AMIRKABIR
Year:2003 | Volume:14 | Issue:55-E|Papers Count:8

A stress path triaxial testing study entailing compression extension and compression tests at constant major principal stress was performed on coarse Cambria Sand prepared with cross; anisotropic fabric in cylindrical specimens. Height-to-diameter ratios of 1.44 1.86 2.22 and 2.68 as well as different end conditions were employed to study the sand behavior in the range of applied effective confining pressures from 200 kPa to 4000 kPa. The compression test results were well comparable with those in the previous investigations as follow. 1) The tendency for dilation decreases with increasing confining pressure. 2) The friction angle decreases with increasing confining pressure. 3) The strain-to-failure increases with increasing confining pressure. 4) The strength increases with decreasing height-to-diameter ratio for specimens without lubricated ends. 5) The maximum rate of dilation occurs at the failure point. 6) Specimens with restrained ends exhibited higher strengths than specimens with free or lubricated ends. However the mode of failure appears to have been influenced seriously by the boundary conditions which in turn changes the stress-strain and volume change characteristics. In extension tests all specimens failed by development of shear planes either in the mid-section of the specimens in tests at low confining pressures (less than 1000 kPa) or under the cap in tests at higher confining pressures (more than 1000 kPa). Comparison of results from the extension tests shows that. 1) The strain-lo-failure in extension tests is smaller than that in compression tests. 2) The stress-strain curves after failure in extension tests become steeper as the confining pressures increase and their rates of stress decrease are much higher than those in compression tests. 3) The strain-to-failure increases as the confining pressure rises up to 1000 kPa and thereafter it decreases irregularly. 4) More meaningful and reasonable results are obtained from compression tests in which shear planes develop after peak failure than from extension tests in which shear planes develop before peak failure.

Flow aeration downstream of normal gates in bottom outlet conduits has been found to be an effective and cheap way to eliminate cavitations damages. Studies on aerators have been focused on the question of how much air is entrained into the flow for different geometry of aerators and flow conditions. Designers of the aerators use empirical equations to calculate the quantity of air required by the aerators. The area of the aerator is determined using empirical relationships assuming the air velocity not exceeded a certain values. This paper is based on the results of hydraulic model studies of new bottom outlets recently constructed and examined at Water Research Center of Iran. The results consist of Jareh Karkheh Kosar Dasht-e-Abbas and Eilam bottom outlet dams in Iran. The model studies showed two different mechanism of flow aeration. These mechanisms depend on the geometry of conduits downstream of the gates with respect to the upstream geometry. It is hopped that this information provides a better understanding of the process of aeration for the designers of such structures.

The non-linear buckling of arches and cylindrical concrete shells are investigated in both elastic , and inelastic material properties in current study. For this purpose, the mathematical solution of system with one degree and two degrees of freedom are presented. The arches and shells are divided into two groups, deep and shallow and the geometrical nonlinearity in stability analysis is one of the major theme of the presented work for higher order degrees of freedom, the numerical models are made in ANSYS environment. The analysis was performed in 2-D and 3-D with beam, shell and solid elements for concrete. The steel reinforcement is also taken as separate element and is modeled as link element. Both geometrical and material non-linearity due to stability analysis, cracks and crushing of concrete are included in analysis. The extent parametric study shows the importance of some geometrical terms on load carrying capacity of arches structures: Also, the stress relaxation of concrete cracking on buckling load is measured

