrate systems and releasing free gas into the ocean and possibly the atmosphere, mass-wasting events on the seafloor, represent significant drivers influencing the formation of gas hydrates in shallow subsea sediments and the thickness and depths of the gas hydrate stability zone.

Boundary effect on the soil strength estimation from T-bar penetration tests

The T-bar penetration tests have gained widespread use in assessing the undrained shear strength of marine clays. However, when dealing with model tests or sampled soil with a small diameter of the tube, the reliability of T-bar test results is influenced by both the boundary effect and the soil flow mechanism around the T-bar. In this paper, a comprehensive investigation into the boundary effect on T-bar penetration resistance was conducted by using the large deformation finite element (LDFE) method in conjunction with laboratory tests. The study reveals that the boundary conditions significantly impact the T-bar resistance when the lateral boundary dimension is smaller than 12D. Specifically, the T-bar penetration resistance is underestimated for smooth boundaries and overestimated for rough boundaries. For soils with higher strength, a larger boundary size is required. The bottom boundary also affects the T-bar resistance until the full-flow mechanism is established. However, once the full-flow mechanism is achieved, the boundary effect on T-bar penetration resistance diminishes, even for small lateral boundary sizes (2D). Considering the fact that it is challenging to attain the full-flow mechanism, especially for higher strength soils, a simple algorithm is proposed to estimate soil strength based on a shallow penetration depth (2D). This algorithm is validated through laboratory tests. To address the difficulty in achieving the full-flow mechanism, by applying the overburden pressure during the T-bar test, a novel T-bar test method is suggested. This innovative approach promises to resolve the issue effectively.

Research on dynamic mechanical properties and damage model of ceramic materials under multi‐axial stress

AbstractDue to their exceptional impact resistance, ceramics are extensively used in various fields. However, unavoidable pores, microcracks, and inherent defects can degrade the performance of ceramic materials. A damage model of SiC ceramics under passive confining pressure was constructed based on the Lemaitre strain equivalence principle and the Weibull distribution function. This paper presented a dynamic damage model for SiC ceramics subjected to passive confinement pressure based on the principles of damage mechanics. Additionally, the split Hopkinson pressure bar device was employed to investigate the compressive strength and damage evolution of SiC ceramics at various shock pressures and confinement degrees. The experimental results indicate that constraints can reduce the damage to ceramics. The metal sleeve increased stiffness when compressing the ceramic material, allowing the specimen to convert from brittle–plastic–brittle. When sufficient constraints can be provided, the peak strain decreases gradually with the increase of the impact air pressure. Experimental data showing good agreement with the proposed model validated and analyzed the established model. Thinner boundary constraints cannot maintain the stability of ceramic structures, thicker boundaries do not significantly improve performance, and thicker boundaries can cause more weak areas. This paper provides guidance for the design of encapsulated ceramic composite armor by quantitatively studying the constraint thickness.

Effect of Drying and Wetting Cycles on the Surface Cracking and Hydro-Mechanical Behavior of Expansive Clays

Expansive clays present serious issues in a variety of engineering applications, including roadways, light buildings, and infrastructure, because of their notable volume changes with varying moisture content. Tough weather conditions can lead to drying and shrinking, which alters expansive clays’ hydro-mechanical properties and results in cracking. The hydro-mechanical behavior of Al-Ghatt expansive clay and the impact of wetting and drying cycles on the formation of surface cracks are addressed in this investigation. For four cycles of wetting and drying and three vertical stress levels, i.e., 50 kPa, 100 kPa, and 200 kPa, were investigated. The sizes and patterns of cracks were observed and classified. A simplified classification based on main track and secondary branch tracks is introduced. The vertical strain measure at each cycle, which showed swell and shrinkage, was plotted. The hydromechanical behavior of the clay, which corresponds to three levels of overburden stress as indicated by its swell potential and hydraulic conductivity was observed. It was found that at low overburden stresses of 50 kPa, the shrinkage is high and drops with increasing the number of cycles. Al-Ghatt clay’s tendency to crack is significantly reduced or eliminated by the 200 kPa overburden pressure. The results of this work can be used to calculate the depth of a foundation and the amount of partial soil replacement that is needed.

