Laboratory Investigation of the Effect of Initial Dry Density and Grain Size Distribution on Soil–Water Characteristic Curves of Wide-Grading Gravelly Soil

Wide-grading gravelly soils are often encountered in debris flow source areas. To perform stability analyses under rainfall conditions, the soil–water characteristic curves (SWCC) are significant. However, the studies for SWCC of wide-grading gravelly soils are rare. In order to investigate the effects of initial dry density and grain size distribution on the SWCCs of wide-grading gravelly, a large-scale osmotic column, allowing the measurement of both volumetric water content and matric suction at various levels, was fabricated for a series of osmotic column tests. The test data were best-fitted to Van Genuchten equation using a least-squares algorithm and found that both the initial dry density and grain size distribution had a greater effect on the SWCCs. An increase in the initial dry density resulted in an increase in water retention capacity. The air entry value and residual volumetric water content increased linearly with increases in the initial dry density, whereas the maximum slope of SWCC decreased linearly with increases in the initial dry density. The air entry value and residual volumetric water content increased linearly with increases in the fine content (particle diameter <0.075), whereas the maximum slope increases linearly with increases in the effective size, d ₁₀.     

Experimental Characterization of the Shrinkage and Water Retention Behaviour of Tailings from Hard Rock Mines

Mining of hard rock ore deposits produces large amounts of tailings. The safe disposal and management of these tailings require an extensive characterization that should include their drying and desaturation behaviour. Desiccation tests have been performed to characterize the shrinkage response of low plasticity tailings having an initially loose state. The testing procedure developed for this purpose is briefly described here. The main shrinkage tests results are then presented. The experimental data are compared with those obtained from water retention tests performed in a pressure plate with volume change measurements. These two types of results are combined to define unsaturated (drying and shrinkage) relationships in six complementary planes that include the volumetric shrinkage curve and the water retention curve. Specific material characteristics are then determined, including the shrinkage limit w _S, final void ratio e _f, and air entry value ψ _a. Additional tests were also performed to define critical parameters at the initiation of cracking in terms of suction ψ, water content w, and degree of saturation S _r. The original results presented here indicate that the onset of desaturation is closely linked with the end of volumetric straining and with crack initiation. Results also show that the shrinkage limit w _S is a function of the specimen initial water content w ₀. Other related characteristics are also presented and discussed.     

Evaporation,shrinkage and intrinsic permeability of unsaturated clayey soil: analytical modelling versus experimental data

This paper presents the experimental study conducted on a clayey soil originating from the region of Béja, north-west of Tunisia. The evaporation, shrinkage and permeability behaviours were studied. The Soil Water Retention Curve (SWRC) was determined from the slurry state to dry state, under the desiccation path (called initial drying curve). The Crack Intensity Factor (CIF), settlement and void ratio were also studied to characterise the shrinkage phenomenon during desiccation. Moisture content (ω), saturation degree (S_r) and evaporation rate (R_e) evolutions during desiccation path were also presented. This type of slurry clay presents three stages during the desiccation process (pendular, funicular and capillary regimes). During desiccation process, the evaporation rate presents a linear relationship as a saturation degree function. Furthermore, the evaporation rate versus suction presents two phases: quasi-saturated and unsaturated states. This paper introduces a study of the hygroscopic and mechanical parameters naturally modified during a desiccation process and proposes some analytical models to describe clay behaviour. Using these parameters, we can determine the intrinsic permeability during the desiccation process.     

Permeability of granular soil employing flexible wall permeameter

Understanding the changes in permeability of soil, when soil is subjected to high confining pressure and flow pressure, which may alter the textural and geomechanical characteristics of soil, is of great importance to many geo-engineering activities such as, construction of high-rise buildings near the coast or the water bodies, earthen dams, pavement subgrades, reservoir, and shallow repositories. It is now possible to evaluate the changes in permeability of soil samples under varying conditions of confining pressure and flow pressure using flexible wall permeameter (FWP). In the present study, investigation was carried out on a cylindrical sample of granular soil employing FWP under varied conditions of confining pressure (σ₃)—50–300 kPa, which can simulate the stress conditions equivalent to depth of about 20 m under the earth’s crust, and a flow pressure (f_p)—20–120 kPa, which is mainly present near the small earthen embankment dams, landfill liners, and slurry walls near the soft granular soil with high groundwater table. The obtained results indicate a linear relationship between hydraulic conductivity (k) with effective confining pressure (σ_eff.), k, decreasing linearly with an incremental change in σ_eff.. Further, k increases significantly with an increase in f_p corresponding to each σ_eff., and q increases significantly with increase in the f_p corresponding to each (σ₃). It was also observed that corresponding to the low f_p of 20 kPa, the reduction in k is nonlinear with σ_3. The percentage reduction in k is observed to be 9, 13, and 27% corresponding to σ₃ of 50–100, 100–200, and 200-300 kPa, respectively.     

