Macroscopic Physical Properties Research Articles

The influence of pore throat heterogeneity and fractal characteristics on reservoir quality: A case study of chang 8 member tight sandstones, Ordos Basin

The Chang 8 member of the Yanchang Formation in the Ordos Basin exhibits extensive development of tight sandstone reservoirs. In comparison to conventional reservoirs, these tight sandstone reservoirs demonstrate smaller pore-throat systems and stronger heterogeneity due to interactions between inherent sedimentary components and various diagenetic processes. To further investigate the influence of microscopic pore throat structure on macroscopic physical properties and oil content within the reservoir, a comprehensive study was conducted utilizing high pressure mercury injection, nuclear magnetic resonance, X-CT scanning, and other pore throat testing methods. This study was complemented by observation techniques such as polarizing microscope, scanning electron microscopy, and laser confocal imaging, to study the pore throat system of reservoirs under the influence of different sedimentary components and diagenesis. By comparison, it is observed that the radius of the primary pore throat system in the tight sandstone reservoir ranges from 0.01 to 1 μm. The structural characteristics of the pore throat system significantly impact the macroscopic physical properties of the reservoir. Due to variations in testing methods, high pressure mercury injection, nuclear magnetic resonance (NMR), and X-ray computed tomography (X-CT) reveal different fractal dimensions of the reservoir's pore throat system. Therefore, it is better to respectively utilize fractal dimension Df2, Df2-NMR, Df2-CT, and pore throat parameters to characterize the microscopic pore throat system with a radius ranging from 0.01 to 1 μm. The decrease in the average pore throat radius and the increased irregularity of pore shape contribute to heightened heterogeneity in the micro-pore throat structure within the reservoir. This negatively impacts its physical properties and oil content. Furthermore, it is important to note that the minimum threshold of pore throat radius plays a crucial role as a primary factor determining the fluid seepage capacity within this reservoir. Moreover, when isolated pores exist, reduced fluid mobility ensues, which further worsens the seepage conditions of the reservoir. The chlorite rims development reservoir shows a low fractal dimension in its micro-pore throats, contributing to superior macroscopic petrophysical properties and oil content. However, compression, siliceous cementation, and calcite cementation negatively impact the average pore throat radius by increasing micropores, inaccessible pores, and narrow throat content. This results in a stronger heterogeneity of the pore throat structure, leading to poor seepage conditions and lower oil content.

Prediction of crude oil physical properties based on molecular compositional modeling approach

AbstractIn this study, the Structural Units‐Bonding Matrix will be introduced into the crude oil characteristics analysis, specifically engineered to depict the molecular intricacies of petroleum substances. This methodology synergizes the bonding matrix with structural units, assigning the bonding matrix to the foundational layer, while the structural units adorn the surface layer. Through meticulous analysis of crude oil data, this study identified the core and branched molecular constituents of crude oil, facilitating the digital articulation of these molecules. Leveraging this foundational work, this study developed composition models for five quintessential types of crude oil, enabling the precise prognostication of their macroscopic physical properties. Further, by evaluating the viscosity‐temperature characteristics of these selected crude oils, this study established a predictive model for the viscosity–temperature relationship of crude oils, grounded in the quantitative structure–property relationship method. This approach not only augments this study understanding of crude oil molecular composition but also enhances the predictive accuracy of their physical properties, heralding a significant advancement in the field of petroleum molecular science.

Influence of Nano-Silicon Dioxide in the Enhancement of Surface Structure of Public Filler and Properties of Recycled Mortar

