جستجوی مقالات مرتبط با کلیدواژه "flac 2d" در نشریات گروه "عمران"

Seismic loads may damage municipal solid waste landfills (MSWLF) through the relative movements within the waste, bottom lining system, cover system, foundation, and interfaces. The smooth synthetic materials might be placed beneath the structures to provide seismic protection by absorbing the imparted energy of earthquakes through the sliding mechanism. In the present study, experimental investigations were conducted in order to evaluate role of in-soil base isolation on seismic response of the Kahrizak MSW landfill. Shaking table tests were conducted on the MSW embankment isolated by semi-elliptic shaped liners and subjected to harmonic sinusoidal base excitations. Furthermore, the shaking table model was simulated by numerical analysis. The results of the isolated and non-isolated cases are compared in terms of permanent displacement and seismic response. Subsequently, the behavior of the numerical model was evaluated for different parameters. A reasonable agreement was found between the results of the physical model and the numerical model in prototype scale. The efficiency of in-soil isolation increases with increasing the amplitude of input motion. The results show that increasing the shear modulus reduces the amount of spectral amplification and relative displacement. It was also observed that as the age of the MSW increases, base isolation increases the displacement and crack width. Moreover, employing flat liner facilitates the movement of the ridge to the sides; and the concave liner prevents the wedge to move and, hence the quantity of settlement is reduced.

Increasing urban populations and creating traffic problems, the use of the underground spaces in the transportation is inevitable. Recent studies have shown that seismic response of ground on tunnels can differ from free field movement during earthquake and change the model of propagation of seismic waves. However, these effects have not been used in the seismic standards for the design of surface structures. In this research, using the finite difference method and FLAC 2D software, the effects of tunneling on earthquake amplification on the surface has been studied. For this purpose, the variation of the shear wave velocity of the soil under harmonic waves by different frequencies and amplitudes in both forms of the presence of a tunnel and in the free field have been investigated. The results of the studies showed that soil hardness and frequency of waves have a significant effect on the site response, and can increase the acceleration of the surface in harmonic waves to about 1.3 and with the acceleration of the Bam earthquake to about 1.7 times. Whereas, the presence of tunnel does not affect at longer distances of 15 times its radius. The coefficients obtained the site response can be used in seismic zoning of urban areas and for the design of seismic structures in the area affected by the tunnel.

Liquefaction is one of the destructive phenomena that every year causes a lot of damages to engineering structures. Tunnels are a type of engineering structure and they are considered as one of the most important and essential requirements of modern urbanization. Depending on their rigidity, these structures are affected by various deformations based on their surrounding soil. In saturated sand soils by applying dynamic load in untrained condition, pore water pressure increases, effective stress between particles decreases and shear strength is removed and consequently it results in consistency of soil , and imposed internal forces on tunnel lining, deformations and surface settlements have increased compared to static state. In this study, by using FLAC-2D software the single and twin tunnel has been modeled and the effect of changes in soil parameters (friction angle, adhesion, elastic modulus and Poisson coefficient), geometric characteristics of the tunnel (diameter, embedded depth and distance of tunnels) and harmonic load characteristics (frequency, load range) on surface settlement and internal forces of tunnel lining have been investigated through static and dynamic analysis. This study showed that in soils that are susceptible to liquefaction, these parameters will have a significant effect on surface settlement and internal forces of the tunnel lining. One of the findings is the reduction of liquefaction potential, surface settlement and increase of internal forces by increasing the adhesion and embedded depth. In this study the results are presented in detail using charts and tables.

Soil liquefaction describes a phenomenon whereby a saturated or partially saturated soil substantially loses strength and stiffness in response to an applied stress, usually earthquake shaking or other sudden change in stress condition, causing it to behave like a liquid. If the pressure of the water in the pores is great enough to carry all the load, it will have the effect of holding the particles apart and of producing a condition that is practically equivalent to that of quicksand the initial movement of some part of the material might result in accumulating pressure, first on one point, and then on another, successively, as the early points of concentration were liquefied.The phenomenon is most often observed in saturated, loose (low density or uncompacted), sandy soils. This is because a loose sand has a tendency to compress when a load is applied; dense sands by contrast tend to expand in volume or 'dilate'. If the soil is saturated by water, a condition that often exists when the soil is below the ground water table or sea level, then water fills the gaps between soil grains ('pore spaces'). In response to the soil compressing, this water increases in pressure and attempts to flow out from the soil to zones of low pressure (usually upward towards the ground surface). However, if the loading is rapidly applied and large enough, or is repeated many times (e.g. earthquake shaking, storm wave loading) such that it does not flow out in time before the next cycle of load is applied, the water pressures may build to an extent where they exceed the contact stresses between the grains of soil that keep them in contact with each other. These contacts between grains are the means by which the weight from buildings and overlying soil layers are transferred from the ground surface to layers of soil or rock at greater depths. This loss of soil structure causes it to lose all of its strength (the ability to transfer shear stress) and it may be observed to flow like a liquid (hence 'liquefaction'). The effect of structure on liquefaction potential of soil is very important, because it may prevent the occurrence of liquefaction phenomena or may to increase the intensity of liquefaction in the lower layers; hence the surcharge due to structures can be an important factor in the occurrence of liquefaction. Therefore in this study to model the surcharge of constructing a structure on liquefiable soil, first introduced the finite difference numerical analysis, then using FLAC 2D nonlinear dynamic analysis modeling of surcharge is carried. In this analysis, the modeling of surcharge due to building on a liquefaction soil and the effect of liquefaction potential of the economy has been studied. Also, the validation process and ensure the results of numerical analysis, modeling and comparing the results with a numerical model of centrifuge tests have been conducted. Results showed a significant decrease in the use of numerical modeling cost structures will be studied.

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