Modeling, stress distribution and the change of ground behavior during excavation of Tehran city underground tunnel

From these factors the tunnel form, dimensions, depth, the tunnel drilling method, presence of water, etc. can be mentioned. Achieving an optimized design requires identification of effective parameters and the relationships among them. Effective design parameters include stability of the tunnel face, horizontal and vertical displacement, seismic wave, and shrinkage phenomenon, etc. Also considering the importance of the structural stability on the ground surface above the tunnel, especially in the urban tunnels, the settlement level of the ground surface must be considered. In this study the stability of an 8m width and height horseshoe sectioned tunnel located in Tehran alluvium having been projected for water transmission has been technically analyzed using the FLAC 2D‎‏ software and the comparison wad made using empirical and analytical methods. The results showed that the maximum settlement resulting from design step using software is 14.9 mm which is almost consistent with the value obtained from the empirical relationship, and the difference estimation lies within the acceptable range (0.7%). Also the obtained horizontal displacement shows that the maximum displacement within the 25m distance from the tunnel axis (on both sides) is 2mm and the values obtained from the empirical relationship showed that the maximum horizontal displacement occurs on the 25m distance from the tunnel axis.