This paper proposes a method of enhancing public filler (PF) with nano-SiO2 (NS) to prepare modified recycled aggregate mortar (RAM). The improvement effect of NS solution at different concentrations and immersion times on the macroscopic physical properties of recycled public fine aggregates (PFA) was investigated. Moreover, the effect of NS on the basic physical properties and durability of recycled mortar (RM) and the reinforcement mechanism of NS on recycled mortar was analyzed through various techniques. Results indicated that the modification effect of NS could remove loose cement mortar from the surface of PFA. It reacted with calcium hydroxide and calcite to generate nano-particles that could fill pores in PFA. The water absorption rate of PFA decreased to 9.3% when immersed in 2% NS solution for 72 h. There was no significant improvement in the mechanical properties of RM when the solution concentration and immersion time were increased. However, the compressive strength of RM prepared by modifying PFA with 2% NS was increased by about 21.9%, and the capillary water absorption and electric flux were reduced by 56.3% and 15.1%, respectively. Micro-analysis results showed that the volcanic ash effect of NS enabled it to react with Ca(OH)2 adhered to the surface of PFA, generating C-S-H and improving the interfacial bonding of PFA. Moreover, NS adsorbed on the surface of PFA dispersed into the freshly mixed cement slurry, which further enhanced the internal structure of PFA.

Semi-Solid Forging Process of Aluminum Alloy Connecting Rods for the Hydrogen Internal Combustion Engine

As an important piece of equipment for hydrogen energy application, the hydrogen internal combustion engine is helpful for the realization of zero carbon emissions, where the aluminum connecting rod is one of the key core components. A semi-solid forging forming process for the 7075 aluminum alloy connecting rod is proposed in this work. The influence of process parameters, such as the forging ratio, sustaining temperature, and duration time, on the microstructures of the semi-solid blank is experimentally investigated. The macroscopic morphology, metallographic structure, and physical properties of the connecting-rod parts are analyzed. Reasonable process parameters for preparing the semi-solid blank are obtained from the experimental results. Under the reasonable parameters, the average grain size is 41.48~42.57 μm, and the average shape factor is 0.80~0.81. The yield strength and tensile strength improvement ratio of the connecting rod produced by the proposed process are 47.07% and 20.89%, respectively.

Microscopic Characterization and Fractal Analysis of Pore Systems for Unconventional Reservoirs

The complex pore structure of unconventional oil and gas reservoirs is one of the reasons for the difficulties in resource evaluation and development. Therefore, it is crucial to comprehensively characterize the pore structure, understand reservoir heterogeneity from multiple perspectives, and gain an in-depth understanding of fluid migration and accumulation mechanisms. This review outlines the methods and basic principles for characterizing microporous systems in unconventional reservoirs, summarizes the fractal analysis corresponding to the different methods, sorts out the relationship between the fractals and reservoir macroscopic physical properties (porosity, permeability, etc.) with the reservoir microscopic pore structures (pore structure parameters, pore connectivity, etc.). The research focuses on cutting-edge applications of characterization techniques, such as improved characterization accuracy, calibration of PSD ranges, and identification of different hydrogen compositions in pore systems for dynamic assessment of unconventional reservoirs. Fractal dimension analysis can effectively identify the quality level of the reservoir; complex pore-throat structures reduce permeability and destroy free fluid storage space, and the saturation of removable fluids is negatively correlated with Df. As for the mineral composition, the fractal dimension is positively correlated with quartz, negatively correlated with feldspar, and weakly correlated with clay mineral content. In future qualitative characterization studies, the application and combination of contrast agents, molecular dynamics simulations, artificial intelligence techniques, and 4D imaging techniques can effectively improve the spatial resolution of the images and explore the adsorption/desorption of gases within the pores, and also help to reduce the computational cost of these processes; these could also attempt to link reservoir characterization to research on supercritical carbon dioxide-enhanced integrated shale gas recovery, carbon geological sequestration, and advanced underground hydrogen storage.

Quantitative characterization of microstructure and research on spatial variation characteristics of loess of different strata in Luochuan, Shaanxi, China.

