Pressure Evolution Research Articles

Temporal evolution of fracture transport properties of fractured shales during long-term stress compaction

Understanding the temporal evolution of fracture transport properties in shales is of increasing importance for the long-term safe operation of many underground engineering projects. Here, a series of long-term (60 days each) water seepage and gas breakthrough experiments utilizing three shale samples, each with a single artificial fracture, was conducted to evaluate the time-dependent evolution of permeability and gas breakthrough pressure (GBP) under constant confining stress. Our results show continuous decreases in permeability and increases in GBP with time, and the rate of change in both is initially rapid but then slows. As the loading time increases, the permeabilities and GBPs become relatively constant. The inferred mechanisms are aperture reductions caused by mechanical creep and clay swelling of fractures. Pretest and posttest scans of fracture surfaces reveal some changes in asperity height, which demonstrates the occurrence of mechanical damage to the fracture during the experiments. Long-term stress compaction causes flow channels to narrow or even partially close over time. The fluid flow in confined fracture is controlled by some narrow apertures in the flow channels, which act as bottleneck points. The apertures at these points decrease to the micro-nano level under stress, significantly reducing fracture transport properties. While the fracture transport properties of fractured shale obviously decrease during long-term stress compaction, residual fracture voids still dominate the fluid flow over a longer period, and are especially prone to gas escape.

Progressive Strain Localization and Fluid Focusing in Mantle Shear Zones during Rifting: Petrostructural Constraints from the Zabargad Peridotites, Red Sea

Abstract This article documents the evolution of pressure and temperature conditions and the successive influence of hydrous melts and aqueous fluids on the operation of extensional shear zones, which exhumed mantle slivers from deep lithospheric or asthenospheric depths, in a rift-to-drift setting. These results are based on a re-analysis of 40 samples from three peridotite massifs of Zabargad island in the northern Red Sea. By integrating high-resolution mapping of the microstructure by electron backscattered diffraction with recent developments in barometry for plagioclase-bearing peridotites and thermodynamic modelling of peridotitic compositions, this study (1) constrains the temporal and spatial evolution of petrological and tectonic processes in the shallow mantle during rifting and (2) documents the presence of melts or aqueous fluids throughout the activity of the shear zones, unravelling substantial feedback between petrological and tectonic processes. Thermobarometry and thermodynamic modelling, constrained by the microstructural observations, document progressive strain localization associated with shearing under decreasing pressure and temperature, from near solidus conditions at >1 GPa (in the north and central peridotite massifs) or ~ 0.7 GPa (in the southern massif) to <600°C and < 0.3 GPa in all three massifs. The data substantiate local aqueous fluid saturation in the shear zones. This together with higher contents of hydrous minerals in ultramylonites indicate fluid focusing in the shear zones, with seawater ingress extending to >10 km depth. The presence of melts or fluids enabled concurrent dislocation and dissolution–precipitation creep, resulting in weakening of the shear zones. However, fluid supply was spatially heterogeneous and likely intermittent, with equilibrium achieved only locally in the ultramylonites. The present study documents therefore how the feedback between progressive strain localization and fluid focusing in extensional shear zones contributes to thinning and exhumation of the mantle during continental rifting and the rift-to-drift transition.

Flameless venting characteristics and design model of micro-nano PMMA dust explosion

The effects of Fe–Ni foam thickness and dust size on flame propagation, reduced overpressure, and venting efficiency in 30 μm and 150 nm polymethyl methacrylate (PMMA) dust explosions were investigated. The flame quenching mechanism was revealed by coupling the heat transfer and flow of the dust flame within the Fe–Ni foam. It is found that micron dust is more prone to quenching than nano dust, and the differences in the quenching process of micro-nano dust are explained by combining the dust combustion kinetics and the theory of inter-particle heat transfer. The pressure venting mechanism of micro-nano dust was analysed under different thicknesses of Fe–Ni foam, and the thermal expansion effect of the flame passing through the Fe–Ni foam and its flow resistance significantly increased the reduced explosion overpressure. The flow continuity of the micro-nano dust was classified by means of the Knudsen number (Kn), which elucidates the effect of dust size differences on the pressure evolution. A prediction model for the maximum reduced explosion overpressure is proposed based on the explosion pressure venting of micro-nano dust. Changes in vented pressure have a direct impact on the efficiency of flameless venting. Nano-dust has an efficiency of more than 20 % lower than that of micron dust.

