Hazards of mechanized tunnel excavation in H<Subscript>2</Subscript>S bearing ground in Aspar tunnel,Iran

Occurrence of hydrogen sulfide gas (H₂S) is one of the most important engineering geological hazards during tunneling. Its hazards and consequent challenges are very difficult and costly to solve. During site investigation, one of the tasks for engineering geologists is prediction and evaluation of the risk of H₂S gas in the underground spaces. In this study, water conveyance tunnel of Aspar, which was excavated in H₂S-bearing environments, is discussed. The tunnel is excavated in the hydrocarbon formations. Applied experiments suggest that geological formations pertaining to hydrocarbon resources are crucial in formation and reservation of H₂S gas. This paper briefly discusses hazards and geological sources of H₂S, as well as remedial measures for decreasing the risks and problems in excavation of the tunnel. To predict the risk of H₂S gas in the underground spaces, it is possible to use some precursors such as: sulfur springs, organic traces, organic argillaceous rocks, exposure of H₂S odor from fresh surface of rock and smell of H₂S during boreholes drilling. Controlling the inflow of groundwater into the excavation, diluting the concentration of H₂S, training the personnel and utilization of some proper safety equipment have been used to mitigate risks and problems in tunnel excavation.     

Coupling of solid deformation and pore pressure for undrained deformation—a discrete element method approach

This paper presents a numerical scheme for fluid‐particle coupling that uses the discrete element method by taking into consideration solid deformation and pore pressure generation. A new water particle element is introduced to calculate pore water pressure due to porosity changes. The water particle element has the same size and shape as the solid element and experiences the same amount of deformation. On the basis of the effective stress principle at the element contact, the total force is equal to the sum of the force transmitted through the solid element contact and the water particle force due to pore water pressure. Analytical solutions of traditional soil mechanics problems, such as isotropic compression and consolidated triaxial undrained test, are used to quantitatively validate the proposed model. The numerical results show good agreement between the model and the analytical solutions. The model therefore provides an effective method to calculate pore pressure in a porous medium in discrete modeling.     

Estimating design probable maximum precipitation using multifractal methods and comparison with statistical and synoptically methods case study: Basin of Bakhtiari Dam

The probable maximum precipitation which is defined as the maximum precipitation at a particular location for a given duration is used as a design criterion for major dams. The assumptions of deterministic consideration and an upper limit to probable maximum precipitation have been repeatedly criticized by hydrologists. Nowadays, multifractal method which strongly contains physical bases can be used to improve the probable maximum precipitation. In this research, the universal multifractal model was used to estimate the design probable maximum precipitation for specified exceedence probability in basin of Bakhtiari Dam, southwest Iran, and its results were compared with statistical and synoptically methods. The results revealed that the return period of statistical and synoptically probable maximum precipitation, estimated for the different durations, are about 10⁹ and 10³–10⁴ years, respectively; also, over periods ranging from 1 to 7 days, the ratios of design probable maximum precipitations, estimated based on multifractal method for return period of 10³–10⁹ years, to statistical and synoptically probable maximum precipitation estimates ranged from 0.61 to 1.1 and 1.33 to 2.37, respectively. These results indicated that the multifractal method can be used to reasonably estimate the probable maximum precipitation.     

Time trend analysis of some agroclimatic variables during the last half century over Iran

Theoretical and Applied Climatology - We assessed the trends of precipitation, maximum and minimum temperature (Tmax and Tmin), diurnal temperature range (DTR), water requirement of autumn-planted...     

On the effects of higher convection modes on the thermal evolution of small planetary bodies

The effects of higher modes of convection on the thermal evolution of a small planetary body is investigated. Three sets of models are designed to specify an initially cold and differentiated, an initially hot and differentiated, and an initially cold and undifferentiated Moon-type body. The strong temperature dependence of viscosity enhances the thickening of lithosphere so that a lithosphere of about 400 km thickness is developed within the first billion years of the evolution of a Moon-type body. The thermally isolating effect of such a lithosphere hampers the heat flux out of the body and increases the temperature of the interior, causing the solid-state convection to occur with high velocity so that even the lower modes of convection can maintain an adiabatic temperature gradient there. It is demonstrated that the effect of solid-state convection on the thermal evolution of the models may be adequately determined by a combination of convection modes up to the third or the fourth order harmonic. The inclusion of higher modes does not affect the results significantly.     

On the moments of inertia differences of the moon

In this paper it is shown that the differences of the moments of inertia of the Moon are, most likely, due to the surface irregularities, the over-all front side mare fillings and the backside topography.     

