Abstarct: Construction of tunnel and underground spaces in urban areas are daily developing. Most of these spaces are excavated in soil bed due to adjacency to ground surface. One of the important and effective concerns in construction of underground spaces is cost and development rate of the project, therefore in this research by concentration on two sections of Mashhad urban subway line2 tunnel, excavation in open mode for cost and also excavation time reduction has been investigated. After analysis of these two sections by FLAC3D software, in the first section it was shown that in spite of appropriate geological conditions of this section, settlement value has exceeded the allowable value and reaches 4.4 centimeters in tunnel heading and 3.3 centimeters in tunnel face. Also in the second section settlement value in heading and face of tunnel was resulted 4.9 and 6.9 centimeters respectively. According to the results, it was determined that excavation risk in open mode in these sections is high due to the exceeding of settlement value from allowable limit and excavation probability in open mode is reduced and so it can't be excavated in this mode. After modeling by applying %50 and %100 of the calculated pressure to face in the first section, it was observed that the settlement value in face is reduced to 5.7 millimeter and 2.6 millimeter respectively. Also by applying %50 and %100 of the calculated pressure to face in the second section, it was observed that the settlement value in face reaches 9.6 millimeter and 1.5 millimeter respectively. According to the allowable limits of settlement by applying %50 of the calculated pressure in both sections, it is observed that the settlement values in this situation has been reduced rather than the case in open mode that it increases excavation probability by applying pressure of %50 and hereby injection foam volume is reduced as well as reduction of material volume filled in the pressure chamber and as a result, it followed by decrease in costs of the project.