Differential evolution of pore fluid pressure in the Sinian carbonate reservoirs of the central and eastern Sichuan Basin, China: Implication for gas preservation and destruction

Trillions of cubic meters of gas reserve have been found in the Sinian Dengying carbonate reservoirs with normal pressure in the central Sichuan Basin, while no industrial gas reservoir have been detected in the Sinian Dengying reservoir with normal pressure in the eastern Sichuan Basin. The pore fluid pressure of gas reservoir is usually closely related to total gas content. To investigate the pore fluid pressure evolution and its implication for gas reserve preservation in the Sinian Dengying reservoir of the central and eastern Sichuan Basin, we conducted a comprehensive analysis including fluid inclusion petrography, microthermometry and Raman spectroscopy. The timings of gas inclusions captured in the central and eastern Sichuan Basin occurred from 175 to 92 Ma and 191 to 183 Ma, respectively. The presence of two‐phase vapour‐solid bitumen inclusions with similar phase proportions in a single fluid inclusion assemblage of fluorite provides direct evidence of in situ oil cracking to gas. The widespread solid bitumen from the Sinian Dengying reservoir in the central Sichuan Basin indicates the existence of massive oil cracking, which results in the formation of overpressure in the reservoir. Pore fluid pressure evolution of the Sinian Dengying reservoir of the central Sichuan Basin experiences normal pressure stage (200–155 Ma), overpressure development stage (155–90 Ma) and overpressure release stage (90–0 Ma). The maximum pore fluid pressure and its corresponding pressure coefficient of the Sinian Dengying reservoir of the central Sichuan Basin are approximately 141.4 MPa and 1.95, respectively. The overpressure development stage reflects the processes of oil cracking and gas accumulation, and the overpressure release stage reflects the dissipation of some natural gas in the Sinian Dengying reservoir of the central Sichuan Basin. The pore fluid pressure of the Sinian Dengying reservoir in the eastern Sichuan Basin has maintained at normal pressure since 200 Ma, indicating that the gas reservoir was small during the oil cracking stage and natural gas completely leaked due to tectonic uplift.

Coupled modeling and simulation of tank self-pressurization and thermal stratification

Numerical analysis of thermo-fluid dynamics for cryogenic propellant storage primarily consists of nodal and computational fluid dynamics (CFD) modeling approaches. While nodal approaches prioritize faster computation over fidelity, CFD approaches promise accuracy and fidelity at the expense of significant computational resources. This paper presents an efficient coupling methodology developed to facilitate the simulation of a long-term self-pressurization process of a cryogenic propellant tank as well as associated thermal stratification phenomenon under both normal and reduced gravity conditions. Key highlight of the methodology is the development of a coupling scheme based on a domain decomposition approach that separates the tank into two computational regions at the liquid-vapor interface. SINDA/FLUINT, the nodal code, is utilized to simulate the liquid region, while ANSYS Fluent, the CFD code, handles the vapor region. A data exchange algorithm was developed to compute required boundary conditions for each region using the local thermodynamic properties of assumed infinitely thin interface. The coupling between the nodal and CFD codes was demonstrated by simulating a self-pressurization process in a small size tank using hydrogen as the working fluid. A sensitivity study on the grid sizing and coupling time step was conducted to determine appropriate spatial and ensure a divergent-free explicit data exchange time step size. Using the coupling approach, two numerical case studies were performed to study tank self-pressurization by considering two initial hydrogen fill levels. The effectiveness and efficiency of the coupling methodology was assessed by comparing the temperature and pressure evolution results of the coupled simulation with those obtained solely from the CFD simulation. Results showed that the coupling scheme and data exchange algorithm were successfully implemented, and the coupled simulation agreed well with the CFD simulations. In addition, a stratification number was used to characterize the transient dynamic development of the thermal stratification. Lastly, the computational costs associated with both approaches were compared. Significant reductions in simulation time were achieved for both cases.

