Slip line theory applied to a retaining wall–unsaturated soil interaction problem

An extension of slip line theory to unsaturated soils is presented and applied to the problem of a rigid retaining wall rotating about its toe into unsaturated soils. Suction is introduced using the effective stress concept. Soil–wall interface friction is defined carefully. The influence of suction on limiting passive earth pressures is analysed for two soils under steady state evaporation and infiltration. Suction increases the limiting passive stress at the soil–wall interface, with a dependence on the steady state flow type. The displacement of the retained soil is studied assuming the wall undergoes a rotation increment. The results show a clear difference in the displacement for evaporation and infiltration.     

Metal contamination of surface sediments of the Sfax–Chebba coastal line,Tunisia

Concentrations of several heavy metals (Pb, Cr, Cd, Cu, Zn and Fe) in surface sediment were determined to investigate the distributions and the metallic pollution status in Sfax–Chebba coastal area (southeast of Tunisia). Sediment samples were collected from 20 locations, representing three different site groups (i.e., site I: urban zone, site II: pre-urban zone and site III: rural zone). Heavy metal contents were analyzed by Atomic Absorption Spectrometry. The obtained results showed that generally, heavy metal concentrations in the coastal sediments near Sfax city (urban zone) were higher than those at other stations because of the anthropogenic activities. These concentrations exceeded the threshold effect levels. This was confirmed by the chemometric approaches (enrichment factors, geoaccumulation index and principal component analysis) which showed a significant impact of multiple anthropogenic sources. Moderate to extremely severe enrichment of sediments in terms of Pb, Cr, Cd, Cu and Zn were shown to exist in site I. Severe enrichment by Cd was also observed in other sites. Based on the geoaccumulation index, Pb, Cr, Cd, Cu and Zn can be considered as unpollutants to extreme pollutants.     

Numerical analyses of uplift behavior of pile foundation for transmission line structure in frozen soil regions北大核心CSCD

Pile foundation is one of the most commonly used and suitable foundations to support transmission line structure, especially in seasonally frozen soil regions and permafrost regions. Axial compression is the controlling condition in the design of foundations for such structures as bridges and buildings, while uplift and overturning will control the design of transmission line structure foundations. This paper presents an extensive overview of previous studies including experimental (e. g., laboratory model test and full-scale field load test), analytical/theoretical (e. g., limit equilibrium and limit analysis based on plasticity)and numerical(e. g., finite difference and finite element methods). The review indicates that study on the uplift behavior of pile foundation in frozen soil is relatively limited, particularly in the case of combined effect of axial uplift and lateral loading. Interaction between pile and frozen soil and mechanism of load transfer along the pile shaft and around the pile tip still remain unclear. Therefore, this paper implements finite difference analysis within FLAC3D to investigate the behavior of pile foundation in frozen silty clay and gravelly sand under axial uplift behavior and the effect of ground condition and lateral loading on the uplift behavior. Because of the axisymmetric condition of the problem studied, only half of the model is simulated. The chosen domain of the medium is discretized into a set of quadrilateral elements and the pile is discretized by the cylinder element. The interaction between the soil and pile is considered according to interface elements. Mohr-Coulomb criterion is adopted to model the soil behavior (perfectly elastic-plastic), while the pile is simply considered as a rigid body. The soil parameters such as Young’s modulus, cohesion and internal friction angle used for numerical analyses are determined by laboratory tests and estimated according to the empirical correlations with in-situ tests. The present numerical modeling is verified with the results from field loading tests on pile foundations in Qinghai-Tibet ±550 kV transmission line project. On this basis, parametric studies are carried out to uncover the behavior of pile in frozen soil. It is observed that pullout is the dominant failure mechanism of pile and the uplift load-displacement curve clearly exhibits an asymptote, consisting of initially linear elastic, nonlinear transition, and finally linear regions. These results are consistent with the observations in a few previous studies. In addition, larger uplift capacity of pile foundation in freezing period and gravelly sand is gained (about 20%). Lateral loading increases the deflection and therefore, decreases the uplift capacity of pile foundation. For the convenience of using the results obtained in practice, the values of uplift factor for pile foundation in silty clay and gravelly sand are provided. Finally, it should be noted that the method used, and the results obtained in the current work could be useful for engineers and designers, at least providing them some qualitative evidence for pile design in seasonally frozen soil regions and permafrost regions. This is important and necessary to ensure the safety of construction in such regions. Meanwhile, numerical analyses in the current work can be a benchmark example for subsequent research studies. © 2022 Science Press (China).     

