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Abstract
One of the most important phases in tunnel excavation in urban areas is to design and make a place for assembling and establishing excavation machines into the earth. Since providing stable trench walls in loose earth environment is very important, this paper tries to use a nailing method to make trench walls stable in the entrance of the 2nd subway line in Tabriz. To do so, the effect of each of the nailing designing parameters in improving and stabilizing of entrance trench walls of earth pressure balance digging machines (EPB) of the 2nd line in the Tabriz subway were analyzed by limit equilibrium and numerical methods using two pieces of software, Plaxis 3D and Slide 5.0. Of all the parameters, nail length, nail axis incline angle with horizon level, distance from centre to centre of nails, and nail capacity are the most important ones affecting the amplitude reliance coefficient so that in this paper the researcher attempts to determine and provide the optimum condition of all mentioned parameters to get a desirable safety factor (1.4). Also, to confirm and compare the relationship resulting from these parameters, limit equilibrium method was used for different lengths of nails through numerical method by Plaxis 3D software. The paper tries to compare the relationship between the displacement amount and the strain percent established in amplitude due to excavation for each of the conditions in nail installing.