Pressure-Induced Exciton Formation and Superconductivity in Platinum-Based Mineral Sperrylite.

We report a comprehensive study of Sperrylite (PtAs2), the main platinum source in natural minerals, as a function of applied pressures up to 150 GPa. While no structural phase transition is detected from pressure-dependent X-ray measurements, the unit cell volume shrinks monotonically with pressure following the third-order Birch-Murnaghan equation of state. The mildly semiconducting behavior found in pure synthesized crystals at ambient pressures becomes more insulating upon increasing the applied pressure before metalizing at higher pressures, giving way to the appearance of an abrupt decrease in resistance near 3 K at pressures above 92 GPa consistent with the onset of a superconducing phase. The pressure evolution of the calculated electronic band structure reveals the same physical trend as our transport measurements, with a non-monotonic evolution explained by a hole band that is pushed below the Fermi energy and an electron band that approaches it as a function of pressure, both reaching a touching point suggestive of an excitonic state. A Lifshitz transition of the electronic structure and an increase in the density of states may naturally explain the onset of superconductivity in this material.

Experimental study on the influence of roadway shape on the evolution of outburst fluid static pressure

To explore the static pressure dynamic disaster mechanism of coal-and-gas outburst (CGO) fluid, the self-developed multi-field coupling large-scale physical simulation test system of coal mine dynamic disaster was used to carry out gas outburst and CGO physical simulation tests in straight, L-shaped and T-shaped roadways. The influence of roadway shape on the evolution of static pressure was explored, and the role of pulverized coal in the process of static pressure dynamic disaster was clarified. The results indicated that the static pressure showed a fluctuating downward trend during the outburst process. When gas outburst, the middle and front parts of the roadway in the straight section roadway were the most serious areas of static pressure disasters in the three shapes of roadways. The duration and range of high static pressure disaster in L-shaped roadway were larger than those in T-shaped and straight roadways in turn. When CGO, the most serious area of static pressure disaster in L-shaped and T-shaped roadways moved backward to the middle of the straight section roadway, and there was a rebound phenomenon in the process of static pressure fluctuation decline, which showed the pulse characteristics of CGO. During the outburst, the static pressure dynamic disaster hazard of L-shaped roadway was higher than that of T-shaped roadway, and the static pressure at the bifurcation structure decayed faster than that at the turning structure, which indicated that T-shaped roadway was more conducive to the release of static pressure in roadway, thus reduced the risk of static pressure disaster. When gas outburst, the static pressure attenuation of the fluid in the roadway before and after the turning and bifurcation structure was greater than that of CGO. The peak static pressure and impulse of the fluid during gas outburst were 2 times and 4–5 times that of CGO respectively. The presence of pulverized coal reduced the attenuation of static pressure and the hazard of dynamic disaster, prolonged the release time of energy, and led to the change of the maximum static pressure disaster area.

Assessing the Swallowing Function in Children with Spinal Muscular Atrophy: An Easily Accessible and Objective Multidimensional Approach.

Spinal muscular atrophy (SMA), a genetic neuromuscular disease caused by lack of survival of motor neuron (SMN) protein, is characterized by muscular atrophy and respiratory and bulbar dysfunction. While swallowing disorders are common, they remain poorly studied. Our study aimed to explore 1) intraoral pressure measurements with the Iowa Oral Performance Instrument system and the reliability of a Swallowing Function Assessment Questionnaire (SFAQ) in healthy controls, and 2) evaluate their use as swallowing function biomarkers and the evolution of swallowing function over time in children with SMA. We recruited 53 healthy children and 27 SMA patients all treated with SMN gene modulator therapy. Participants completed the SFAQ and underwent at least one measurement of maximal oral pressures (lingual, labial, and masseter). Mean oral normalized pressure index were lower (all sites p < 0.001) and mean SFAQ scores were higher (p < 0.001) in patients compared with healthy controls. Pressure evolution over 1 year in SMA patients for all three oral sites did not show significant differences. SFAQ scores correlated negatively with oral pressures at all three sites in patients. Both tools provided new insights on the oral and pharyngeal phase of swallowing in SMA patients. In SMA patients, muscle strength in certain crucial anatomical regions during swallowing is weaker than in healthy children.