The complete sequence of loess strata in Luochuan has become a typical section in loess strata, and is the main focus of research for many scholars studying loess. We were based on the theory of aeolian loess and established a set of quantitative index parameters for loess microstructure through our previous research, such as equivalent diameter, sphericity, morphology ratio, orientation angle Phi, orientation angle Theta, pore Eq-Radius, throat Eq-Radius and throat channelLength. Through the quantitative characterization of various index parameters of the Luochuan loess, we found that the probability density of each index parameter meets a specific distribution well, and in terms of spatial dimension, it shows that as the depth of the strata increases, the average particle size and the mode of pore Eq-Radius, throat Eq-Radius and throat channelLength generally increase, while the mode of particle morphology ratio generally decreases. In addition, loess particles in deeper strata are less prone to vertical sedimentation and tend to deposit gently or horizontally. Most particles in different strata are distributed in a northwest or southwest direction. During the formation period of strata, the main cause for spatial differences is the material carrying force. We conducted a statistical analysis on the correlation between the macroscopic physical properties of loess and its microstructure index parameters. Specifically, we found a positive correlation between loess density and the average particle size and the mode of particle equivalent diameter, Additionally, we found a negative correlation between loess liquid limit and plastic limit, and the mode of particle morphology ratio. Furthermore, there was a negative correlation between permeability coefficient and the mode of pore Eq-Radius, throat Eq-Radius, and throat channelLength.

Preparation method and applicability evaluation of 3D printing alumina ceramic artificial coarse aggregate

Abstract The particle size and morphology of crushed stones impact their macroscopic mechanical and physical properties, which has become a hot topic in the study of road and geotechnical engineering. However, some reported studies fail to control the particle morphology as the only independent variable. This paper presented a new method to print artificial aggregates based on 3D printing technology of particles. The applicability of the new method was verified with uniaxial compression and dynamic modulus tests of asphalt mixtures formed by the printing aggregates. Results showed that the printing aggregates earned similar physical properties to real coarse when sintered at 1400℃ with alumina ceramic powder and CuO: TiO2 a 1:2 additive in mass. Besides, the gross volume density, compressive strength, and shrinkage of the printing aggregates show a similar trend of increasing and then decreasing with the increase of additives. The optimal mass percentage of additives was obtained to be 5%. Mechanical tests indicated that the mechanical indexes of the asphalt mixtures formed with the two types of coarse aggregates were similar, while the results of the specimens formed with artificial coarse aggregates showed less dispersion. The stability of test results was significantly improved for different asphalt mixture specimens prepared with 3D printed coarse aggregate. This provides a basic method for further research on the multi-scale properties of particle material.

Preliminary study on the mechanical behavior of clay in one-dimensional compression with DEM simulations

The mechanical behavior and physical properties of clay are closely associated with its microstructure. Current research on the macroscopic mechanics and physical properties of clay is comprehensive and systematic. However, the microstructural variations underlying these characteristics have been predominantly examined under mercury intrusion porosimetry and scanning electron microscopy, while quantitative and systematic studies are notably limited. This research employs the discrete element method (DEM) simulation to investigate the microscopic responses of clay, simulating one-dimensional compression tests on two clay types: card-house and book-house structures. The analysis of pore size and morphology was conducted using virtual mercury intrusion porosimetry and the pore segmentation method. The clay microstructure was quantitatively characterized by parameters such as pore aspect ratio, orientation distribution, and cumulative pore volume curve. The findings demonstrate that DEM effectively replicates the fundamental mechanical behavior of clay, revealing and explaining the evolution pattern of clay pore structure during one-dimensional compression in terms of platelet alignment adjustment. This macroscopic compression is characterized by variations in pore size distribution, orientation, and aspect ratio.

Pore structure characteristics of coral reef limestone: a combined polarizing microscope and CT scanning study

Coral reef limestone is a special class of geological medium formed through long-term deposition following the death of reef-building coral groups. Because it retains the skeletal structure of marine organisms during its formation, its pore structure is hyper-developed and complex. Deciphering the pore structure of the coral reef limestone is important because it is closely related to its macroscopic physical and mechanical properties. This study conducted a comprehensive analysis of the pore structure features of two types of coral reef limestone collected from the construction site of a nuclear power station located in the South China Sea using a combination of polarizing microscopy and CT scanning technologies. The fractal dimension of the pore structure of the treated reef limestone image was calculated, and the pore structure characteristics were statistically analyzed by considering several parameters including porosity, pore size, pore equivalent radius, shape factor, etc. In addition, the directional feature of the pore structure was explored. The results show that the improved watershed segmentation algorithm can accurately segment the pore structure of reef limestone images; both coral reef limestone specimens are loose of high porosity; the fractal dimension of pore structure lay between 1.58∼1.75, indicative of a high self-similarity; the pore size of the two coral reef limestone specimens is quite different, and the distribution of equivalent pore radius conforms to the normal distribution law; the pore structure of the two samples had obvious directionality, which can be quantified using a directional tensor. This study sheds light on future investigations linking the microscopic structure and macroscopic properties of coral reef limestones.

