Loose State Research Articles

Electrical resistivity of iron ore mine tailings produced in Western Australia

This paper presents the details of an experimental study on the electrical resistivity of iron ore mine tailings produced in Western Australia. In the study, an experimental set-up is developed based on the Wenner Array, and has been used for determining the electrical resistivity of the tailings at different relative densities in dry and fully saturated conditions. The apparent electrical resistivity of the iron ore mine tailings ranged from 11 kΩm for a very dense state to 19 kΩm for a very loose state in dry condition; while for the fully saturated condition, the resistivity ranged from 20 to 31 Ωm for very dense state to very loose state, respectively. The results are discussed for their practical applications such as identifying weak zones in tailing embankments, extent of corrosion in buried steel pipelines, and extent of degree of compaction in structural fills.

A constitutive model for the state-dependent behaviors of rockfill material considering particle breakage

The particle breakage during specimen compaction had more significant influence on the position of the breakage critical-state line (BCSL) of Tacheng rockfill material (TRM) in the e-lnp′ plane than the particle breakage during shearing, based on the large-scale triaxial compression tests on TRM in a wide range of densities and pressures. The state-dependent dilatancy and the plastic modulus were correlated to the breakage index, based on the formulations of the BCSL of TRM in the e-lnp′ plane. The state-dependent model considering particle breakage was proposed for TRM within the framework of the generalized plasticity theory. The proposed model contained fourteen material constants. The test data of TRM from Group A were adopted to determine these material constants, while the test data from Group B were used independently to validate the model predictive capacity. The comparisons between model simulations and test data illustrated that the model with consideration of particle breakage could well represent the stress-strain behaviors of TRM, e.g., the strain hardening and volumetric contraction behaviors at a loose state and the strain softening and volumetric expansion behaviors at a dense state, and also the particle breakage behaviors of TRM.

Insight into the Effects of Gradation on the Pore Pressure Generation of Sand–Silt Mixtures

Liquefaction of saturated sandy soils has been considered as the main cause of most geotechnical hazards during earthquakes. Generation of excess pore water pressures in saturated silty sands when subjected to monotonic, cyclic, and earthquake loading has been shown to cause the liquefaction, which can be defined as the transformation of stable soil structure into unstable liquid form. The proposed research investigated the effect of grading characteristics on the generated excess pore water pressure of sand–silt mixture samples in loose, medium dense, and dense states. The laboratory investigation aimed at understanding the extent or degree at which excess pore pressure of sand–silt mixture soil is affected by its gradation under static loading conditions. For the purpose of clarifying and evaluating the generated pore pressure characteristics of sandy soils, a series of undrained monotonic triaxial tests were carried out on different reconstituted samples of sand–silt mixtures with various gradations. The soil samples were tested under a constant confining pressure (σ3′ = 100 kPa) and at three relative densities (Dr = 20 %, 53 %, and 91 %). The results from this laboratory investigation were used to develop insight into the pore water pressure response of sand and sand–silt mixtures under monotonic loading conditions. The analysis of the obtained data revealed that the grading characteristics [D10, D50, Cu, effective size ratio (ESR), and mean grain size ratio (MGSR)] have significant influence on the generation of the excess pore water pressure. It was found that maximum positive excess pore water pressure (Δumax) can be correlated to the grading characteristics for the sand–silt mixture. The ESR and MGSR appear as pertinent parameters to predict the excess pore water pressure response of the sand–silt mixtures for soil gradation under study.

Discrete element modeling of shear band in granular materials

Numerical biaxial tests using discrete element method (DEM) were carried out to study the shear band formation in granular materials and the microstructures of the specimen at different strain levels were carefully examined. The effect of initial density and confining pressure on the characteristics of shear band were investigated. It was found that the progressive formation of the shear band was successfully captured by the DEM simulation with flexible lateral boundaries. During the shearing, several potential shear bands are formed at the peak deviatoric shear stress. With further shearing, the potential shear bands enlarge and softening behavior happens. Finally, a persistent shear band forms and other potential shear bands deteriorate. Generally, loose state and high confining pressure “delay” the onset of shear banding. The simulation also showed that the shear band thickness decreases with increasing confining pressure and density. Meanwhile, the inclination angle of shear band in dense specimen is generally higher than that in loose specimen. The void ratio of shear band is significantly larger than other parts of the specimen. At microscopic level, the overall coordination number of the specimen decreases significantly. The coordination number in the shear band is significantly lower than that outside the shear band, which is consistent with the large porosity in the shear band. The formation of shear band is due to the bulking of lateral confining force chains and the shear band is characterized by large void ratio, low coordination number, and high particle sliding and rotation compared with other part of the specimen.