Fast shot speed induced microstructure and mechanical property evolution of high pressure die casting Mg-Al-Zn-RE alloys

In this study, the effects of fast shot speeds during high pressure die casting on the microstructure and mechanical properties of Mg-Al-Zn-RE (RE: rare earth) alloys were systematically investigated. The optimum mechanical performance was achieved at a fast shot speed of 6 m/s, and the ultimate tensile strength, yield strength, and elongation of the castings reached 290 MPa, 190 MPa, and 10.5 %, respectively. With an increase in fast shot speed, the yield strength, ultimate tensile strength, and elongation of the Mg-Al-Zn-RE alloy increased by 17 MPa, 82 MPa, and 8.2 %, respectively. These improvements are primarily attributed to the decreased area fraction of externally solidified crystals (ESCs) and the reduced volume fraction of pores. Furthermore, the enhancement in yield strength is due to grain boundary strengthening, solid-solution strengthening, and second-phase strengthening. The reduction in the area fraction of ESCs and porosity are the main contributors to the improvement in plasticity. The findings of this study provide valuable guidance for the intelligent design of novel high pressure die casting Mg alloys.

Experimental Study of the Earth Pressure Evolution on a Model Wall Rotating about Its Base

Experimental Study of the Earth Pressure Evolution on a Model Wall Rotating about Its Base

Thermal evolution differences of reservoir bitumen and their implications: A case study of the Moxi area in the central Sichuan basin

Temperature and time were generally considered as the two key influences on the thermal evolution of both source organic matters and secondary hydrocarbon products (i.e., oil, gas, bitumen and solid bitumen). And for the hydrocarbons, other factors such as the types of source organic matters, the alteration reactions and fluid pressure evolution can also influence their degree of thermal maturation. As a consolidated product of bitumen, the traditional view is that the solid bitumen originated from the same source would exhibit similar maturity after experiencing identical paleo-temperature. However, things need to be more thoughts, such as the impact of system open or not on the solid bitumen thermal evolution and maturation degree. In this regard, we compared the solid bitumens within both reservoir pores and inclusions in deep carbonate reservoirs of lower Cambrian Longwangmiao Formation (Є1l) and the fourth member of the Sinian Dengying Formation (Z2dn4) in the Moxi area in the central Sichuan Basin. And by analyses of the Raman spectroscopy and bitumen reflectance, our results show a significant difference of maturities for these homologous solid bitumens after experienced the same highest geological temperature. Specifically, based on petrological observations, three types of solid bitumen occurrences (Bit. A, Bit. B, and Bit. C) were identified. Bit. A fills the early fine-grained dolomite dissolution pores with small and dispersed morphology, which eRo-Raman (equivalent vitrinite reflectance obtained by Raman) values show a narrow range from 2.60% to 2.80%. Bit. B with larger, blocky morphology, distributes within pores between the early recrystallized dolomites or the subsequent euhedral dolomites, including the bitumen filling in the fracture as stylolite. Their eRo-Raman values mainly concentrate in the range of 1.80%–1.90%. Bit. C refers to the bitumen inclusions hosted in various diagenetic minerals, with eRo-Raman values range from 2.70% to 2.87%. Since these solid bitumens originated from the same source rocks and have experienced the same highest geological temperature, their heterogeneous eRo-Raman values, therefore, suggest that whether the system open or not matters the thermal evolution of solid bitumen. Our results suggest that caution should be applied when using maturity to study the thermal evolution history in an open system, and hydrocarbons trapped in a closed system (e.g., fluid inclusion) can serve as a more credible recorder of thermal evolution.

