مجله زمین شناسی مهندسی
سال نهم شماره 2 (تابستان 1394)

This paper describes triaxial compression tests conducted to determine the effect of fiber inclusion on stiffness and deformation characteristics of sand-gravel mixtures. Tested soil was a mixture of Babolsar sand from the shores of the Caspian Sea and Karaj River gravel. Portland cement was used as the cementing agent and fibers 12mm in length and 0.023mm in diameter at 0%, 0.5% and 1.0% were added to the mixtures. Triaxial tests were performed on saturated samples in consolidated drained and undrained conditions at confining pressures of 100, 200 and 300 kPa. Deviatoric stress-axial strain, volumetric strain-axial strain, pore pressure-axial strain curves with deformation and stiffness characteristics were investigated. Tests results show that fiber addition increased peak and residual shear strength of the soil. Fiber addition resulted in an increase of the maximum positive and negative volumetric strains. In undrained condition, fiber inclusion caused increase in initial positive pore pressure and final suction. It has also been observed that fibers decreased initial tangent stiffness of the cemented sand-gravel mixture.

The studied region in this research (Alborz province) is structurally located in Alborz poly_orogenic system of northern Iran [1]. The purpose of this research is combining the remote sensing and geology sciences to show fault lineaments by analyzing satellite data in a vast region and also comparison between lineaments layer and recognized faults in geology maps. Firstly, two scenes of Landsat ETM+ satellite images with 164-35 and 165-35 numbers were mosaicked and also according to coordinates of research area (46 degree and 30 minute to 48 degree east longitude and 34 to 35 north latitude degree) have been crop. Then with remote sensing methods such as combination of bands, filtering, NDVI index to reconstruction the vegetation, principal components analysis (PCA) and band relativity in gray scale and color images have been analyzed the satellite images. Finally, by using the above mentioned methods, the map of fault lineaments and map of lineaments density for Alborz province have been prepared and compared with recognized faults.

In order to assess mineralogical composition influence on durability and strength of rocks, 4 samples of hornfelsic rocks were selected from southern and western parts of the city of Hamedan, west of Iran. These rock samples were subjected to mineralogical, physical and mechanical tests in the laboratory. Also, they were evaluated in 15 cycles of slake-durability testing in different pH of sulfuric acid solutions and XRD analysis. Based on the results, the type and amount of minerals, their density and hardness had an influence on the uniaxial compressive strength and the slake durability index of tested rocks. The results of slake-durability test indicated that weight loss of the samples at initial cycles was found to be higher than the end cycles. Also, in these samples, initial minerals in the fresh samples were not exchanged by secondary minerals such as clay minerals. Therefore Hamedan hornfelsic rocks are approximately resistant when put under accelerated chemical weathering and degradation in the laboratory and natural chemical weathering.

Recently, rock mechanics contribution in petroleum industry has significantly increased. Examples of these applications are wellbore stability analysis in horizontal wells, and sand production problem while extracting hydrocarbon from sandstone reservoirs. However, determination of the magnitude and orientation of the in-situ stresses is an important parameter for implementation of such kind of studies. The matter is so important that recently global endeavor for sharing practice to determine such expensive data is formed, and world stress map is being developed based on information provided by individuals around the world.In this research attempts were made to estimate the in-situ stresses acting on a hydrocarbon reservoir based on routine activities of acid injection in oil reservoir. It was found that the relation between the re-opening pressure of fracture and principal in-situ stresses can be estimated using rock mechanics equations for the circular underground cavities. An appropriate relation between the maximum and minimum horizontal principal in-situ stresses and reservoir parameters such as permeability, reservoir pressure, Young’s modulus, acid viscosity, injection flow rate and etc, was developed by using the well-known Darcy equations for fluid flow in porous media. Accordingly, knowing the flow rate of acid injection during well stimulation operations and some other reservoir parameters, in-situ stresses may be estimated. This approach is innovatively creating further significant knowledge regarding the reservoir mechanics, using the routinely available acid fracturing data. The method was then successfully applied to a giant carbonate reservoir in SW of Iran. Maximum and minimum effective horizontal stresses were calculated by employing the presented method. The significance of this approach may be distinguished at the local and global scale by helping for better correlation and development of in-situ stress data at oil-rich states around the world.

This paper aims to present an experimental and numerical study on the effect of wetting-drying cycles and plasticity index on the California Bearing Ratio of lime stabilized clayey soils. The numerical analysis is carried out based on finite element method for comparison between results of experimental and numerical studies. Three clays with different plasticity index mixed with various amounts of hydrated lime and compacted at optimum water content. The CBR tests conducted to the reference soils and admixtures after specified curing time and various numbers of wetting-drying cycles. The experimental results indicate that, addition of lime content up to 4% caused significant increase in the CBR values. The results also reveals that, the CBR decreases during the wetting phase and increases during the drying phase of each cycle, and after 3 cycles the CBR values of lime stabilized clayey soils is increased. Comparison between numerical and experimental analysis indicate correspondence of results.

In all three types of metallic pollution indices (accumulative or comparative, enrichment and ecological risk indices) the bulk concentration of metals in the sediment sample is considered. Such point of view indicates that all chemical forms of a given metal have an equal impact on the environment which may not be regarded reasonable. In order to include the effect of metal fractionation in sediments for estimating the pollution risk to the biota, developing a risky pollution index (IR) has been considered in this study. In contrast with Mobility Factor (MF) and Risk Assessment Code (RAC) indices, IR attributes a risk share to metal species bound to reducible and oxidizable phases which are totally neglected in both two above-mentioned indices. In other words, besides the absolutely mobile fractions, the potentially mobile ones are also regarded in risk evaluation process elaborated by IR. The different structure of the newly-developed index may prevent risk level underestimation especially in case where a remarkable percent of bulk concentration is accumulated within reducible and oxidizable phases. The independency of the index value to the bulk concentration makes it possible to discuss the potential risk in different levels of bulk concentration. Furthermore, the index capability in indication of risky pollution regardless of the pollution source type may prevent the probable misleading caused by distinct separation of bulk concentration into geopogenic and anthropogenic portion.

Collapsible soils which are mainly found in hot and dry regions are generally showing a considerable amount of decrease in their volume by increasing the humidity. This kind of soils could wildly be found in central part of Iran and has caused lots of problems for roads and railroads in that region. One of these railroads is Tehran-Semnan railroad which connect the capital city, Tehran, to central part of Iran. Appearance of wide cracks in the collapsible soil near the rail tracks has caused some worries about the safety and performance of the railroad. However, due to the high traffic of the railroad, it is impossible to block the road for remedy. Therefore using injection method has been found the most suitable alternative to improve the soil along railroad. In this paper, different characteristics of injection of different materials such as lime, cement and micro-silica have been studied. A comparison has also been done between behaviors of soils that have been remedied by injection of these materials. The results of field and laboratory tests revealed that the injection of lime has better effects on improving soil characteristics than the other materials. It will significantly decrease the collapsibility potential of soil in saturate condition and will cause an increase in loading capacity of soil. Lime injection has been suggested as the most appropriate solution for projects with similar geological condition.