Numerical Study of Face Pressure Effect on Surface Settlement in Soft Ground Mechanized Tunneling; Case Study Tehran Metro Line 7

Various underground spaces such as tunnels are constructed in urban areas for different purposes. These spaces are often located in soil media near to ground surface. In EPB tunneling, the face pressure (P) and backfill grouting pressure (G) are the most important factors to prevent the surface settlement. The 7th line of Tehran subway project is excavated by EPB machine. In this paper four section of 7th line tunnel are selected and the influence of face pressure on surface settlement are investigated numerically by PLAXIS Tunnel software. In two section of tunnel the results of numerical models are verified by monitoring instruments. In next two sections of tunnel, four status of face pressure: P=P0 (estimated initial pressure), P=1.5P0, P=2P0 and P=4P0 and for each state, five status of backfill grouting pressure: G=0, G=P, G=P+0.5 bar, G=P+1 bar and G=P+2 bar are considered and surface settlement are analyzed. Results show that an increase of %400 for face pressure lead to a decrease of maximum 5 mm in surface settlement. So in this project the influence of face pressure is trivial but the influence of backfill grouting pressure is more significant.