Comparison of NATM and Traditional Tunneling Methods in Large-Section Tunnels (A Case Study : Tunnel-3 of the Main Pataveh-Dehdasht Road)

The traditional and NATM tunneling methods have been used in road, railway, and subway tunnels in the past three decades; yet, so far, there has been no academic and quantitative study on economic and technical comparison of these two methods for large-section tunnels, especially in soil. The present study is aimed to compare the NATM and traditional tunneling methods in large-section tunnels. For this purpose, the data of Tunnel-3 of Pataveh-Dehdasht road are used to design two traditional and NATM methods for this tunnel using Phase2 finite element software, followed by a technical and economic comparison of the two methods. Subsequently, the numerical modeling and design of the tunnel are performed using both NATM and traditional methods based on the existing geomechanical information. Once the results are obtained considering all design principles of both methods, the cost of designing the tunnel by each method is calculated. Accordingly, considering the conditions of the Tunnel-3 of Pataveh-Dehdasht road, using the NATM method will lead to a higher speed and safety of the execution and progression of the operation. Analysis of the obtained results indicated that the construction cost per meter of the tunnel length will be 10,007,930,898 IRR and 7,937,888,920 IRR (based on the list of construction unit costs for road, bands, and airports presented by the Management & Planning Organization in 2016) for the traditional and NATM methods, respectively. Therefore, the NATM method is more cost-effective than the traditional method by 26% in terms of tunnel construction cost