Liquid line of descent of a basanitic liquid at 1.5 Gpa: constraints on the formation of metasomatic veins

The metasomatism observed in the oceanic and continental lithosphere is generally interpreted to represent a continuous differentiation process forming anhydrous and hydrous veins plus a cryptic enrichment in the surrounding peridotite. In order to constrain the mechanisms of vein formation and potentially clarify the nature and origin of the initial metasomatic agent, we performed a series of high-pressure experiments simulating the liquid line of descent of a basanitic magma differentiating within continental or mature oceanic lithosphere. This series of experiments has been conducted in an end-loaded piston cylinder apparatus starting from an initial hydrous ne-normative basanite at 1.5 GPa and temperature varying between 1,250 and 980°C. Near-pure fractional crystallization process was achieved in a stepwise manner in 30°C temperature steps and starting compositions corresponding to the liquid composition of the previous, higher-temperature glass composition. Liquids evolve progressively from basanite to peralkaline, aluminum-rich compositions without significant SiO₂ variation. The resulting cumulates are characterized by an anhydrous clinopyroxene + olivine assemblage at high temperature (1,250–1,160°C), while at lower temperature (1,130–980°C), hydrous cumulates with dominantly amphibole + minor clinopyroxene, spinel, ilmenite, titanomagnetite and apatite (1,130–980°C) are formed. This new data set supports the interpretation that anhydrous and hydrous metasomatic veins could be produced during continuous differentiation processes of primary, hydrous alkaline magmas at high pressure. However, the comparison between the cumulates generated by the fractional crystallization from an initial ne-normative liquid or from hy-normative initial compositions (hawaiite or picrobasalt) indicates that for all hydrous liquids, the different phases formed upon differentiation are mostly similar even though the proportions of hydrous versus anhydrous minerals could vary significantly. This suggests that the formation of amphibole-bearing metasomatic veins observed in the lithospheric mantle could be linked to the differentiation of initial liquids ranging from ne-normative to hy-normative in composition. The present study does not resolve the question whether the metasomatism observed in lithospheric mantle is a precursor or a consequence of alkaline magmatism; however, it confirms that the percolation and differentiation of a liquid produced by a low degree of partial melting of a source similar or slightly more enriched than depleted MORB mantle could generate hydrous metasomatic veins interpreted as a potential source for alkaline magmatism by various authors.     

Solar flare-related eruptions followed by long-lasting occultation of the emission in the He II 304 ? line and in microwaves

Plasma with a temperature close to the chromospheric one is ejected in solar eruptions. Such plasma can occult some part of emission of compact sources in active regions as well as quiet solar areas. Absorption phenomena can be observed in the microwave range as the so-called “negative bursts” and also in the He II 304 ? line. The paper considers three eruptive events associated with rather powerful flares. Parameters of absorbing material of an eruption are estimated from multi-frequency records of a “negative burst” in one event. “Destruction” of an eruptive filament and its dispersion like a cloud over a huge area observed as a giant depression of the 304 ? line emission has been revealed in a few events. One of the three currently known events is considered in this paper. One more of the events considered here is a possible candidate for such events.     

Thermodynamic mixing behavior of synthetic Ca-Tschermak–diopside pyroxene solid solutions: III. An analysis of IR line broadening and heat of mixing behavior

A series of synthetic Ca-Tschermak–diopside (CaAlAlSiO₆–CaMgSi₂O₆) clinopyroxenes were investigated by powder infrared spectroscopy at room temperature in the wavenumber range 80–2,000 cm⁻¹. Measurable local structural heterogeneities in the crystals are suggested by the line broadening parameter, Δcorr that are observed for intermediate solid-solution compositions. The broadening is most pronounced in the high wavenumber region of the IR spectra that contains stretching modes involving the TO₄ polyhedra. The effective line widths for three selected wavenumber regions deviate positively from linear behavior. This is also observed for the enthalpy of mixing of this solid solution. The relationship between “excess Δcorr”, δΔcorr, and heat of mixing, ΔH _mix, behavior was investigated for this clinopyroxene series and for several other binary silicate solid solutions. The ΔH _mix versus δΔcorr slope values show a linear relationship with respect to the integrated excess volume of the various solid solutions.     