Stability and phase relations of nonstoichiometric clinopyroxenes in the join diopside-Ca-Eskola component at high pressures

The stability of nonstoichiometric clinopyroxenes in the Di-CaEsk join was experimentally studied, and phase diagrams were constructed for this join at pressures of 2.0 and 3.0 GPa. It was found that melting in the diopside part of the join occurs at anomalously low temperatures, and nonstoichiometric clinopyroxene coexists with a phase approaching diopside in composition. Phase relations along the Di-CaEsk join can be described and consistently interpreted only assuming that the diopside phase (α-diopside) is thermodynamically stable. The following phase volumes were observed along the solidus of the join at a pressure of 3.0 GPa: Cpx, αDi+Cpx, αDi+Cpx+Qtz, αDi+Cpx+Grt+Qtz, Cpx+Grt+Qtz, Cpx+Grt+Ky+Qtz, Grt+Ky+Qtz. Melting occurs via the eutectic reaction αDi+Cpx+Grt+Qtz=L at a temperature of about 1200°C in the diopside part of the system and via the eutectic reaction Cpx+Grt+Ky+Qtz=L at a temperature of 1400°C in the calcium-rich part of the system. At a pressure of 2.0 GPa, melting occurs at temperatures of 1200–1300°C via the eutectic reaction αDi+Cpx+ An + Qtz=L. The invariant equilibrium (L, An, Cpx, Grt, αDi, Qtz) lies within the pressure range 2.0–3.0 GPa. Nonstoichiometric clinopyroxenes form complex solid solutions, the compositions of which are not strictly confined to the Di-CaEsk join and depend on temperature, pressure, and phase association. Grossular garnets coexist with nonstoichiometric clinopyroxenes and α-diopside.     

MHD accretion of a perfect fluid with an ultrahard equation of state onto a moving Schwarzschild black hole

The full version of the magnetohydrodynamical (MHD) theory of accretion of a perfect fluid with an ultrahard equation of state, p = μ ~ ρ² (where p is the pressure, μ the total energy density, and ρ the fluid density), onto a moving Schwarzschild black hole is considered. Exact and approximate analytical solutions have been found. It is shown that smooth continuous solutions exist only in the case when a single critical sound surface is formed.     

Analysis of magnetic activity of the rapidly rotating stars He 373 and AP 225

Spectroscopic and photometric data for the two rapidly rotating members of the α Persei cluster He 373 and AP 225 are analyzed. Improved estimates have been obtained for the projected equatorial rotation velocities: v sin i = 164 km/s for He 323 and v sin i = 129 km/s for AP 225. Multi-band photometric mapping is used to map the spot distributions on the surfaces of the two stars. The fractional spotted areas S and mean temperature difference ΔT between the unspotted photosphere and the spots are estimated (S = 7% and ΔT = 1000 K for He 373; S = 9% and ΔT = 800 K for AP 225). The H _α line profiles of both stars have variable emission components whose widths are used to deduce the presence of extended regions of emission reaching the corotation radius.     

Pre-flare changes in the turbulence regime for the photospheric magnetic field in a solar active region

Observations of the total magnetic field in the active region NOAA 6757 have been used to study the turbulence regime from 2.5 h before the onset of a 2B/X1.5 flare until two minutes after its maximum. The curvature of the exponent ζ(q) for the structure functions of the B _z field increases monotonically before the flare (i.e., the multifractal character of the B _z field becomes more complex) but straightens at the flare maximum and coincides with a linear Kolmogorov dependence (implying a monofractal structure for the B _z field). The observed deviations of ζ(q) from a Kolmogorov line can be used for short-term forecasting of strong flares. Analysis of the power spectra of the B _z field and the dissipation of magnetic-energy fluctuations shows that the beginning of the flare is associated with the onset of a new turbulence regime, which is closer to a classical Kolmogorov regime. The scaling parameter (cancellation index) of the current helicity of the magnetic field, k _h , remains at a high level right up until the last recording of the field just before the flare but decreases considerably at the flare maximum. The variations detected in the statistical characteristics of the turbulence can be explained by the formation and amplification of small-scale flux tubes with strong fields before the flare. The dissipation of magnetic energy before the flare is primarily due to reconnection at tangential discontinuities of the field, while the dissipation after the flare maximum is due to the anomalous plasma resistance. Thus, the flare represents an avalanche dissipation of tangential discontinuities.     