Framework for Designing of Wireless Sensor Network Using OPNET and Effect of Transport Protocols on Simulation

A Wireless sensor network can be defined as a network of devices that can communicate the information gathered from a monitored field through wireless links. The data is forwarded through multiple nodes, and with a gateway, the data is connected to other networks like wireless Ethernet. It is intended for a general application and should be able to collect data from many nodes, every node connected to several sensors. One possible application for such a network is in the medical area. At first the network will be used to display the evolution of blood pressure; the body temperature, the ambient temperature and pressure and the level of the transfusion liquid can be collected as well. The network coordinator will transmit the data to a local server for further processing. The simulation will be used to evaluate the general parameters of the wireless network and to optimize it. In this paper, we aim to evaluate the performance of a ZigBee wireless sensor network using OPNET and also study the effects of TCP and UDP on the performance of the application based on OPNET simulation software. Keywords-Sensor, wireless sensor network, ZigBee, OPNET, TCP, UDP.

Robustness of the pyrochlore structure in rare-earth A2Ir2O7 iridates and pressure-induced structural transformation in IrO2

A comprehensive study of the structural properties of the heavily investigated rare-earth A2Ir2O7 iridate series under extreme conditions is presented. From Pr2Ir2O7 to Lu2Ir2O7, the series is sufficiently covered by iridates with A = Pr, Sm, Dy, Ho, Er, Tm, Yb, and Lu; general trends and systematics within the series, including the understudied heavy-rare-earth members, are dependably followed. Temperature- and pressure-dependent synchrotron X-ray powder diffraction experiments reveal robustness of the pyrochlore structure throughout the series, down to 4 K and up to 20 GPa. The thermal expansivity of the pyrochlore lattice is determined, all falling in the Debye temperature range of θD = 360–420 K. The pressure compressibility shows a systematic increase of the bulk modulus with the rare-earth atomic number from K = 180–210 GPa. Combining the results of thermal measurements (Debye temperature) and pressure measurements (bulk modulus) enables us to determine the Grüneisen parameter of selected members and compare it to previous studies. Temperature and pressure evolution of the fractional coordinate of oxygen at 48f Wyckoff position, the sole free fractional coordinate in the crystal structure, is investigated and discussed regarding the antiferromagnetic ordering of the Ir magnetic moments. In addition to results on A2Ir2O7 iridates, the temperature and pressure evolution of the crystal structure of an IrO2 minority phase is followed. The tetragonal rutile-type structure is stable down to the lowest temperature. However, an application of pressure of approximately 15 GPa induces a structural transition: The tetragonal structure is orthorhombically distorted. The orthorhombic structure is still not fully stabilised at 20 GPa, and further distortion of the lattice (or subsequent structural transformations) is expected with increasing external pressure.

High pressure phase transition and its influence on structural, mechanical properties and elastic anisotropy of [formula omitted]: An ab-initio study

Lithium carbide (Li2C2), a promising tritium breeding material with potential applications in magnetic confinement-based fusion reactor blankets, has drawn significant attention due to its recent utilization in lithium-ion batteries. In the current study, we employed first-principles calculations with van der Waals (vdW) force correction to explore the structural and mechanical properties of Immm and Pnma phases of Li2C2 subjected to external hydrostatic pressure. It is demonstrated that inclusion of vdW effects accurately predicts Immm→Pnma phase transition at 16 GPa, aligning closely with experimental transition pressure. In contrast, PBE-GGA calculations underestimate the same by about 21%. Current paper is the first comprehensive study of pressure evolution of mechanical properties and strength determining parameters of Li2C2. Interestingly, this inherently brittle material exhibits ductile characteristics beyond 7.5 GPa. The paper also offers a quantitative comparison of its strength parameters with other prominent tritium breeding materials. Finally, the strong directional dependence due to the presence of C2 dimer is investigated by analyzing the pressure variation of elastic anisotropy. The study has its relevance in assessing structural integrity of Li2C2 during inadvertent buildup of tritium and helium that would generate stress in the solid breeder.