Fluorite-structured high-entropy oxide sputtered thin films from bixbyite target

The prototype high-entropy oxide (HEO) Y0.2La0.2Ce0.2Pr0.2Sm0.2O2−δ represents a particularly complex class of HEOs with significant anion sublattice entropy. The system takes either a fluorite or bixbyite-type crystal structure, depending on synthesis kinetics and thermal history. Here, we synthesize bulk ceramics and epitaxial thin films of Y0.2La0.2Ce0.2Pr0.2Sm0.2O2−δ and use diffraction to explore crystal symmetry and phase. Thin films exhibit the high symmetry fluorite phase, while bulk ceramics adopt the lower symmetry bixbyite phase. The difference in chemical ordering and observed symmetry between vapor-deposited and reactively sintered specimens suggests that synthesis kinetics can influence accessible local atomic configurations, i.e., the high kinetic energy adatoms quench in a higher-effective temperature, and thus higher symmetry structure with more configurational entropy. More generally, this demonstration shows that recovered HEO specimens can exhibit appreciably different local configurations depending on synthesis kinetics, with potential ramifications on macroscopic physical properties.

Formations of force network and softening of amorphous elastic materials from a coarsen-grained particle model

Amorphous materials, such as granular substances, glasses, emulsions, foams, and cells, play significant roles in various aspects of daily life, serving as building materials, plastics, food products, and agricultural items. Understanding the mechanical response of these materials to external forces is crucial for comprehending their deformation, toughness, and stiffness. Despite the recognition of the formation of force networks within amorphous materials, the mechanisms behind their formation and their impact on macroscopic physical properties remain elusive. In this study, we employ a coarse-grained particle model to investigate the mechanical response, wherein local physical properties are integrated into the softness of the particles. Our findings reveal the emergence of a chain-like force distribution, which correlates with the planar distribution of softness and heterogeneous density variations. Additionally, we observe that the amorphous material undergoes softening due to the heterogeneous distribution of softness, a phenomenon explicable through a simple theoretical framework. Moreover, we demonstrate that the ambiguity regarding the size ratio of the blob to the force network can be adjusted by the amplitude of planar fluctuations in softness, underscoring the robustness of the coarse-grained particle model.

Study on the effect of wood admixture on the physical and mechanical properties of corn cob ecological recycled concrete

This paper investigates the physical and mechanical properties of ecological concrete using corn cob pellets, shavings, and wood chips. Wood chips and shavings were partially used as substitutes for corn cob particles to enhance the physical and mechanical properties of the eco-concrete. The impact of substitution on the macroscopic physical and mechanical properties is examined based on various pore structures. The pore size distribution was analyzed using the non-destructive testing technique of nuclear magnetic resonance (NMR). The pore complexity is analyzed through fractal dimension analysis. The pore distribution was assessed using magnetic resonance imaging (MRI). The roughness of pore distribution was analyzed by combining gray theory and counting the box dimension. The addition of biomass particles results in a 22-fold increase in the content of harmful pores, which can be quantitatively and visually observed using NMR and MRI techniques. This is the reason of compressive strength deterioration. Additionally, the optimal substitution of wood chips is determined. With a maximum biomass admixture of 50%, the uniaxial compressive strength increased by 18.9% (to 2.565 MPa, which meets the strength requirements of self-bearing wall insulation blocks). This study aims to establish a foundation for utilizing ecological concrete in agricultural facilities and rural wall materials.