Analytical expressions for three-phase generalized relative permeabilities in water- and oil-wet capillary tubes

We analyze three-phase flow of immiscible fluids taking place within an elementary capillary tube with circular cross-section under water- and oil-wet conditions. We account explicitly for momentum transfer between the moving phases, which leads to the phenomenon of viscous coupling, by imposing continuity of velocity and shear stress at fluid-fluid interfaces. The macroscopic flow model which describes the system at the Darcy scale includes three-phase effective relative permeabilities, K _{i j,r} , accounting for the flux of the ith phase due to the presence of the jth phase. These effective parameters strongly depend on phase saturations, fluid viscosities, and wettability of the solid matrix. In the considered flow setting, K _{i j,r} reduce to a set of nine scalar quantities, K _{i j,r} . Our results show that K _{i j,r} of the wetting phase is a function only of the fluid phase own saturation. Otherwise, K _{i j,r} of the non-wetting phase depends on the saturation of all fluids in the system and on oil and water viscosities. Viscous coupling effects (encapsulated in K _{i j,r} with i ≠ j) can be significantly relevant in both water- and oil-wet systems. Wettability conditions influence oil flow at a rate that increases linearly with viscosity ratio between oil and water phases.     

Microflora from sauropod coprolites and associated sediments of Late Cretaceous (Maastrichtian) Lameta Formation of Nand-Dongargaon basin,Maharashtra

Micofloral study of Lameta sediments and associated sauropod coprolites in the Nand-Dongargaon basin in Maharashtra was conducted to understand the diet and habitat of sauropods. The study revealed the presence of pollen, spores, algal and fungal remains, well-preserved cuticles of Poaceae, and testate amoebae. Vegetation during Lameta included tall arboreal taxa, such as conifers (Podocarpus and Araucaria), Cycads (Cycas), Euphorian and Barringtonia and herbs and shrubs, such as Cheirolepidiaceae (Classopollis), Arecaceae (Palmaepollenites), Poaceae (Graminidites), Asteraceae (Compositoipollenites), Caryophyllaceae (Cretacaeiporites and Periporopollenites), and Acanthaceae (Multiareolites). Data suggest that the sauropods ate soft tissues of angiosperms and gymnosperms. The intake of testate amoeba, algal remains, sponge spicules, and diatoms might be through water intake.     

Influence of physico-chemical components on the consolidation behavior of soft kaolinites

Pore solution salinity has important bearing on engineering behavior of marine sediments as they influence electrochemical stress (A–R) and differential osmotic stress (?π) of the salt-enriched clays. The electrochemical stress (A–R) is contributed by van der Waals (A) attraction and diffuse ion layer repulsion (R), while the differential osmotic stress (?π) is governed by the differences in dissolved salt concentrations in solutions separated by osmotic membrane. The paper examines the relative influence of differential osmotic stress (Δπ) and electrochemical stress (A–R) on the consolidation behavior of slurry consolidated kaolinite specimens, which are known to be encountered in recent alluvial marine sediments. Methods are described to evaluate the magnitudes of these physico-chemical components and their incorporation in true effective stress. Results of the study demonstrate that differential osmotic stress finitely contributes to true effective stress. The contribution from differential osmotic stress enables kaolinite specimens to sustain larger void ratio during consolidation.     

Prevalence of pathogenic microorganisms and their correlation with the abundance of indicator organisms in riverbed sediments

The present study investigated the prevalence of pathogenic organisms (Salmonella spp, Vibrio cholerae, and Shigella spp) and their correlation to the abundance of faecal indicator organisms in water and riverbed sediments in the Apies River, South Africa. In all, 558 water and sediment samples were collected from 10 sites in the river (May 2013–February 2014) and analysed through culture and molecular (real-time PCR) techniques. Concentrations of faecal indicator organisms in sediments reached 1.39 × 10⁵ (±standard deviation) CFU/100 mL. All three pathogens were detected in water and sediments. Pathogens were mostly detected in sediments at sites influenced either by wastewater treatment works or by informal settlements. During the wet and dry seasons (water column), a strong positive correlation was observed between E. coli and all pathogens; C. perfringens only correlated with V. cholerae. Within sediments, strong positive correlations were only observed between E. coli and Salmonella spp, E. coli and V. cholerae (dry season); E. coli and V. cholerae and E. coli and Shigella spp (wet season). No correlation was observed between sediments C. perfringens counts and all the pathogens. Thus, sediments of the Apies River harbour pathogenic organisms. Correlation between E. coli and pathogenic organisms in the sediments suggests that E. coli could also be an indicator of pathogens’ presence. However, the lack of a correlation between E. coli and some pathogens in sediments and between C. perfringens and all the pathogens highlights the need to investigate for more indicators of pathogens’ presence in this complex matrix.     