A novel manifold–manifold distance index applied to looseness state assessment of viscoelastic sandwich structures

Viscoelastic sandwich structures (VSS) are widely used in mechanical equipment; their state assessment is necessary to detect structural states and to keep equipment running with high reliability. This paper proposes a novel manifold–manifold distance-based assessment (M2DBA) method for assessing the looseness state in VSSs. In the M2DBA method, a manifold–manifold distance is viewed as a health index. To design the index, response signals from the structure are firstly acquired by condition monitoring technology and a Hankel matrix is constructed by using the response signals to describe state patterns of the VSS. Thereafter, a subspace analysis method, that is, principal component analysis (PCA), is performed to extract the condition subspace hidden in the Hankel matrix. From the subspace, pattern changes in dynamic structural properties are characterized. Further, a Grassmann manifold (GM) is formed by organizing a set of subspaces. The manifold is mapped to a reproducing kernel Hilbert space (RKHS), where support vector data description (SVDD) is used to model the manifold as a hypersphere. Finally, a health index is defined as the cosine of the angle between the hypersphere centers corresponding to the structural baseline state and the looseness state. The defined health index contains similarity information existing in the two structural states, so structural looseness states can be effectively identified. Moreover, the health index is derived by analysis of the global properties of subspace sets, which is different from traditional subspace analysis methods. The effectiveness of the health index for state assessment is validated by test data collected from a VSS subjected to different degrees of looseness. The results show that the health index is a very effective metric for detecting the occurrence and extension of structural looseness. Comparison results indicate that the defined index outperforms some existing state-of-the-art ones.

Studies on electrical resistivity of Perth sand

This paper presents experimental and numerical studies on electrical resistivity of Perth sand in its very loose state to very dense state. A simple laboratory experimental setup was developed to measure the electrical resistivity in terms of its apparent value, using the Wenner array of electrodes. The electrode spacing and depth were varied to investigate their influence on the resistivity values. The results indicate that an increase in electrode depth causes a decrease in resistivity, whereas an increase in electrode spacing results in an increase in resistivity for all the relative densities of sand. In view of limitations with respect to the geometry and electrode configuration of the laboratory setup, the values determined using the classical Wenner array expression ρ = 2πa(ΔV/I) (I = current, ΔV = potential difference, a = equal electrode spacing, and ρ = electrical resistivity) required corrections by a suitable factor. To determine this correction factor for a specific electrode arrangement, say electrode depth = 150 mm, electrode spacing = 180 mm, as an example, in our resistivity box, finite element (FE) simulation was carried out using the commercial software COMSOL. The simulation results indicate that a correction factor of about 0⋅46 should be applied to the value calculated using the expression in order to obtain more realistic values. By employing this methodology, it was found that the electrical resistivity of dry Perth sand ranged from 60 606 Ω m for the very dense state to 142 857 Ω m for the very loose state.

Bounding Surface Plasticity Model Incorporating the State Pressure Index for Rockfill Materials

AbstractThe critical state line of Tacheng rockfill material (TRM) was described by a pressure-power function. A simple bounding-surface plasticity model, combining the dilatancy stress ratio and peak-failure stress ratio pertaining to the state pressure index, was developed for TRM within the framework of critical-state soil mechanics and the bounding surface plasticity. Detailed investigations of influences of design parameters on the model predictions were carried out. The developed model, using a set of model constants, captured well behaviors such as strain hardening and volumetric contraction for TRM in a loose state (e.g., at a large initial void ratio or a high initial confining pressure) and strain softening and volumetric expansion in a dense state (e.g., at a small initial void ratio or a low initial confining pressure).

On estimation of the constriction size distribution curve for cohesionless soils

Internal stability against suffusion and filter efficiency are two important issues in geotechnical engineering. To well assess them, the constriction size distribution (CSD) of soil particles must be determined accurately. Both the Silveira model and the modified Silveira model have been widely used to mathematically simulate CSD curves and then to simulate filtration process in filters, for example. In the Silveira model, it was assumed that the constrictions are formed among groups of four soil particles at the loosest state, while the constrictions are assumed to be formed among four particles at any relative density in the modified model. We took a close look at the models and found that some groups of the possible four soil particles were not taken into account. As a result, the number of groups computed in the models is fewer than the number of actual unique groups. To demonstrate the effect of this difference on model prediction, we obtained the CSD curves using numerical and experimental tests and compared these curves with those predicted using the modified Silveira model and the Silveira model. Our comparison indicated that this difference has a significant effect on the CSD results using the modified Silveira model while it has a negligible impact on those calculated using the Silveira model. For the former, proper fitting factors are needed to have an accurate prediction of the CSD curves.