Low-magnetic crust underlying South Province of Mars

The lack of distinct magnetic signatures observed by Mars Global Surveyor (MGS) over the impact craters and impact-related Quasi-Circular-Depressions (QCDs) with diameters greater than 200 km located on South Province, south of 30S and from almost the west of Hellas to Argyre basins, implies a weakly magnetized crust. Using MOLA topography and the recent JPL gravity model of Mars we determine the structure of the crust beneath the craters and impact-related QCDs, and show that the impacts that have created these features were capable of strongly disturbing the crust directly beneath. On the basis of theoretical magnetic anomaly modeling and shock demagnetization models, we demonstrate that the impacts are capable of demagnetizing the entire crust beneath and creating distinct magnetic anomalies at the satellite altitude of 400 km in case the crust was appreciably magnetized prior to the impacts. We derive the magnetic anomalies of these features using the radial component of the high-altitude nighttime MGS data. An upper limit of <2 × 10⁴ A for the bulk magnetization of the crust beneath South Province is estimated, which is about 30 times less than that underlying Terra Cimmeria and Terra Sirenum. Similar weak bulk magnetization is obtained for part of the crust surrounding Hellas, Isidis, and Argyre basins.     

Polar wander of Mars: Evidence from giant impact basins

We investigate the polar wander of Mars in the last ∼4.2 Ga. We identify two sets of basins from the 20 giant impact basins reported by Frey [Frey, H., 2008. Geophys. Res. Lett. 35, L13203] which trace great circles on Mars, and propose that the great circles were the prevailing equators of Mars at the impact times. Monte Carlo tests are conducted to demonstrate that the two sets of basins are most likely not created by random impacts. Also, fitting 63,771 planes to randomly selected sets of 5, 6, or 7 basins indicated that the identified two sets are unique. We propose three different positions for the rotation pole of Mars, besides the present one. Accordingly, Tharsis bulge was initially formed at ∼50 N and moved toward the equator while rotating counterclockwise due to the influence of the two newly forming volcanic constructs, Alba Patera and Elysium Rise. The formation of the giant impact basins, subsequent mass concentrations (mascons) in Argyre, Isidis, and Utopia basins, and surface masses of volcanic mountains such as Ascraeus, Pavonis, Arsia and Olympus, caused further polar wander which rotated Tharsis bulge clockwise to arrive at its present location. The extensive polar motion of Mars during 4.2-3.9 Ga implies a weak lithosphere on a global scale, deduced from a total of 72,000 polar wander models driven by Tharsis bulge, Alba Patera and Elysium Rise as the major mass perturbations. Different compensation states, 0-100%, are examined for each of the surface loads, and nine different thicknesses are considered for an elastic lithosphere. The lithosphere must have been very weak, with an elastic thickness of less than 5 km, if the polar wander was driven by these mass perturbations.     

Removal of heavy metals from paint industry’s wastewater using Leca as an available adsorbent

The ability of light expanded clay aggregate to remove lead and cadmium from paint industry’s effluents was studied at different levels of adsorbent, contact time and pH in April 2008. For this purpose, lead and cadmium removal from paint industry effluents were studied in batch reactors. lead and cadmium measurements have been taken with non-flame atomic absorption techniques and test methods were adapted from 19^th. Ed. of standard methods for the examination of water and wastewater. In this study, different amounts of Leca (1, 2, 3, 4, 5, 6, 7, 8, 9 and 10 g/L) were investigated. The amount of adsorbed lead and cadmium exposure to Leca increased from 1.41 to 3 mg/g and 0.22 to 0.75 mg/g, respectively. The maximum removal efficiency for Pb was 93.75 % at pH = 7 and exposure to 10 g/L of Leca, while for cadmium, it was nearly 89.7 % at the same condition. In this study, adsorption process of lead and cadmium was fitted with Freundlich adsorption isotherm (R² _Pb = 0.97 and R² _Cd = 0.98). The sufficient contact time was deemed 1–2 h for lead and cadmium. According to the results, Leca is recommended as a low cost and available adsorbent to remove lead and cadmium from industrial wastewater.     

Water quality variability and eutrophic state in wet and dry years in wetlands of the semiarid and arid regions

Wetland ecosystems are particularly vulnerable due to flow of nutrients from the surrounding watershed. The study was performed in the Shadegan wetland, a Ramsar-listed wetland located in the south-west of Iran at the head of the Persian Gulf. The wetland plays a significant hydrological and ecological role in the natural functioning of the northern Gulf. The proposed wetland has different water quality characteristics in wet and dry years of study during 1994–2006. To determine the variables, sampling was carried seasonally for each year at six stations. The results indicate that wetland in wet years had high concentrations of nitrate and silicate, leading to oligo–meso eutrophic conditions. Wetland in dry years had high phosphate concentrations, resulting in meso-eutrophic conditions. Forcing functions, such as climatic patterns, water residence time, reduce runoff and increasing density of wastewaters from the surrounding urban, agricultural and industrial area are probably the main variables that explain the observed patterns.