Sand-supported bio-adsorbent column of activated carbon for removal of coliform bacteria and <Emphasis Type="Italic">Escherichia coli</Emphasis> from water

New bio-adsorbent carbon materials were synthesized from the leaves and veins of Mucuna pruriens and Manihot esculenta plants, which are locally available in abundance. The synthesized carbons were activated using 0.01N HNO₃. Surface area of the activated carbons from M. pruriens and M. esculenta plants was found to be quite high, i.e., 918 and 865 m²/g, respectively. Scanning electron microscopy analysis of the carbons reflects complex disorganized surface structures of different open pore sizes, shapes and dimensions. These properties of the newly synthesized activated carbons led to the development of a sand-supported carbon column, for its possible use in the removal of coliform bacteria and Escherichia coli (E. Coli) from raw water samples. The removal percentage of E. coli was found to be 100% with both the types of carbon adsorbents, as confirmed from the McCardy most probable number table. Similarly, the removal percentage of coliform bacteria was found to be 99 and 98.7% by M. pruriens and M. esculenta carbon columns, respectively. These activated carbons synthesized from locally available plants possess the characteristics of good low-cost adsorbents which can be easily used for the removal of bacteria from water by adsorption method.     

Salinity Tolerance and Competition Drive Distributions of Native and Invasive Submerged Aquatic Vegetation in the Upper San Francisco Estuary

Both abiotic and biotic factors govern distributions of estuarine vegetation, and experiments can reveal effects of these drivers under current and future conditions. In upper San Francisco Estuary (SFE), increased salinity could result from sea level rise, levee failure, or water management. We used mesocosms to test salinity effects on, as well as competition between, the native Stuckenia pectinata (sago pondweed) and invasive Egeria densa (Brazilian waterweed), species with overlapping distributions at the freshwater transition in SFE. Grown alone at a salinity of 5, E. densa decreased fivefold in biomass relative to the freshwater treatment and decomposed within 3 weeks at higher salinities. In contrast, S. pectinata biomass accumulated greatly (~4× initial) at salinities of 0 and 5, doubled at 10, and was unchanged at 15. When grown together in freshwater, S. pectinata produced 75 % less biomass than in monoculture and significantly more nodal roots (suggesting increased nutrient foraging). At a salinity of 5, a decline in E. densa performance coincided with a doubling of S. pectinata shoot density. Additional experiments on E. densa showed elevated temperature (26 and 30 °C) suppressed growth especially at higher salinities (≥5). We conclude that salinity strongly influences distributions of both species and that competition from E. densa may impose limits on S. pectinata abundance in the fresher reaches of SFE. With a salinity increase of 5, S. pectinata is likely to maintain its current distribution while spreading up-estuary at the expense of E. densa, especially if increased temperature also reduces E. densa biomass.     

Direct numerical simulation of a turbulent stably stratified air flow above a wavy water surface

The influence of the roughness of the underlaying water surface on turbulence is studied in a stably stratified boundary layer (SSBL). Direct numerical simulation (DNS) is conducted at various Reynolds (Re) and Richardson (Ri) numbers and the wave steepness ka. It is shown that, at constant Re, the stationary turbulent regime is set in at Ri below the threshold value Ri_c depending on Re. At Ri > Ri_c, in the absence of turbulent fluctuations near the wave water surface, three-dimensional quasiperiodical structures are identified and their threshold of origin depends on the steepness of the surface wave on the water surface. This regime is called a wave pumping regime. The formation of three-dimensional structures is explained by the development of parametric instability of the disturbances induced by the surface water in the air flow. The DNS results are quite consistent with prediction of the theoretical model of the SSBL flow, in which solutions for the disturbances of the fields of velocity and temperature in the wave pumping regime are found to be a solution of a two-dimensional linearized system with the heterogeneous boundary condition, which is caused by the presence of the surface wave. In addition to the turbulent fluctuations, the three-dimensional structures in the wave pumping regime provide for the transfer of impulse and heat, i.e., the increase in the roughness of the water–air boundary caused by the presence of waves intensifies the exchange in the SSBL.     