A sequential fuzzy diagnosis method for rotating machinery using ant colony optimization and possibility theory

This study proposes a novel intelligent fault diagnosis method for rotating machinery using ant colony optimization (ACO) and possibility theory. The non-dimensional symptom parameters (NSPs) in the frequency domain are defined to reflect the features of the vibration signals measured in each state. A sensitive evaluation method for selecting good symptom parameters using principal component analysis (PCA) is proposed for detecting and distinguishing faults in rotating machinery. By using ACO clustering algorithm, the synthesizing symptom parameters (SSP) for condition diagnosis are obtained. A fuzzy diagnosis method using sequential inference and possibility theory is also proposed, by which the conditions of the machinery can be identified sequentially. Lastly, the proposed method is compared with a conventional neural networks (NN) method. Practical examples of diagnosis for a V-belt driving equipment used in a centrifugal fan are provided to verify the effectiveness of the proposed method. The results verify that the faults that often occur in V-belt driving equipment, such as a pulley defect state, a belt defect state and a belt looseness state, are effectively identified by the proposed method, while these faults are difficult to detect using conventional NN.

Effects of density on cyclic behaviour of anisotropically consolidated Ottawa sand under undrained torsional loading

The undrained response of Ottawa sand to cyclic torsional loading in a hollow cylinder apparatus is assessed at various densities. The cyclic resistance of Ottawa sand is strongly affected by anisotropic consolidation. It is less than half of the cyclic strength of isotropically consolidated material at the loose state; this trend reverses at the dense state. Cyclic strength resistance increases with density irrespective of consolidation path. Anisotropically consolidated specimens develop at all densities a terminal excess pore-water pressure which is less than 40% of the initial effective stress, and fail due to strain rather than pore-water pressure accumulation, contrary to isotropically consolidated specimens reaching pore pressure ratios higher than 70%. The development of excess pore-water pressure is uniquely related to the shear work imparted to the specimen; at the same excess pore-water pressure ratio shear work increases with density, whereas it is not affected by the applied cyclic shear stress amplitude. The phase transformation line is not affected by the consolidation path and appears to be the same under monotonic and cyclic loading conditions.

Aberrant histone acetylation contributes to elevated interleukin-6 production in rheumatoid arthritis synovial fibroblasts

Accumulating evidence indicates that epigenetic aberrations have a role in the pathogenesis of rheumatoid arthritis (RA). However, reports on histone modifications are as yet quite limited in RA. Interleukin (IL)-6 is an inflammatory cytokine which is known to be involved in the pathogenesis of RA. Here we report the role of histone modifications in elevated IL-6 production in RA synovial fibroblasts (SFs). The level of histone H3 acetylation (H3ac) in the IL-6 promoter was significantly higher in RASFs than osteoarthritis (OA) SFs. This suggests that chromatin structure is in an open or loose state in the IL-6 promoter in RASFs. Furthermore, curcumin, a histone acetyltransferase (HAT) inhibitor, significantly reduced the level of H3ac in the IL-6 promoter, as well as IL-6 mRNA expression and IL-6 protein secretion by RASFs. Taken together, it is suggested that hyperacetylation of histone H3 in the IL-6 promoter induces the increase in IL-6 production by RASFs and thereby participates in the pathogenesis of RA.

Monolayer Behavior of Cyclic and Linear Forms of Surfactins: Thermodynamic Analysis of Langmuir Monolayers and AFM Study of Langmuir-Blodgett Monolayers

The molecular interactions of monolayers composed of cyclic and linear forms of surfactins (SFs) were evaluated through atomic force microscopy (AFM) together with a Langmuir monolayer technique. The surface pressure (π)-area per molecule (A) isotherm of a pure cyclic surfactin (CSF) monolayer exhibited a liquid expanded (Le) monolayer, while that of a pure linear surfactin (LSF) monolayer exhibited a liquid condensed (Lc) monolayer, demonstrating that the CSFs are in a rather loose molecular packing state owing to its bulky heptapeptide ring. The plots of the mean area per molecule of the CSF/LSF monolayers were well fitted to the ideal curves, suggesting that ideal mixing occurs, or that the two components are immiscible in a monolayer. The AFM images of the CSF/LSF monolayers transferred at 25 mN/m gave phase-separated microdomain structures, indicating that the CSFs and LSFs are almost immiscible and separated into a CSF-rich and LSF-rich phases, as suggested from the analysis of the mean area per molecule of the monolayers. Our results clearly demonstrated that the cleavage of the cyclic heptapeptide headgroup of CSF drastically changes its molecular packing state in a monolayer and that AFM observation combined with the Langmuir monolayer technique is quite useful to explore the manner of self-assembly of a binary system of microbial products such as CSFs and LSFs.

