Using chemical analysis and modeling to enhance the understanding of soil solution of some calcareous soils

The chemistry of soil solutions can be altered by human activities, due to the intense agricultural and husbandry, leading to leaching of nutrients and subsequently elevating ground water levels. Multivariate statistical and inverse geochemical modeling techniques were used to determine the main factors controlling soil solution chemistry of calcareous soils. In this research, a total of 21 calcareous soils was characterized and assessed for soil solution using soil column. The major cations in the studied soil solutions were in the decreasing order as Ca²⁺ > Mg²⁺ > Na⁺ > K⁺. The anions were also arranged in decreasing order as HCO $ _{3}^{ - } $  > Cl $ ^{ - } $  > SO $ _{4}^{2 - } $  > NO $ _{3}^{ - } $ . Concentrations of NO $ _{3}^{ - } $ , P, and K⁺ in soil solutions were in the range of 6.8–307.5 mg l^?1 (mean 63.2 mg l^?1), 5.0–10.4 mg l^?1 (mean 5.9 mg l^?1), and 2.8–54.6 mg l^?1 (mean 11.3 mg l^?1), respectively. Results suggest that the concentration of P in the soil solutions could be primarily controlled by the solubility of dicalcium phosphate dihydrate and dicalcium phosphate. Interactions between soil properties and observed solubility of nutrients were described, and put into empirical multivariate formulations. Obtained equations contained electrical conductivity (EC) as a key factor in determining nutrients solubility. Inverse geochemical modeling of soil solution using PHREEQC indicates the dissolution of calcite, anhydrite, halite, CO₂ (g), N₂ (g), and hydroxyapatite, and precipitation of sulfur. Cation exchange between Ca²⁺, Mg²⁺, K⁺ and Na⁺ occurred with Mg²⁺ and K⁺ into the solution, and Ca²⁺ and Na⁺ out of the solution. Determination of soil solution will improve soil management in the area, and preventing groundwater deterioration.     

Mapping of the soil texture using geostatistical method (a case study of the Shahrekord plain, central Iran)

Soil texture is a key variable that reflect a number of soil properties such as soil permeability, water holding capacity, nutrient storage and availability, and soil erosion. The main objective of this study was to produce the kriged maps of soils of the Shahrekord region, central Iran. One hundred four soil samples were collected on a 375-m² sampling grid from the depths of 0–30, 30–60, and 60–100 centimeter, and their particle sizes were determined using hydrometer method. The results showed a moderately spatial correlation in the soil particles among sampling soil layers and across the study area. Moreover, increasing clay and therewith observation of heavier soil textures is evident from surface to subsurface layers of the soils in the studied area due to rainfall and/or irrigation agriculture. These findings indicated that study of the soil texture variation with depth can be used as a clue for site-specific management and precision agriculture. Moreover, we suggest further analysis by using other data layers like topographical parameters, land use, parent material, soil erosion, and any other information which might influence the spatial distribution of soil texture.     

Applicability of fiber reinforced self-compacting concrete for tunnel lining

Nowadays, self-compacting concrete is used in reinforced concrete structure with heavy bars. This type of concrete is widely accepted throughout the world; therefore, it can be used as an attractive solution for inner lining of tunnels. Regarding the effect of fibers in improving the concrete properties the effect of using polypropylene fiber on the behavior of arch specimens are investigated in laboratory. Therefore, specimens with dimensions of 1 m diameter, 0.5 m width, and 10 cm thickness with various reinforcing bars in arch forms were prepared and their flexural strength was investigated. The results show high ability of self-compacting concrete for the inner coverage of tunnels and its increasing strength is due to use of fibers. In addition, the results indicate that by adding fibers in the amount of 0.1 % of cement weight and reinforcing bars of size number 10, the required flexural strength would be obtained.     