Аналитическая модель малых колебаний сжимаемой магмы с реологией Максвелла в питающей системе вулкана. Часть 2. Осцилляции вертикальной скорости

The analytical solution for vertical magma movements in a volcanic conduit within the occurrence of low-frequency volcanic seismic events is presented. Magma is described by Maxwell's compressible body model. When the density of the magmatic melt is disturbed, for example, when dense magma enters from deep layers or the melt degasses at a certain depth, density oscillations may occur in the channel as a reaction to this event. For the magma conduit of the simplest cylindrical shape, the magma density and two components of the velocity of movement are subject to oscillations. In this case, the vertical component of the velocity experiences forced oscillations, both under the influence of density oscillations and under the influence of the initiating disturbance. All these oscillations are harmonic damped oscillations, the damping coefficient of which is determined by the relaxation time of the magmatic melt, and the natural frequency depends on the physical characteristics of the magmatic melt and the geometric dimensions of the conduit. Melt density oscillations lead to periodic variations in the lithostatic pressure drop, which in turn causes vertical movements of the melt, the most amplitude along the axis of the magma conduit. The model is used to describe crater surface displacements observed on the surface of the Santiaguito volcano crater.

Confinement-based direct design of square normal and high strength steel tube confined concrete (STCC) short columns

In this paper, a confinement-based direct design model is developed to estimate the axial compression resistance of square steel tube confined concrete (STCC) short columns, which differ from standard concrete-filled steel tube (CFST) columns in load application. While the load in CFST columns is applied to the entire section, it is applied to concrete only in case of STCC columns. Accordingly, STCC columns show superior confinement effect to the concrete core, which will be used directly in the design model. First, the experimental test results of axially-loaded STCC short columns were collected from the literature. The test resistances of the columns were then compared with the predictions obtained by EC4 (2004), American specifications (ANSI/AISC (2010) and ACI 318 R (2014)), AIJ (2001), British standard BS5400 (2005) and CISC (2007), as well as the available design models in the literature. This comparative study showed that all design codes as well as other design models are highly conservative and all do not have the same accuracy over the full range of steel tube slenderness. Then, the resistances of test specimens were used to propose a formula that evaluates the lateral confinement pressure (frp) provided by the steel tube on the concrete core. Finally, the confinement-based direct design model was proposed to estimate the strengths of square STCC short columns. The results of the proposed design model far outperform the available design predictions regardless of the slenderness ratio of the steel tube for all grades of steel and concrete.

Fault Tectonites of the Yenisei Shear Zone (Yenisei Ridge): Evidence and Thermomechanical Numerical Model of Generation of Tectonic Overpressure

Based on the proposed numerical model of the stress-strain state of polymineral rocks, which describes the formation of blastomylonites in the Yenisei Regional Shear Zone (PRSZ) in the Yenisei Ridge, the possibility of local tectonic overpressure exceeding the lithostatic pressure in rocks subjected to shear deformations is shown. For tectonites of the southern (Angara-Kan block) and northern (Isakovka terrane and Garevka complex) segments of the PRSZ, estimates of the maximum overpressure were obtained from 2–3 to 4–5 kbar, which range from 25 to 50% of the lithostatic pressure. It is shown that excess pressures can be preserved in a local volume on a geological time scale sufficient for their fixation in metamorphic minerals. Model values of overlithostatic pressure in garnet-amphibole tectonites and geobarometric estimates of peak values during stress metamorphism allow us to offer new evidence of pressure inhomogeneity in natural mineral associations. Using the results of numerical modeling for the evolution of fault metabasite blastomylonites, it was established that the overpressure at the stage of syn-deformation metamorphism in the shear zone are possible at temperatures up to 600–650°C and not reaching 800°C; the presence of fluid or partial melt prevents the occurrence of overpressure. The amount of excess pressure due to shear stresses depends on the mineral composition and structure of the rock.

