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- 저자 : Fahimifar (검색결과 4 건)
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The ground response curve of underwater tunnels, excavated in a strain-softening rock mass
Fahimifar, Ahmad,Ghadami, Hamed,Ahmadvand, Masoud Techno-Press 2015 Geomechanics & engineering Vol.8 No.3
This paper presents an elasto-plastic model for determination of the ground response curve of a circular underwater tunnel excavated in elastic-strain softening rock mass compatible with a nonlinear Hoek-Brown yield criterion. The finite difference method (FDM) was used to propose a new solution to calculate pore water pressure, stress, and strain distributions on periphery of circular tunnels in axisymmetric and plain strain conditions. In the proposed solution, a modified non-radial flow pattern, for the hydraulic analysis, is utilized. To evaluate the effect of gravitational loads and variations of pore water pressure, the equations concerning different directions around the tunnel (crown, wall, and floor) are derived. Regarding the strain-softening behavior of the rock mass, the stepwise method is executed for the plastic zone in which parameters of strength, dilatancy, stresses, strains, and deformation are different from their elasto-plastic boundary values as compared to the tunnel boundary values. Besides, the analytical equations are developed for the elastic zone. The accuracy and application of the proposed method is demonstrated by a number of examples. The results present the effects of seepage body forces, gravitational loads and dilatancy angle on ground response curve appropriately.
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Semi-analytical solution for time-dependent deformations in swelling rocks around circular tunnels
Davoud Parsapour,Ahmad Fahimifar 한국지질과학협의회 2016 Geosciences Journal Vol.20 No.4
Underground structures in swelling rocks bear timedependent swelling effects. Upon excavation of underground spaces, the state of stresses and displacements change compared with the initial state. The stress and displacement variations depend on tunnel advance and the rheological behavior of surrounding rock mass. The swelling behaviour of rocks is known as a complicated phenomenon and very important task in tunnel design process. The paper aim is to predict the time-dependent displacement of the tunnel after the excavation has stopped or after installing the support system. The assumption is made that the medium around tunnel is both isotropic and homogenous. The section of tunnel is also assumed circular which in view of stress field, is excavated in Hydrostatic and non-hydrostatic conditions. A semi-analytical model on the basis of experimental results is adopted to evaluate the ground swelling strains as a function of time and stress. Given the current assumptions and conditions, a semi-analytical solution is derived to predict the time-dependent displacements and lining pressure for a circular shaped tunnel section in a swelling ground. Eventually, the model is loaded by an axisymmetric far-field pressure and the effect of the tunnel face on the lining pressure is also considered. On the whole, the comparison between modeling results and actual data, proved an accordance between them. As the results indicate, such parameters as, time dependent modulus of swelling and swelling strain coefficient as well as the initial aspect ratio, play a prominent role in controlling the swelling deformations. The set up time of lining is also considered as an impressing factor controlling the swelling pressure. In mediums of high swelling potential, the temporary support system installation has to be made to allow some ground deformations prior to the permanent support (lining) gets installed which causes the swelling deformation to get relieved.
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Mohammad Reza Zareifard,Ahmad Fahimifar 대한토목학회 2016 KSCE JOURNAL OF CIVIL ENGINEERING Vol.20 No.7
In this paper, an analytical method, for calculating seepage induced stresses and displacements in underwater lined circular pressure tunnels, is developed on the basis of a generalized effective stress law. The problem is considered as axisymmetric, and the lining and rock mass are assumed to be elastic, homogeneous and isotropic. The solution accounts for the seepage forces with the steady-state flow and hydro-mechanical pressures between adjacent zones. The proposed method can be applied for the analysis and design of pressure tunnels with concrete lining, prestressed concrete lining, grouted rock mass, as well as for the analysis of pressure tunnels considering the effects of the surrounding fractured or damaged zone. Illustrative examples are given to demonstrate the performance of the proposed method, and also to examine the effect of seepage forces on stability of pressure tunnels. It is concluded that, the classic solutions (Lame’s solution), that is based on considering the internal pressure as a mechanical load applied to the tunnel surface, is not applicable to pervious media and results in unsafe designs.
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Waseem Daoud,Taghi Ebadi,Ahmad Fahimifar 한국화학공학회 2015 Korean Journal of Chemical Engineering Vol.32 No.6
Response surface methodology (RSM) was applied to evaluate the effect of the main operational variables, including initial pH, initial chromium ion concentration, bulk density of GAC and time on the removal of hexavalent chromium Cr(VI) from contaminated groundwater by permeable reactive barriers (PRB) with acid-modified granular activated carbon (GAC) as an adsorbent material. The removal rates of Cr(VI) under different values of these parameters were investigated and results indicated high adsorption capacity at low pH and low initial metal ion concentration of Cr(VI), but the bulk density of GAC slightly influenced the process efficiency. According to the ANOVA (analysis of variance) results, the model presents high R2 values of 94.35% for Cr(VI) removal efficiency, which indicates that the accuracy of the polynomial models was good. Also, quadratic regression models with estimated coefficients were developed to describe the pollutant removals.
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