Investigation of the Feasibility of Increasing the Tail-grouting Zone during Mechanized Tunneling in Sandy Soils

Nowadays, excavation in urban environments can have many risks; one of these hazards is improper tail-grouting of Earth Pressure Balance Machine (EPBM) and the consequent ground surface settlement. Failure to fill the tail space with suitable grout significantly affects the surface displacements. Injecting more grout to penetrate deeper around the tunnel will play a more effective role in reducing displacements and permeability of the soil. Therefore, experimentally investigation of the feasibility of increasing the tail-grouting zone during excavation around the tunnel space and the effect of this penetration on the amount of ground surface displacements is the main purpose of this paper. Thus, experimental tests were performed with different grout injection pressure and the effect of each of the pressure on the penetration depth of grout into the soil new laboratory model were examined. Then to study the effect of the grout penetration depth on surface settlement to determination of the adequate amount of grout injection pressure a numerical modeling of Tabriz metro line 2 by FLAC3D software were completed. For this purpose, the results of the laboratory tests (the penetration depth of grout) were used in numerical modeling. The results indicated that the amount of penetration in the implemented granulation has increased due to the increase in pressure, so doubling the pressure causes a 30% increase in grout penetration in the surrounding soil. The results of numerical studies showed that increasing the range of injection in the modeling causes a significant reduction (80 percent) in the ground surface settlement.