Selection of Optimal Single Tunnel Drilling Method in Soil (Case Study: Isfahan City Train Line 3)

Today, with the advancement of technology, the relative ease of drilling and underground construction, many countries have turned their attention to the construction of underground space. The need for an underground transportation system is evident in most major cities around the world, especially in areas with traffic congestion. This system requires a tunnel structure that is constructed in urban areas, mainly on loose lands and in shallow parts, and its impact can extend to the ground level. The choice of the best method for drilling these tunnels is a function of the soil characteristics, cross section and location of the tunnel, which should be considered according to the drilling area. In this paper, the mentioned cases have been investigated for Isfahan metro line 3 in the area of agricultural station which is to be drilled by NATM method in order to find the optimal drilling condition. The results show that the choice of drilling method pit can have significant effects on subsidence, tunnel cross-section deformation and horizontal displacement at the ground level. Based on the results, the effect of loading conditions, installation geometry, drilling pattern, different arrangement of surface structures, amount of overhead, dimensions of overhead application plate on tunnel behavior have been investigated.