Undrained cyclic shear strength of crushable sands

Because of their lightweight and highly crushable and compressible nature, pumiceous sands are problematic from engineering and construction viewpoints. There has been very little information on their liquefaction characteristics, and most empirical procedures available in evaluating the liquefaction potential of sands are derived primarily from hard-grained sands. To understand the undrained cyclic behavior of pumice sands, several series of undrained cyclic triaxial tests were performed on two sets of pumice samples. One set of samples consisted of undisturbed pumiceous deposits taken from a site in Waikato, whereas the other set involved reconstituted pumice sands in both loose and dense states. The results obtained were compared with those observed in Toyoura sand, a typical (hard-grained) sand. The degree of particle breakage in pumice during cyclic shearing was examined, highlighting the effect of the crushable nature of the grains on the cyclic response of the soil.

A Self-Sequestered Calmodulin-like Ca2+ Sensor of Mitochondrial SCaMC Carrier and Its Implication to Ca2+-Dependent ATP-Mg/Pi Transport

The mitochondrial carriers play essential roles in energy metabolism. The short Ca²⁺-binding mitochondrial carrier (SCaMC) transports ATP-Mg in exchange for Pi and is important for activities that depend on adenine nucleotides. SCaMC adopts, in addition to the transmembrane domain (TMD) that transports solutes, an extramembrane N-terminal domain (NTD) that regulates solute transport in a Ca²⁺-dependent manner. Crystal structure of the Ca²⁺-bound NTD reveals a compact architecture in which the functional EF hands are sequestered by an endogenous helical segment. Nuclear magnetic resonance (NMR) relaxation rates indicated that removal of Ca²⁺ from NTD results in a major conformational switch from the rigid and compact Ca²⁺-bound state to the dynamic and loose apo state. Finally, we showed using surface plasmon resonance and NMR titration experiments that free apo NTDs could specifically interact with liposome-incorporated TMD, but that Ca²⁺ binding drastically weakened the interaction. Our results together provide a molecular explanation for Ca²⁺-dependent ATP-Mg flux in mitochondria.

Stability Control of Continuous Compaction Measurement in High-Speed Railway Subgrade

The compaction stability is of great significant for the quality control and assurance of the continuous compaction measurement in subgrade engineering. Based on the mean-variation method, the exponential function between the roller passes and the roller measurement value was modeled to calculate the compaction stability index Δμtmv. The stabilization process of the compacted soil from loose state to dense state could be well described by the modeled function. Through the results of the roller measurement values in three test field of Shanghai-kunming high-speed rail in Huaihua, Zhijiang and Loudi, different compaction stability index due to the varied construction situations was calculated using the mean-variation method and the exponential function. The result shows that the exponential function is well adaptive to different situations and this method could be developed in controlling the stability of continuous compaction measurement.

Survey of Chromites Fields Adjacent Rocks Loosening in Case of Their Uncontrolled Caving

Control and regulation of the formation behavior while using the uncontrolled caving method require thorough investigation of the formation properties and structure, its geological, geostructural and geotechnical parameters as well as geomechanical peculiarities of rock pressure generation and its effect in the course of ore deposits mining.The most indicative are the mining plants of Donskoy Mining and Concentration Complex, which operate the uncontrolled caving method for mining of thick ore deposits at the chromite ore fields.The fields of South-Kem pirsay chromite-bearing block are the second largest fields comparing to Republic of South Africa and Zimbabwe. Prospectivity and extent of the operations at the fields could be described by the rate of production and its development: Molodyozhnaya mine of 2.0 million tons annual output is the world largest underground mining of chromite ore.Currently mining of ore deposits at Donskoy chromites fields is carried out at rather significant depths (of 500 and more meters), the second working of subjacent strata is carried out as well.Along with the extension of second working areas under the specified conditions, carrying out of the large-scale development operations and pre-production development as well as generation of closed extraction mines, there is the necessity to ensure more rational regulation of the rock pressure, provision for safe structural components of the mining system, selection of the methods and means for mine workings fixing and, finally, provision of efficient and reliable system of ore deposits mining. In applying this system it is critical to determine the caving zone sizes, which could be calculated quite easily depending on the ore body parameters, direction and sequence of its reserves development, whereas its height would depend on the extent of the increase of the caving rock block volume due to its loosening. This article outlines the results of laboratory tests on determination of the volume of loose rocks, which is calculated on the basis of the loosening factor (kр) that represents the ...ratio of the rock volume in loose (bulk) state to its volume as the solid block….