Pore structure characterization of sandstone under different water invasion cycles using micro-CT

The meso-structural changes of rocks during repeated cycles of water invasion are the fundamental cause of macroscopic physical property damage. In this paper, based on the computed tomography scan images of rock samples under different numbers of water invasion cycles, a three-dimensional pore network model was constructed to analyze the changes in pore structure under the action of water invasion. The damage variable was introduced to quantitatively characterize the parameter damage of each pore and reveal the evolution of rock meso-damage. The results show that 81% of the pore radius is less than 10 μm under 0 water invasion cycles and that 76% of the pore radiuses are less than 10 μm after 10 water invasion cycles. After 10 water invasion cycles, the peak range of the pore radius distribution enlarged from the initial range of 2–4 μm to that of 4–6 μm and the proportion of pore throats with a radius less than 10 μm decreased from an initial 82–72%. With an increase of water invasion cycles, the proportion of large pores increased and the connectivity among pores enhances gradually. The damage variable of each pore parameter changed the most during 2–5 water invasion cycles. After 10 water invasion cycles, the maximum degree of damage that the pore volume reached was up to 41.44% and the minimum degree of damage of the pore coordination number was 5.80%. The test results helped to reveal the pore structure changes and the damage of rock samples during water invasion cycles.

Experimental Study on the Morphology of Snow Crystal Particles and Its Influence on Compacted Snow Hardness

In their natural state, snow crystals are influenced by the atmosphere during formation and multiple factors after landing, resulting in varying particle sizes and unstable particle morphologies that are challenging to quantify. The current research mainly focuses on the relationship between the porosity of compacted snow samples or qualitatively describes snow crystals and their macroscopic physical properties, ignoring that the significant differences in the morphology of snow crystals also affect their physical properties. To quantitatively evaluate the morphology of snow crystals, we employed optical microscopy to obtain digital images of snow crystals in Harbin, utilizing the Sobel and Otsu algorithms to determine the equivalent particle size and fractal dimension of individual snow particles. In addition, the hardness of snow with a density of 0.4 g/cm3 was measured through a penetration test, with an analysis of its correlation relative to particle size and fractal dimension. The results indicated the fractal dimension as an effective parameter for characterizing particle shape, which decreased rapidly over time and then fluctuated within the range of 1.10 to 1.15. During the initial period, natural snow crystals broke down rapidly, leading to an increase in the percentage of natural snow crystals with an equivalent particle size of 0.2–0.4 mm up to 51.86%. After three days, the sintering effect between snow crystals was enhanced, resulting in an even distribution of the equivalent particle size. Finally, multiple linear regression analysis showed a positive correlation between compacted snow hardness and fractal dimension, with a negative correlation between compacted snow hardness and equivalent particle size. These findings offer valuable technical support and data reference for exploring the relationship between snow’s mechanical properties and its microscopic particle shape.

In-situ positron annihilation spectroscopy during tensile tests on Al alloys

We present a materials analysis method to enable in-situ Doppler broadening spectroscopy (DBS) of the 511 keV annihilation line in matter during tensile tests. This technique allows the correlation between the formation of lattice defects on an atomic scale and the macroscopic physical materials properties stress and strain. By implanting a monoenergetic positron beam into samples of AlMg3 (3.3535) and AlMgSi (3.3206) the onset of plastic deformation was clearly observed in the recorded annihilation spectra during the measurement of the corresponding stress–strain curves. The changes of the DBS spectra are attributed to positron annihilation in (open-volume) defects—predominantly vacancies elastically bound to dislocation lines—formed during plastic deformation. The elastic strain (Hook’s region), however, does not lead to changes in DBS spectra.

Research on the electronic phase transitions in strongly correlated oxides and multi-field regulation