Filaments and the underlying surface from He I and H<Emphasis Type="Italic">α</Emphasis> line observations

Bright bands are observed along filaments in the He I 1083 nm line, while both bright and dark bands are observed along Hα 656.3 nm filaments. The range of brightness variations near He I filaments is 1.005–1.10 times the unperturbed brightness, with an average of 1.031 ± 0.01, while this range is 0.91–1.5 times the unperturbed brightness for Hα filaments. The physical state of the matter in these bands is investigated. Computations of the band brightness have been carried out for various chromospheric models, aimed at explaining the observed features of the bands. Two types of models are considered: with temperature or density variations in the upper chromosphere, and with temperature variations in the middle and lower chromosphere. In the first type of model, the brightness in the He I line is changed, but the Hα brightness is not. In the second type of model, only the Hα brightness is changed. Using the variations of the chromospheric parameters and both types of models, we obtained various combinations of band brightnesses in the He I line and in Hα. The brightnesses of regions were estimated by calculating the profiles of the He I and Hα lines in the corresponding models in a non-LTE approximation. A comparison of the observed and calculated quantities indicates that the enhancement in the brightness in the He I line is due to a decrease in temperature or density in the upper chromosphere (where the temperatures are about 10 000–24 000 K). The enhancement and dimming of the brightness in Hα are due to an increase or decrease of the temperature in the middle and lower chromosphere (where the temperatures are 6000–9000 K) by 800–1000 K. The dependence of the band brightness on distance from the center of the solar disk is also considered. The brightness in the He I line increases from the center to the limb by 2–4%. Computations of the center–limb brightness variaions correspond to the observed results.     

Impact of data assimilation in simulation of thunderstorm (squall line) event over Bangladesh using WRF model,during SAARC–STORM Pilot Field Experiment 2011

Natural Hazards - A widespread thunderstorm (squall line or multicell line) occurred over Bangladesh on 11 May 2011 during 0300 UTC to 1300 UTC. A north–south oriented well-established squall...     

Seismic, gravity, and wire line logging characterization of the Zéramdine fault corridor and its influence in the deep Miocene aquifers distribution (east-central Tunisia)

In the Jemmel?CZéramdine region, the combined analysis of petroleum well data, seismic reflection profiles, and gravity data show the presence of the Zéramdine fault corridor, which was activated in the Neogene period. Both tectonic activity and fluvio-deltaic sedimentation are the origin of the lithologic and hydrodynamic heterogeneities. Thus, the Zéramdine fault corridor constitutes a limit between two hydraulic systems formed by Miocene sandy reservoir layers. These reservoirs have not been exploited yet and could be new water resources which can extremely benefit the region; only the upper one is exploited in the Jemmel?CBembla and Zéramdine?CBéni Hassen deep aquifers. The wire line logging, seismic reflection, and gravity interpretations show the distribution of the Miocene layers which formed the Sahel Miocene deep aquifers. The Zéramdine fault corridor leads to a spatial variability in number, distribution, depths, and thicknesses of these reservoir layers. In the northern part of the Zéramdine fault corridor, seven layers were highlighted; their thicknesses range between 15 and 105?m. However, in the southern part, only four strata were deposited: their thicknesses vary between 45 and 53?m. The total porosity of the studied aquifers is about 30%.     

