AMIRKABIR
Year:2006 | Volume:17 | Issue:64-C|Papers Count:15

In this paper, formulation of a two-dimensional hybrid finite / boundary element method is developed for wave propagation analysis of linear elastic media in time domain. A modified set of well behaved full space two-dimensional elastodynamic convoluted kernels is presented and employed, that has a higher degree of accuracy than those presented by the previous researchers. Applicability and accuracy of the hybrid method are established by investigating seismic responses of half-plane, canyon and ridge sections as well as an underground explosion.

Transportation system can be considered as an interactive position of supply and demand. Designing the bus lines is considered as supply management, which is in fact making decision about promotion of bus transportation system within the circumstances of limited resources for investment and construction. Whereas Bus Transit Network Planning is a complex combinatorial issue, heuristic methods are used to solve this problem. Method of this research is Ant System algorithm. In each stage of this method which is inspired by normal behavior of the ants, it's tried to use factors of other searches in order to find the best answer. Using parameters involved in designing the bus network, concepts of this method are extended and adapted to Gazvin Bus Network Results show that using this method, can provide better routes based on the travel time reduction.

The measurement of soil parameters for unsaturated soil constitutive models needs extensive laboratory tests. For most practical problems, it has been found that approximate soil properties are adequate for analysis. Thus empirical procedures to evaluate unsaturated soil parameters would be valuable. The soil-water characteristic curve (SWCC) can be used to estimate various parameters, which describe unsaturated soil behavior. The SWCC is a relationship between soil suction and some measure of the water content. It can be measured or predicted based on the soil index properties. Estimation based on the index properties is highly desirable due to its simplicity and low cost.In this paper, a new model is presented for predicting the SWCC based on the soil index properties and Van Genuchten equation. Comparisons show that the SWCC predicted by this model is ill a good agreement with the experimental results.

Principal requirements for plastic concretes used in construction of cut off walls of dams, are a low enough elastic modulus compatible with the surrounding soil, adequate strength for loads sustained and adequate water tightness. Therefore means of reducing permeability without unduly increasing elastic modulus are important areas of research needed in this field.Considering the effectiveness of silica fume in reducing the permeability of normal and high performance concretes, in this research the extent of improvement in impermeability of plastic concrete through utilization of silica fume was investigated. The results obtained showed the substantial effect of incorporation of silica fume in reducing permeability and at the 15 percent replacement level of cement by silica fume, the coefficient of permeability was reduced 80 times. The utilization of silica fume also increased the strength and elastic modulus of plastic concretes. However the improvement in impermeability was more dominant and by increasing the water to cementitious materials ratio of plastic concrete containing silica fume it was possible to maintain the strength and elastic modulus at the level of control plastic concrete but achieve a 10 times reduction in permeability.

Nowadays, elecrochemical methods such as electrophoretic deposition are extensively used in industrial and laboratory activities, due to their high ability to control the surface morphology and the possibility for manufacturing different types of ceramic, metal and ceramic/metal composite bodies.In this research, ZrO2 electrolyte of solid oxide fuel cell is coatd on Titanium substrate. For this reason, first Zirconia powder was stablized in acetone and ethanol mixture by adding iodine and then electric field was applied between cathode and anode poles of cell that made the charged zirconia particles to deposit on the surface of Ti (cathode pole in cell). Effects of parameters such as solvent type, voltage, process time, zirconia powder and additive amounts in solvent plus sintering conditions in quality of coated layer were investigated.Results were shown that it could be possible to stabilize 20 (gI) of zirconia powder in two to one volumetric ratio of acetone and ethanol mixture by adding 1/2 (gI) iodine. Also applying 25 volt between the poles of cell for 20 minutes is suitable. Finally, the layer was sintered in 1250 °C temperature in hydrogen atmosphere for 2 hours.

The most important properties of Geostatistical Simulation are producing a group of images, which shows a range of possible events, calculating probable percentage of happening and also determining the risk in each step of process. 137 holes are drilled in this deposit. 3331 data from 125 drilled holes are gathered for grade estimation and reserve evaluation. Statistical studies show that Fe grade is not skewed and obey a natural model.plotting the empirical variogram in different directions show neither geometric nor regional anisotropy for the deposit. For simulating via SGS method, data are transferred to standard normal and then simulated 100 times (in this way 100 realizations were created). All of the realizations were honor to histogram and variogram of samples, so all realizations are valid. E_Type and probability maps are drawn in 12.5 meters intervals and grade-tonnage curves were drown for each realization. E_Type maps evaluate average 108 million tones with 56% Fe content for whole deposit. Grade-tonnage curves were showed the range of tonnage variance. That is between 97 and 116 million tones for whole deposit.