External-field-triggered multiple electronic phase transitions within correlated oxides open up a new paradigm to explore exotic physical functionalities and new quantum transitions via regulating the electron correlations and the interplay in the degrees of freedom, which makes the multidisciplinary fields have the promising application prospects, such as neuromorphic computing, magnetoelectric coupling, smart windows, bio-sensing, and energy conversion. This review presents a comprehensive picture of regulating the electronic phase transitions for correlated oxides via multi-field covering the VO<sub>2</sub> and <i>Re</i>NiO<sub>3</sub>, thus highlighting the critical role of external field in exploring the exotic physical property and designing new quantum states. Beyond conventional semiconductors, the complex interplay in the charge, lattice, orbital and spin degrees of freedom within correlated oxides triggers abundant correlated physical functionalities that are rather susceptible to the external field. For example, hydrogen-related electron-doping Mottronics makes it possible to discover new electronic phase and magnetic ground states in the hydrogen-related phase diagram of correlated oxides. In addition, filling-controlled Mottronics by using hydrogenation triggers multiple orbital reconfigurations for correlated oxides away from the correlated electronic ground state that results in new quantum transitions via directly manipulating the d-orbital configuration and occupation, such as unconventional Ni-based superconductivity. The transition metals of correlated oxides are generally substituted by dopants to effectively adjust the electronic phase transitions via introducing the carrier doping and/or lattice strain. Imparting an interfacial strain to correlated oxides introduces an additional freedom to manipulate the electronic phase transition via distorting the lattice framework, owing to the interplay between charge and lattice degrees of freedom. In recent years, the polarization field associated with BiFeO<sub>3</sub> or PMN-PT material triggered by a cross-plane electric field has been used to adjust the electronic phase transition of correlated oxides that enriches the promising correlated electronic devices. The exotic physical phenomenon as discovered in the correlated oxides originates from the non-equilibrium states that are triggered by imparting external fields. Nevertheless, the underneath mechanism as associated with the regulation in the electronic phase transitions of correlated oxides is still in a long-standing puzzle, owing to the strong correlation effect. As a representative case, hydrogen-associated Mottronic transition introduces an additional ion degree of freedom into the correlated oxides that is rather difficult to decouple from the correlated system. In addition, from the perspective of material synthesis, the above-mentioned correlated oxides are expected to be compatible with conventional semiconducting process, by which the prototypical correlated electronic devices can be largely developed. The key point that accurately adjusts and designs the electronic phase transitions for correlated oxides via external fields is presented to clarify the basic relationship between the microscopic degrees of freedom and macroscopic correlated physical properties. On the basis, the multiple electronic phase transitions as triggered by external field within correlated oxides provide new guidance for designing new functionality and interdisciplinary device applications.

Study on the mechanical properties of granite responses of cyclic heating and water cooling considering microcosmic and energy.

Investigating the coupling effects of temperature levels and heating-water cooling cycles on the physical and mechanical responses of HDR (hot dry rock) is a vital issue during the exploitation of geothermal energy. In this study, the physical properties of granite specimens were measured first after each heating and water-cooling cycle. Then, uniaxial compressive tests were conducted on those granites to obtain their mechanical properties. With the increase in heating temperature (T) and cycles of heating and water cooling (N), P-wave velocity, uniaxial compression strength (UCS), and elastic modulus (E) showed a decreasing tendency, and the decrease of those four properties corresponding to T variation is greater than N variation. Due to the α-β phase transition of quartz happening at 573°C, the density UCS and E of granite decreased rapidly when the heating temperature increased from 450°C to 600°C at N = 1. With the increase of T and N, the failure mode of granite gradually changes from tensile failure to shear failure and, finally, comminute failure. The failure mechanism of granite gradually transfers from brittleness-dominated to ductility-dominated due to accumulated thermal damage. Finally, X-ray diffraction (XRD) and scanning electron microscope (SEM) were used to determine the damage mechanism of cyclic heating-cooling. The micro test results show that the high-temperature treatment changes the mineral composition and the microcracks number of the granite and finally affects the macroscopic physical and mechanical properties. The study conclusions of this manuscript are important for exploiting geothermal resources.

Molecular machines working at interfaces: physics, chemistry, evolution and nanoarchitectonics.

