Tunnel Face Stability Analysis in Soft Ground in Urban Tunneling by EPB Shield (Case Study : 7th Line in Tehran Metro)

Traffic congestion and environmental factors are creating a demand for greater utilization of underground spaces in urban areas. In mechanized excavation of subway tunnels, the Earth Pressure Balanced Shield (EPBS) has been developed in the recent decades for managing the instability of the excavation profile in complicated geotechnical conditions in urban areas. During the advancement of an EPBS, the face-stabilizing pressure is one of the most important factors of critical and principle to be evaluated correctly. In tunneling by EPBS, high face pressure often leads to surface upheaval whereas low face pressure leads to sudden collapse of the face and ultimately settlement of the surface. Both of these misevaluated pressures may cause the damages which followed by pert of time and finance. This paper is discussed about urban tunneling by EPBS in soft ground conditions and focused on calculation of face-stabilizing pressure applying to the case of 7th line in Tehran metro project. Face-support pressure is estimated by most current methods of limiting equilibrium analysis and limiting analysis in excavated parts (two stations) of direction with different and difficult geotechnical conditions. Obtained results compared to EPBS operational results which showed the results of Broere analytical method is most attractive and realistic among others. For one of the excavated stations calculated value of the Broere analytical method obtained 78.406 KPa and EPBS actual value was equal to 81.01 KPa. Due to results verification that illustrate a good adjustment with the actual values, quantity face-stabilizing pressure is predicted for some of the alignment unexcavated stations (S7, V7, W7 and X7) which can be used in built procedure. Maximum value was quantity 246.351 KPa for station V7 and minimum value obtained quantity 25.866 KPa for station W7.

کلیدواژه ها:

Tunneling ، face-stabilizing pressure ، EPBS ، analytical method ، 7th line of Tehran metro