Large-Scale Experimental Investigation of Hydrate-Based Carbon Dioxide Sequestration

Hydrate-based CO2 sequestration is a novel approach that can not only realize permanent CO2 sequestration but can also form an artificial cap to prevent its upward migration. In this work, a self-developed large-scale 3D apparatus was employed to investigate hydrate formation characteristics in hydrate-based CO2 sequestration at a constant liquid CO2 injection rate through a vertical well for the first time. Temperature and pressure evolutions in the sediment were analyzed in detail. Key indicators, including cumulative sequestered CO2, CO2 in hydrate and liquid phases, the instantaneous hydrate conversion, and liquid CO2 retention rates, were calculated. The results show that hydrate continuously forms with increased CO2 injection and exhibits strong heterogeneity due to the variation in hydrate formation rate and quantity. Severe liquid CO2 heterogeneous figuring phenomena occur since hydrate deteriorates the effective pore structure and topology, resulting in relatively small cumulative sequestered CO2 when a large amount of CO2 is released from the outlet. Meanwhile, the instantaneous hydrate conversion and liquid CO2 retention rates have large fluctuations owing to water consumption and variation in the effective contact area between liquid CO2 and water. However, hydrate formation does not cause blockage of wellbore and formation nearby under given experimental conditions, which is beneficial for hydrate formation in deeper sediment. This study provides insights into hydrate formation and liquid CO2 immigration regularity during hydrate-based CO2 sequestration and demonstrates its feasibility at a field scale.

The effect of pressure evolution on flame propagation dynamics of H2/CH4 mixtures explosion in a horizontal closed duct

To investigate the effect of explosion pressure on flame propagation of H2/CH4 mixtures, the pressure dynamics of H2/CH4 mixtures explosion with different volume fractions of hydrogen (0, 0.2, 0.4, 0.6, 0.8, 1 (×100/%)) and equivalence ratios (0.8, 1, 1.2, 1.4) is measured using 2 pressure sensors in a horizontal duct with ignition electrode position not at the end. The flame propagation characteristic is studied using images recorded by a high-speed camera. Through the analysis and discussion of the experimental results, the interaction among explosion pressure, flame front, and flow field are discussed. The results show that when the volume fraction of hydrogen is greater than 0.6, the rate of explosion pressure rises, the flame front position, and the flame front speed are greatly improved. At higher and lower equivalence ratios, it is easier to form distorted “tulip” flames. As the volume fraction of hydrogen increases, the inclination angle of the flame front decreases, and becomes a typical “tulip” flame gradually. The convection of the flow field is an important cause of pressure oscillation, which makes the pressure distribution uneven, and its influence on Pmax, (dP/dt)max, and tc is weak. As the volume fraction of hydrogen increases, the duration of pressure oscillation decreases, and the intensity of pressure oscillation increases. The pressure wave has a substantial impact on the flame front propagation of distorted “tulip” flames and the pressure history of typical “tulip” flames.

Numerical modelling of pore water pressure response beneath a raft foundation during real river floods

Tall buildings with basement levels are increasingly being built due to need for space in large cities. Frequently, such structures are built involving a raft foundation and diaphragm walls below the water table. In addition, sometimes such buildings are located on floodplains. Therefore, if a river flood event occurs, the building can be exposed to pore water pressure (due to the fluctuation of water table) acting beneath its raft foundation. The generated subpressures will depend on the water table changes with time, and on the way such pressures are transmitted through the ground. Previous works have studied this behavior through laboratory and small-scale tests or numerically; however, many of them have used a constant hydraulic gradient and the water table fluctuations with time have been ignored. In this work, the evolution of pore water pressures with time mobilized beneath a raft foundation of a building built in a floodplain is studied. To do that, full-scale numerical models capable of simulate a river flooding and its corresponding overflow are developed. Such models incorporate data from water table change–time curves recorded during real river floods associated with a set of river regimes. Additionally, the effect of factors such as the soil permeability, the diaphragm wall length, and the soil thicknesses on water pore pressures beneath a raft foundation are also analyzed. Results suggest numerical models developed herein are capable of reproducing pore pressures induced beneath a raft foundation during river flooding. Furthermore, it was found that the above-mentioned factors could impact the percentage of pore water pressure mobilized beneath the raft foundation with respect to the maximum pore water pressure that could be induced during river flooding, and that the principal risk arises in buildings near large catchments where the flow increases over an extended period. Finally, practical implications and recommendations to practitioners are provided.