As a post-nanotechnology concept, nanoarchitectonics combines nanotechnology with advanced materials science. Molecular machines made by assembling molecular units and their organizational bodies are also products of nanoarchitectonics. They can be regarded as the smallest functional materials. Originally, studies on molecular machines analyzed the average properties of objects dispersed in solution by spectroscopic methods. Researchers' playgrounds partially shifted to solid interfaces, because high-resolution observation of molecular machines is usually done on solid interfaces under high vacuum and cryogenic conditions. Additionally, to ensure the practical applicability of molecular machines, operation under ambient conditions is necessary. The latter conditions are met in dynamic interfacial environments such as the surface of water at room temperature. According to these backgrounds, this review summarizes the trends of molecular machines that continue to evolve under the concept of nanoarchitectonics in interfacial environments. Some recent examples of molecular machines in solution are briefly introduced first, which is followed by an overview of studies of molecular machines and similar supramolecular structures in various interfacial environments. The interfacial environments are classified into (i) solid interfaces, (ii) liquid interfaces, and (iii) various material and biological interfaces. Molecular machines are expanding their activities from the static environment of a solid interface to the more dynamic environment of a liquid interface. Molecular machines change their field of activity while maintaining their basic functions and induce the accumulation of individual molecular machines into macroscopic physical properties molecular machines through macroscopic mechanical motions can be employed to control molecular machines. Moreover, research on molecular machines is not limited to solid and liquid interfaces; interfaces with living organisms are also crucial.

Investigation on permeability of filter cake with different particle sizes: Experimental and simulation study

Cake permeability is a crucial macroscopic physical property in characterizing filtration behavior for coal slurry. However, there is still no appropriate model derived to establish the essential relationship between the cake permeability and complex particle property. In this study, the three-dimensional microstructures with different particle gradation and porosity were generated using particle discrete element software. The permeability of each constructed model was calculated utilizing Lattice Boltzmann Method (LBM). Simulation result shows that the Kozeny–Carman (KC) model is proper to predict the permeability of porous media with different gradations. When the gradation parameters are not considered, it shows that d30 can best represent the particle size characteristics of the particle systems. When the porosity and average particle size remain unchanged, the permeability increases with the increasing of the non-uniformity coefficient (Cu) and the curvature coefficient (Cc). Moreover, we proposed an analytical expression for the permeability estimation with different gradation characteristics, which contains the parameters that can be easily measured in engineering. Then a set of coal slurry samples with different particle size distributions were selected to conduct the filtration test, the permeability of each sample was measured to compare with the predicted results of the gradation permeability model. It is clear that the KC equation in this case can not calculate the cake permeability effectively. Although the gradation model is relatively appropriate to estimate the cake permeability, its accuracy still needs to be improved by considering the pore structure property to eliminate the effect of constant terms.

Experimental investigations on the physico-mechanical and microstructural properties of loess reinforced with anionic polyacrylamide

The typical characteristics of loess, such as macropores, weak cementation, and strong collapsibility, can adversely affect the stability of building foundations, transportation infrastructure, and other geotechnical systems. To address this problem, a water-soluble anionic polyacrylamide (APAM) was used to improve the characteristics of loess. A series of multi-scale geotechnical engineering tests, such as sedimentation column, zeta potential, Atterberg limits, standard compaction, permeability, triaxial compression strength, scanning electron microscope (SEM), nuclear magnetic resonance (NMR), and X-ray diffraction (XRD) tests were conducted on the loess samples. The results showed that the APAM polymer could flocculate fine loess particles into stable agglomerates via a series of physical actions, including charge neutralization, adsorption and bridging, and hydrophobic interactions. The contact form among the loess particles changed from loose point contact to strong mosaic contact with the addition of the APAM polymer, the surface porosity, fractal dimension, and interplanar spacing of the treatment material decreased significantly. The considerable improvement of loess microstructure affected its macroscopic physical and mechanical properties. The optimum moisture content and permeability coefficient of the treated loess decreased with the increases of the APAM content, whereas the plasticity index and maximum dry density increased. Additionally, the failure strength of the loess samples first increased then decreased as the APAM content increased, which showed the maximum value at an addition amount of 0.30% content, beyond which its strength value decreased. The test results demonstrated that the APAM polymer treatment could provide significant improvement in the macroscopic physico-mechanical and microstructural properties of loess. This study will serve as a crucial resource for loess foundation stabilization using the environmentally friendly and cost-effective polymer.