Numerical Analysis of Longitudinal and Lateral Ground Subsidence by Tunnel Excavation under the Intersection of Two Bridges

Abstract

Recently, the vertical section of the downtown area is very complicated. When drilling a tunnel such as a downtown area, the upper part of the tunnel has two or more structures. Therefore, in this paper, numerical analysis is performed using FLAC3D to see the ground subsidence caused by tunneling in such a complicated situation. The area reproduced in the numerical analysis is the area where “Seoul's internal circulation” in the Dongdaemun district intersects with the river bridge. A tunnel was drilled 100 m below the area to interpret the lateral and horizontal ground subsidence at the top. Numerical analysis proceeded in four cases. Case 1 has no structure at the top, Case 2 has a river bridge at the top, Case 3 has a speeding ring road bridge, and Case 4 has two types, a river bridge, and a speeding road bridge. Case 1 shows lateral ground subsidence shows the most similar ground subsidence shape to Peck's subsidence curve at all points, In Case 2, it shows an uncommon figure from several ground surfaces. A small area where the bridge is in contact with the ground, some uplifting and ground subsidence are prevented. Case 3 is similar to Case 1 in overall depression. In the case of a longitudinal settlement, the amount of settlement is almost the same as in Case 1. However, the maximum settlement amount increases by about 0.001 mm. Case 4 showed the largest amount of land subsidence. Looking at the longitudinal settlement curve, it can be seen that the settlement of ground gradually occurs as the excavation phase progresses, when the excavation makes the largest amount of ground settlement. Also, it can be seen that the sinking of the upper part is largely before the excavation surface has been excavated. It can be seen that in the case of a lateral settlement, where the subsidence is disturbed by the structure at the top of the tunnel. Subsidence due to the bridge piers does not change all subsidence. However, the maximum settlement amount will increase. Looking at the amount of settlement in the area not in direct contact with the bridge, the river bridge caused 0.039 mm, and the speeding way caused 0.001 mm settlement, and the amount of land settlement by the two bridges 0.04 mm. Even at 15 m, 90m, the river bridge, and the speeding road and two bridges are the same trends. Using the total, it is considered possible to calculate the maximum amount of land subsidence in the case where all the structures exist in combination. If the upper structure can be created with more cases the relationship can be predicted more clearly.