Time-Resolved Magnetic Field Effects Distinguish Loose Ion Pairs from Exciplexes

We describe the experimental investigation of time-resolved magnetic field effects in exciplex-forming organic donor–acceptor systems. In these systems, the photoexcited acceptor state is predominantly deactivated by bimolecular electron transfer reactions (yielding radical ion pairs) or by direct exciplex formation. The delayed fluorescence emitted by the exciplex is magnetosensitive if the reaction pathway involves loose radical ion pair states. This magnetic field effect results from the coherent interconversion between the electronic singlet and triplet radical ion pair states as described by the radical pair mechanism. By monitoring the changes in the exciplex luminescence intensity when applying external magnetic fields, details of the reaction mechanism can be elucidated. In this work we present results obtained with the fluorophore-quencher pair 9,10-dimethylanthracene/N,N-dimethylaniline (DMA) in solvents of systematically varied permittivity. A simple theoretical model is introduced that allows discriminating the initial state of quenching, viz., the loose ion pair and the exciplex, based on the time-resolved magnetic field effect. The approach is validated by applying it to the isotopologous fluorophore-quencher pairs pyrene/DMA and pyrene-d10/DMA. We detect that both the exciplex and the radical ion pair are formed during the initial quenching stage. Upon increasing the solvent polarity, the relative importance of the distant electron transfer quenching increases. However, even in comparably polar media, the exciplex pathway remains remarkably significant. We discuss our results in relation to recent findings on the involvement of exciplexes in photoinduced electron transfer reactions.

Strength Improvement of Loose Sandy Soils Through Cement Grouting

Grouting, which has several applications in the field of civil engineering, was once considered as a mysterious operation. The effectiveness of grouting requires a lot of understanding, skill, meticulous attention and an intuitive perception. Even though grouting was started 200 years ago, it was treated for a long time, as an art which eluded scientific investigation and improvement. Grout is injected under pressure into the material to be grouted until it fills the desired volume of material around the hole or until the maximum specified pressure is attained and a specific minimum grout flow is reached. This paper discusses the strength improvement of loose sandy soils through cement grouting. Various cement percentages (2, 4 and 6 %) were used for grouting medium sand beds in the loosest state. The effectiveness of grouting was evaluated based on the actual cross sectional area of the intact grouted mass at different depths and by determination of cement content at various depths and laterals distances of the grouted medium. The improvement in strength due to grouting was assessed with the help of load tests. 4 % cement grout was found to be more effective in medium sand compared to 2 and 6 %. The results undoubtedly prove the effectiveness of using grouting as an efficient technique in improving the foundation beds of loose sandy soils.

A Dilatancy Constitutive Modelling of Saturated Sands Based on the State Parameter

A bounding-surface model is modified and introduced a state parameterbased on phase transformation state, e.g., when subjected to shear, sand will contract until phase transformation is reached, while, then dilatant until the ultimate where =constants simultaneously. With state parameter the deformation tendency of a sand at any time or any conditions can be judged correctly. As a result the dilatancy depends on the state in a way that yields a zero value at phase transformation state. This dependence allows a realistic modelling of the response of a sand in either loose or dense state, or in the transition from one state to another state. A comparison between model simulations and a sequence of experimental results for drained, monotonic loading conditions shows that the proposed concept and modelling technique work effectively using a unique set of parameters (or parameter dependence) for a given sand.

Lattice-strain effect on oxygen vacancy formation in gadolinium-doped ceria

By first-principles calculations using the projector-augmented-wave (PAW) method, the oxygen vacancy formation energy of gadolinium-doped ceria (GDC) is calculated as a function of lattice strain comprising the range from compressive (−1.5 %) to dilative (1.5 %) strain. Employing the generalized gradient approximation (GGA) for the exchange correlation potential and including the strong on-site Coulombic repulsion U, the calculations are performed within the (GGA) + U formalism. For simplicity of interpretation, all calculations are carried out based on the assumption that structural relaxation in GDC occurred under isotropic strain states. According to the calculation of the energetics of vacancy formation, the formation energy shows the lowest value at dilative strain conditions, where the lattice structure is in the loosest state. Furthermore, the generated oxygen vacancy has a preferred migration path that is mainly controlled by the neighboring cation configuration.