Discrete Element Method (DEM) can be used for numerical analysis of different geotechnical problems such as slope stability bearing capacity of shallow foundation and relative displacement of rock masses. In this research an effort is made to use the method for determining bearing capacity of foundation. To do this a computer program called BCAP (Bearing Capacity Analysis Program) is developed In this model the foundation can rest on a horizontal or inclined slope surface. The bearing capacity of strip shallow foundation is analyzed by "DEM" in both static and pseudo-static conditions. The soil mass is modeled as several discrete blocks connected with Winkler springs. Similar to the conventional bearing capacity theories tire failure of footing occurs by a wedge of soil below the footing pushing its way downward into the soil. The geometry of the failure surface is not f red and can be altered due to the all factors affect the problem. The geometry of the failure surface under the foundation is determined by four independent angles. By the trial and error the optimum. Shape of failure surface beneath the foundation can be found this optimum failure surface is corresponds to the minimum-collapsing load. Dynamic seismic forces are replaced by horizontal acceleration factors in a semi-static manner affecting on foundation. The paper includes several examples to explain the capability of the method. Also the results are compared with the other methods currently used for ultimate bearing capacity of shallow foundations. Several graphs are presented expressing the bearing capacity's coefficients for foundation on horizontal and inclined surfaces in the conditions of static and pseudo-static forces for various internal friction of underneath soil.

Ultimate shear strength in earthquake resistant masonry walls has especial importance. Horizontal loading in masonry walls (parallel to the Joints) causes horizontal shear failure between mortar and brick or diagonal tension failure. In masonry shear connection naturally is independent of mortar strength but perforated bricks because of mechanical shear keys with mortar cause increase in shear strength (at least in case of low vertical pressure on masonry). Masonry strength against horizontal shear failure would increase directly with vertical loading on brick and mortar. So in the case of high vertical pressure failure is due to diagonal tension and above the key effects they are not very significant.

At present about 90% of Mashhad water consumption is supplied by deep wells. This high level of consumption indicates the importance for monitoring groundwater quality in this area. There is a need for a dense network to be able to extend the point data to unpaged locations. The adequacy; of Mashhad water supply deep well network for monitoring nitrate and electrical conductivity (EC) has been investigated in this research by kriging which is an optimal interpolation technique based on spatial structure of data. An exponential model of semivariogram was fitted to nitrate data (after removing its trend by a second order equation) while EC data showed a linear-sill one. On the whole nitrate was more variable than EC with higher error of estimate. However the error maps showed that the variation of error was not so great in the study area for both parameters. Three new well locations were proposed for decreasing the maximum error of estimates. These locations were around the boundaries of the study and reduced the maximum error by less than 3%. Such a reduction is quite insignificant; illustrating that based on the available data the performance of the present network cannot be improved. Despite this the need for an optimum: network with a better spatial and temporal distribution is felt

To evaluate the hydraulic parameters of hard in Iran usually methods like Jacob method are commonly used. But as we know, such methods are not able to evaluate hydraulic parameters of hard aquifers accurately. In this study, using double porosity model of Warren & Root and graphical method of Kruseman & Ridder, three pumping test in hard aquifers (two in Shotori dolomite in Tabas region and one in Asmari limestone near Shiraz) have been interpreted and transmissibility of aquifers, storage coefficient of matrix and fractures, as well as the coefficient of flow exchange between porosities (A) and ratio of fracture capacity and capacity of whole reservoir (ω), have been calculated. Finally, double porosity model has been developed for partially penetrating wells and a computer code has been written in Matlab (5.3) to do all the calculations due to Kruseman & Ridder graphical method for interpreting pumping tests of hard aquifer wells for both fully and partially penetrating wells, automatically.

Diaphragm walls are frequently used in civil Engineerig projects. Considering the variety and important volume of consumed materials (concrete, anchors and soil),one of the important factors for design and construction of these walls, are their behavior under different executive ,and loading conditions. In this paper, various models of concrete diaphragms with different number of anchors and soil parameters under static and dynamic loading have been investigated using finite element method with nonlinear models. Results including the internal forces in diaphragm walls, variation of forces in the anchors, shape of the sliding surface and variation of pressure in soil are obtained and compared .An experimental tool with suitable measurment systems for determinig the pressure and internal forces was designed and realised. Also with similitude and dimansional analyses, diaphragms with different number of anchors were built and set on the shaking table test and experimented under different accelegrams. Finally results of nonlinear dynamic analysis were compared with experimental results.