Redefining the watershed line and stream networks via digital resources and topographic map using GIS and remote sensing (case study: the Neka River’s watershed)

The accurate delineation of area plays a key role in the surveying of land change detection and the classification of land covers. In a hydrologic system, the watershed delineation and the detection of the boundaries among watershed is a basic method for performing spatial analyses. After recent advances in image processing and raster-based spatial analysis in geographic information systems, and being easily accessible data via various sources especially through remote sensing, the reliable determination of topographical boundaries possible is possible. Therefore, an integrated approach of data analysis and modeling can accomplish the task of delineation. The main aim in this research is to evaluate the delineation method of watershed boundary using four different digital elevation models (DEM) including advanced spaceborne thermal emission and reflection radiometer (ASTER), Shuttle Radar Topographic Mission (SRTM), digital topography, and topographic maps. In order to determine a true reference of boundary of watershed, sample data were also obtained by field survey and using global positioning system (GPS). The comparison reference points and the results of these data showed the average distance difference between reference boundary, and the result of ASTER data was 43 m. However, the average distance between GPS reference and the other data was high; the difference between the reference data and SRTM was 307 m, and for digital topographic map, it was 269 m. The average distance between topographic map and the GPS points differed 304 m as well. For the statistical analysis of comparison, the coordinates of 230 points were determined; the paired comparisons were also performed to measure the coefficient of determination, R ², as well as analysis of variance in SPSS software. As a result, the R ² values for the ASTER data with the digital topography and topographic map were 0.0157 and 0.171, respectively. The results showed that there were statistically significant differences in distances among the four means of the selected models. Therefore, considering other three methods, the ASTER DEM is the most suitable applicable data to delineate the borders of watersheds, especially in rugged terrains. In addition, the calculated flow directions of stream based on ASTER are close to natural tributaries as well as real positions of streams.     

Synthetic light curves of close binaries in a cool-disk model. The “hot line” and “hot spot” as visual indicators of interaction between the flow and disk

We present a “combined” model taking into account visual manifestations of the interaction between the gas flow and the accretion disk in a close binary system in the form of a “hot line” and a “hot spot.” The binary consists of a red dwarf that fills its Roche lobe and a compact spherical star (a white dwarf or neutron star) surrounded with a thick ellipsoidal accretion disk of a complex shape. The disk thickness is not large near the compact star but increases according to a parabolic law towards its outer edge. The oblique collision of the gaseous flow with matter of the cool, rotating disk, whose outer edge has a temperature <10 000 K, creates an extended region of enhanced energy release. In the combined model, this region is represented with a hot line that coincides with the optically opaque part of the flow and is located outside the disk, together with a hot spot at the outer surface of the disk, on the leeward side of the flow. The synthetic light curves for the combinedmodel and a hot-line model demonstrate that both models are able to fairly accurately reproduce the shapes of both classical and atypical light curves of cataclysmic variables in quiescence. Our determination of the parameters of the cataclysmic variable OY Car from an analysis of its light curves using the two models shows that the basic characteristics of the close binary, such as the component mass ratio q = M ₁/M ₂, orbital inclination i, effective temperatures of the red dwarf (T ₂) and white dwarf (T ₁), and orientation of the disk α _e , remain the same within the errors. The parameters describing the size of the slightly elliptical disk and the radiation flux from the disk differ by several percent (∼ 2–8%). A more significant difference is detected in the parameters of the hot line, due to the different shape and alignment of the flow and the presence of an additional radiation source—the hot spot—on the disk.     

Analytical approximation for the Fe <Emphasis Type="Italic">K</Emphasis><Subscript>α</Subscript> emission line in quasar spectra

The spectra of many Seyfert galaxies display broad Fe K _α emission. The line profile has two maxima, suggesting that the line emerges in the innermost regions of an accretion disk around a black hole, making it necessary to take into account general relativistic (GR) effects. Identifying GR processes occuring in active galactic nuclei (AGN) requires reconstructing the parameters of the accreting system from the line profile using some reasonably quick algorithm. We present here a numerical approximation for the Fe K _α emission line using analytical functions. The approximation encompasses a range of the disk radial coordinate r and the angle θ between the line of sight and the disk normal, and makes it possible to decrease the computing time by six orders of magnitude in certain astrophysical problems, while taking into account all GR effects. Results of the approximation are available at http://www.iki.rssi.ru/people/repin/approx.