INFLUENCE OF MIX GROUND AND SPACE AROUND NEW TUNNEL ON EXISTING TUNNEL SETTLEMENT DURING CROSSING SHIELD CONSTRUCTION

A majority of the metro constructions in coastal area especially Guangzhou region are built in multi-strata ground. For this propose,a simplified geological model is proposed.With 3D-FEM,the influence of under-crossing construction on the displacement of the existing tunnel under different types of multi-strata ground,the thickness of the overlay soil and the distance of two tunnels is studied.The results show that when the new tunnel building in the homogeneous ground,the displacement is the maximum.The displacement for the case of upper-soft and lower-hard ground takes the second place.The displacement for the case of hard stratum is the minimum.The displacement of the existing tunnel decreases as the soil parameters increase.The displacement of the existing tunnel increases as the thickness of overlay soil increases and decreases as the net distance of two tunnels increases.When the net distance is less than 2 times of lining diameter,the displacement of the existing tunnel is great and the existing tunnel has risk of damage.Finally,corresponding measures are suggested to control the settlement effectively.