Pleistocene to recent evolution of Mocho-Choshuenco volcano during growth and retreat of the Patagonian Ice Sheet

Mocho-Choshuenco volcano (39.9°S, 72.0°W) produced ∼75 explosive eruptions following retreat of the >1.5-km-thick Patagonian Ice Sheet associated with the local Last Glacial Maximum (LGM, from 35 to 18 ka). Here, we extend this record of volcanic evolution to include pre- and syn-LGM lavas that erupted during the Pleistocene. We establish a long-term chronology of magmatic and volcanic evolution and evaluate the relationship between volcanism and loading/unloading of the Patagonian Ice Sheet via twenty-four 40Ar/39Ar and two 3He age determinations integrated with stratigraphy and whole-rock compositions of lava flows and glass compositions of tephra. Our findings reveal that the edifice is much younger than previously thought and preserves 106 km3 of eruptive products, of which 50% were emplaced immediately following the end of the penultimate glaciation and 20% after the end of the LGM. A period of volcanic inactivity between 37 and 26 ka, when glaciers expanded, was followed by the eruption of incompatible element-rich basaltic andesites. Several of these syn-LGM lavas dated between 26 and 16 ka, which crop out at 1500−1700 m above sea level, show ice contact features that are consistent with emplacement against a 1400- to 1600-m-thick Patagonian Ice Sheet. Small volume dacitic eruptions and two explosive rhyolitic eruptions dominate the volcanic output from 18 to 8 ka, when the Patagonian Ice Sheet began to retreat rapidly. We hypothesize that increased lithostatic loading as the Patagonian Ice Sheet grew prohibited dike propagation, thus stalling the ascent of magma, promoting growth of at least three discrete magma reservoirs, and enhancing minor crustal assimilation to generate incompatible element-rich basaltic andesitic to dacitic magmas that erupted between 26 and 17 ka. From an adjacent reservoir, incompatible element-poor dacites erupted from 17 to 12 ka. These lava flows were followed by the caldera-forming eruption at 11.5 ka of 5.3 km3 of rhyolite from a deeper reservoir atop which a silicic melt lens had formed and expanded. Subsequent eruptions of oxidized dacitic magmas from the Choshuenco cone from 11.5 to 8 ka were followed by andesitic to dacitic eruptions at the more southerly Mocho cone, as well as small flank vent eruptions of basaltic andesite at 2.5 and 0.5 ka. This complex history reflects a multi-reservoir plumbing system beneath Mocho-Choshuenco, which is characterized by depths of magma storage, oxidation states, and trace element compositions that vary over short periods of time (<2 k.y.).

Compressive stress-strain model for concrete-filled filament-wound FRP tubes with arbitrary fiber orientation: An analytical approach

An analytical model is proposed to predict the non-linear hoop stress- strain response of multi-laminated fiber reinforced polymer (FRP) tube when subjected to internal pressure. This model incorporates the arbitrary stacking of fiber direction and thickness of individual lamina in FRP tube to effectively calculate confinement pressure exerted by FRP tube on solid concrete columns under uniaxial compression. Next, the model is augmented with Jiang and Teng’s analysis-oriented model to predict the axial behavior of concrete filled FRP tube solid columns with fibers oriented in any arbitrary direction. The predictions by the proposed model are then compared with numerous experimental axial stress-strain/load-strain response of FRP-confined concrete columns collected from the literature. It is found that the present model can closely predicts with the experimental outcomes, outperforming several existing analytical models.

Electrofracturing of Shale at Elevated Pressure

Electrofracturing deeply buried shale formations could be used to increase reservoir permeability and improve reservoir production without requiring large volumes of freshwater. This paper describes a novel experimental system and initial test results to electrofracture shale under high confining pressures. Core-scale laboratory testing was performed on twelve rock samples recovered from a shale gas reservoir. Each sample was subjected to confining pressures of 20.7 MPa (3000 psi) or 58.6 MPa (8000 psi), representative of overburden pressures at depth. Samples were then subjected to application of high voltage until specimen fracture. The experiments produced deformed samples with multiple fracture types, both parallel and oblique to bedding planes. Electrofracturing increased permeabilities by up to nine orders of magnitude for extended time periods. Rock fracture and throughgoing fractures were demonstrated. Computed tomography images revealed the creation of fractures and tube/tunnel flow channels, which resisted closure under hydrostatic pressures up to 58.6 MPa. The breakdown energy and permeability changes in the sample were independent of applied confining pressure. The cumulative energy input required for fracture depended on applied confining pressure and sample length. The energy required to fracture samples up to 9 cm in length is generally more than 0.5 kJ/cm, but no greater than 1 kJ/cm. Our results show that electrofracture of shales under confining pressure is possible and could be a possible water-free mechanism for reservoir stimulation.