Ore loading and transport can constitute some 50% of the total operating costs in a typical opencast mine. Any small reduction in these components can therefore result in substantial savings in the total cost. In this paper, a mathematical model is introduced that aims to optimize equipment allocation in opencast mines. In this model, optimization of loading and transport machinery is carried out using goal programming with Fuzzy constraints. Since in a typical mine the output of any loader can be variable, Fuzzy values have hence been used for all variables. The devised model has been tested in Sarcheshmeh and Songun copper mines of Iran. Both mines are amongst the largest operations in the world. The flexible allocation system, prescribed by the model, resulted in 15% increase in the mine output, as opposed to the rigid method of equipment allocation.

The presence of numerous discontinuity planes in rock mass structure would decrease strength, increase deformability of the rock mass and make the mechanical behavior of the rock mass much more complex. The effect of strength, deformation and conductivity characteristics of discontinuities on physical properties of rock mass is even more important than characteristics of the intact rock itself. Because information is lacking, the transition from peak to residual values now often assumes to decrease either linearly or exponentially when the joints exhibit strain-softening behavior. Three types of artificial joints with angle i= 15, i=30 i=40 degree asperity under repeated direct shearing are performed in this experimental research. The progressive failure mechanism and strength degradation of rock joints after peak strength are monitored during shearing. The progressive degrading of shear strength parameter or index is examined according to two strength criteria (Barton and Patton). The JRC (joint roughness coefficient) value for a given profile is estimated by fractal dimension.

Development of underground tunnel networks sometimes necessitates tunneling in difficult ground conditions. Maintenance of tunnel face stability is one of the most important safety challenges in such tunnels. In this study, face stability of Pardis tunnels, which are excavated in an un-compacted conglomerate east of Tehran, is assessed. For this goal, three dimensional numerical models are used using FLAC3D software, showing that the type of tunnel wall support has no major effect on tunnel face stability. Moreover increase of tunnel face displacement with increase of overburden and progress of excavation of stages is quantified. The effect of installed bolts on the tunnel face to improve stability is investigated. The results show that installation of bolts in the tunnel face increases pressure on tunnel walls but have no effect on displacements around it.

In order to improve the analysis of cohesive slopes and vertical cuts, tensile crack modeling is used. Nonlinear elasto-plastic finite element analysis along with Mohr-Coloumb yield surface and associated flow rule has been utilized. Both formulations and numerical examples are presented in this paper. The results of test problems reveal that tensile cracks will reduce the factor of safety. This reduction is more pronounced when the soil slope gets steeper.

Pillar design and stability analysis is an issue that is faced routinely in mining and civil industries. In mining operations, while the establishment of several mining levels is often necessary to ensure adequate production, it does result in formation of pillars that must be recovered under high stress conditions at later stages of excavation. Moreover, in civil infrastructures, such as underground power stations, waste repositories, warehouses, etc., design of remnant rock pillars is necessary and very common. Therefore, it is beneficial to develop guidelines that help in the design of rock pillars as well as to maintain their long-term stability. The aim of this paper was to delve into the mechanism involved in rock pillar loading process and failure mechanisms. The effects of pillar geometry, pillar and surrounding ground stiffness were investigated on pillar failure mechanism. A thorough numerical analysis was carried out to investigate the pillar deformation and failure process under natural loading conditions. Accordingly, the obtained results were compared against field data, from Canadian mining operations, published by various researchers. A fairly good match was obtained between the numerical findings and published field data.

Correspondence Analysis Method (CAM) is a non-structural method that it could be used to find the anomaly, and to separate it from the background values. To apply this method, the representative samples of a large area are enough but the exact location of the samples is not important. Based on this method, the litho-geochemical data would be mathematically processed to extract the valuable factors needed for plotting a two by two diagram. This method has been applied on available data in Enjerd skarn deposit. The final factors are potentially able to separate the anomaly from the background by the amount of variable sample separations. Five factors (as the suitable representative factors) have been calculated by applying this method, which has resulted in a final matrix, with 5 columns. According to these factors, we could plot variety diagrams, resulting in the very accurate anomaly separations. In most cases, Co and Ni are paragenetically related, since they show very clear co-separation features.