Planktic foraminiferal biostratigraphy of the Maastrichtian-Paleocene succession at the north Farafra Oasis,Western Desert,Egypt

Seven planktic foraminiferal zones are distinguished in the Maastrichtian-Paleocene succession at the north Farafra Oasis. These are the Rugoglobigerina hexacamerata (CF8b), Gansserina gansseri, and Contusotruncana contusa zones in the Maastrichtian topped by a well-known unconformity across the Cretaceous/Paleogene (K/Pg) boundary. The Danian is subdivided into two biozones: Globanomalina compressa/Praemurica inconstans-Praemurica uncinata Subzone (P1c) and Praemurica uncinata–Morozovella angulata (P2) Zone. The Late Paleocene is divided into two zones: Morozovella angulata-Globanomalina pseudomenardii (P3) and Globanomalina pseudomenardii (P4). A minor hiatus between the Danian/Selandian and Selandian/Thanetian boundaries are also recorded. These time gaps across the stage boundaries may be related to the tectonic events that affected the sedimentation regime throughout the Upper Cretaceous–Lower Paleogene interval in the Farafra Oasis.     

Fractionation of Rare-Earth Elements in the Processes of Hydrothermal Ore Formation

The data on the distribution of elements in the Pb–Zn cross-section of the Gatsirovskaya vein (the Upper Zgid deposit, North Ossetia, Russia) have shown that the spectra of rare-earth elements (REEs) changed significantly in the ore samples during the vein formation. The sharp growth of the La_N/Yb_N, La_N/Nd_N, Gd_N/Ho_N, and Gd_N/Yb_N ratios is confined to the vein intervals, where the maximum amount of ore components is deposited. The comparison of the REE spectra of ores to the characteristics of the spectra of the rocks surrounding the vein and the host rocks suggests that the vein material deposited from the solutions in which the REE ratio changed with time. REE fractionation occurred due to the mobilization of components by hydrothermal solutions during their interaction with the Paleozoic host granites.     

Impact of pore water conductivity and porosity on the electrical conductivity of kaolinite

The purpose of this study is to quantify the magnitudes of surface conduction and pore water conduction from the measured electrical conductivity of kaolinite, with the ultimate goal of estimating the electrical conductivity of kaolinite with a wide range of pore water conductivities (σ _w = 0.013–3.356 S/m) and porosities (n = 0.368–1.0). Therefore, the theoretical background of the electrical conductivity in soils was reviewed, and electrical conductivity measurements on kaolinite were performed using both slurry and consolidation tests in this study. The results of this study demonstrate that the variations of measured electrical conductivity (σ _mix) with n are debatable according to the values of σ _w, because a decrease in n results in both an increase in surface conduction (K _s) and a decrease in pore water conduction (K _w); this causes the relative magnitude of K _s compared to that of K _w to vary with σ _w and n. Consequently, this study develops the relation between the porosity-normalized K _s/K _w and 1/σ _w. Additionally, the surface conductivity of the tested kaolinite is back-calculated and compared with the previous relationship between K _s and zeta potential of kaolinite. The measured and estimated σ _mix values are compared with the varying pore water conductivity and porosity values.     

Short- and Long-Term Vegetative Propagation of Two <Emphasis Type="Italic">Spartina</Emphasis> Species on a Salt Marsh in Southern Brazil

Spartina alterniflora and Spartina densiflora are native salt marsh plants from the Atlantic coast; their habitats in Patos Lagoon estuary (southern Brazil) are characterized by a microtidal regime (<0.5 m) and, during El Niño events, high estuarine water levels and prolonged flooding due to elevated freshwater discharge from a 200,000-km² watershed. During and between El Niño events, the vegetative propagation of these two Spartina species in the largest estuary of southern Brazil (Patos Lagoon) was evaluated by monitoring transplanted plants for 10 years (short-term study) and interpreting aerial photos of natural stands for 56 years (long-term study). During the short-term study, S. alterniflora quickly occupied mud flats (up to 208 cm year^?1) by elongation of rhizomes, whereas S. densiflora showed a modest lateral spread (up to 13 cm year^?1) and generated dense circular-shaped stands. However, moderate and strong El Niño events can promote excessive flooding and positive anomalies in the estuarine water level that reduce the lateral spread and competitive ability of S. densiflora. During the long-term study, natural stands of S. alterniflora and S. densiflora had steady lateral spread rates of 152 and 5.2 cm year^?1, respectively, over mud flats. In the microtidal marshes of the southwest Atlantic, the continuous long-term lateral expansion of both Spartina species embodies periods of intense flooding stress (moderate and strong El Niños), when there is a decrease of vegetative propagation and less stressful low water periods of fast spread over mud flats (non-El Niño periods and weak intensity El Niños).