Anthropogenic pressure in Czech protected areas over the last 60 years: A concerning increase

This article focuses on the evolution of anthropogenic pressure across Czech large-scale protected areas (protected landscape areas and national parks, n = 30) over the last 60 years. In four periods (1960s; 1990; 2004; between 2016 and 2020) we analysed the development of artificial structures (built-up areas, recreational areas, roads, dirt roads, and streets) and their impact on landscape fragmentation. These spatial data were derived from topographic maps and aerial imageries and then statistically compared. Principally, built-up and recreational areas have increased; however, intensity varied across protected areas (PAs). Built-up areas have grown more in PAs close to large towns, especially after 1990 as protection did not prevent suburbanization in the PAs. Furthermore, PAs with more built-up areas also have more buildable areas; therefore, further ongoing development is expected. Recreational areas are present the most in some mountainous areas, such as ski resorts, and near large towns and spa towns (e.g. golf courses). The density of roads was more or less stable during the study period. Dirt road density differed within PAs according to the prevalent type of landscape: growth or stagnation in forested areas due to recreation and logging purposes and a decline in agricultural land, mainly as a consequence of collectivization in 1950 s followed by landscape unification and the creation of large patches of agricultural land. To sum up, anthropogenic pressure increased with landscape fragmentation, but these impacts are different across Czechia; in peripheral, attractive or peri-urban areas, which is important from landscape management point of view.

Aquathermal effect of anomalous pressure generation in consolidating minefill

Recycling cement-amended tailings into subsurface cavities has delivered competitive socioeconomic revenue for underground mining. However, recent instances of anomalous thermal pressure in consolidating backfill have raised growing concerns over the current design philosophy. This study demonstrates that the excellent hydraulic sealing and considerable chemical energy inherent in cemented backfill can spontaneously generate substantial thermal pressurisation through constrained pore fluid expansion. An analytical solution is hence developed for characterising the non-isothermal behaviour of hydrating backfill based on classical thermo-poroelasticity. The influence of the preparation condition and mix design on the pressure evolution in the time domain and during spontaneous heat generation is then thoroughly examined, successfully pinpointing the causal mechanism responsible for typical thermal pressure anomalies. It is demonstrated that the anomalous pressure is attributable to both the conservative use of binder, which increases the intrinsic heat load, and the elevated initial temperature, which promotes water volume expansion. The fundamental influence of temperature-sensitive water expansivity on the path dependence of thermal pressurisation is also elucidated. This study thus contributes to a comprehensive understanding of the thermally correlated pressure anomalies that frequently occur in field operations. These critical findings would also hold practical implications for designing successful backfill solutions in challenging mine environments.

Undrained behavior of marine clay under one-way cyclic loading with variable confining pressure

Settlement of roads or railway caused by traffic loading has a serious effect on the safety and service performance of transport infrastructures constructed on soft marine clay. While simple cyclic triaxial test with constant confining pressure (CCP) were used in most of the previous studies, a series of cyclic triaxial tests with variable confining pressure (VCP) were carried out on normally consolidated (NC) and overconsolidated (OC) reconstituted Wenzhou soft clay in this paper to study the undrained behavior of soft marine clay due to surcharge preloading as well as cyclic traffic loading. VCP test is able to approximate the complicated stress path than CCP test caused by traffic loading. The test results indicate that NC specimens show significantly different pore water pressure (u) evolution compared with OC specimens. However, a change in the overconsolidation ratio (OCR) of OC specimens does not have a significant influence on variation of u with identical cyclic stress ratio (CSR) and total stress path (η). The slope of the effective stress path is dependent on the total stress path under which the specimen was loaded cyclically, regardless of the OCR and whether variable confining pressure was applied. The slope of the effective stress path is broadly in line with the slope of corresponding total stress path. In addition, the development of permanent axial strain (εpa) due to one-way cyclic loading was shown to depend significantly on the values of η and OCR. Both the variable confining pressure and OCR limited the strain accumulation of saturated marine clay under undrained one-way cyclic loading. Finally, the effects of η and OCR on the magnitude of εpa after 1000 loading cycles are quantified and incorporated in a power law function for the permanent deformation prediction of soft marine clay due to traffic loading.