Seismic assessment of concrete gravity dams using capacity estimation and damage indexes

A new concept to determine state of the damage in concrete gravity dams is introduced. The Pine Flat concrete gravity dam has been selected for the purpose of the analysis and its structural capacity, assuming no sliding plane and rigid foundation, has been estimated using the two well‐known methods: nonlinear static pushover (SPO) and incremental dynamic analysis (IDA). With the use of these two methods, performance and various limit states of the dam have been determined, and three damage indexes have been proposed on the basis of the comparison of seismic demands and the dam's capacity. It is concluded that the SPO and IDA can be effectively used to develop indexes for seismic performance evaluation and damage assessment of concrete gravity dams. Copyright © 2012 John Wiley & Sons, Ltd.     

Interaction of a Fresh Water Lake and a Karstic Spring via a Syncline Fold

Kaftar Lake is a high‐altitude fresh water lake located in High Zagros, south of Iran. Despite the high annual evaporation to precipitation ratio in the area, lake water electrical conductivity is usually lower than 1000 µS/cm, this may be due to high seepage from the floor of the lake. Therefore, the hypothesis of possible underground connections between Namdan Basin, where the lake is located, and the surrounding basins with lower elevation (Aspas and Dehbid Basins) was investigated. Hydrogeology, hydrochemistry, and stable isotopes data of the lake and surrounding basins along with the lake water balance study were applied to test the hypothesis. Results indicate that Kaftar Lake has no connection with Aspas Basin in south, but it is hydraulically connected to Dehbid Basin. In Dehbid Basin, “Ghasr_e_Yaghoob spring” (average discharge ?1200 L/s) emerges from a small outcrop (about 0.8 km²) of Daryan limestone Formation, where this outcrop is much smaller than the required recharge area for such average discharge rate. The study shows that this spring is recharged by Kaftar Lake and Namdan Basin aquifer, through Daryan Formation of Gandboee Syncline located to the northern part of the lake.     

Application of inverse geochemical modelling for predicting surface water chemistry in Ekbatan watershed,Hamedan, western Iran

ABSTRACT

A study of surface water chemistry evolution was conducted by multivariate statistical analysis and inverse geochemical modelling using the PHREEQC computer program. Using hierarchical cluster analysis the 14 sampling sites were classified into three groups (recharge, transition and discharge areas). Water chemistry changed along a flow path so that waters with Ca–HCO₃ and Mg–Cl composition changed to Mg–Cl–HCO₃ waters. The order of abundance of the major cations was Mg > Ca > Na > K. Their average concentrations were 21, 19, 3.6 and 2.5 mg L^-1, respectively. Inverse geochemical modelling along flow paths indicated that the dissolution of sylvite and kaolinite, and precipitation of feldspars and andalusite, happened with Na entering the solution and Ca, Mg and K leaving the solution.

Editor D. Koutsoyiannis; Associate editor not assigned     

Enhancement of Carbon Dioxide Capture by Amine‐Functionalized Multi‐Walled Carbon Nanotube

In this study, crude multi‐walled carbon nanotubes (MWCNT) was functionalized by a two‐step process; first using strong mixed acids (H₂SO₄/HNO₃) and then treatment with 1,3‐phenylenediamine (mPDA). The equilibrium adsorption of CO₂ on pristine MWCNT and amine functionalized MWCNT (MWCNT‐NH₂) were investigated. Experiments were preformed via application of volumetric method in a dual sorption vessel at temperature range of 298–318 K and pressures up to 40 bars. The results obtained indicated that the equilibrium uptake of CO₂ increased after functionalizing of MWCNT. The increase in CO₂ capture by MWCNT‐NH₂ was attributed to the existence of great affinity between CO₂ molecules and amine sites on this adsorbent at low pressures. The experimental data were analyzed by means of Freundlich and Langmuir adsorption isotherm models. The data obtained revealed a fast kinetics for the adsorption of CO₂ in which most of adsorption occurred at initial period of adsorption experiments. This renders MWCNT as a suitable adsorbent for practical applications. Values of isosteric heat of adsorption were evaluated based on Clausius–Clapeyron equation. The results demonstrated that both chemisorption and physisorption played important role in CO₂ adsorption on MWCNT‐NH₂, whereas the physisorption process was dominant for CO₂ adsorption on MWCNT.