Abstract
Stability of large underground structures depends on not only rock mass conditions but also excavation stages and support systems. In addition, complexity of geological conditions and interaction of excavation with in situ conditions affect the performance of design. The Akyazı tunnel (Trabzon, Turkey) is 2478 m long and was designed as 3 lanes and double tubes, and the number of lanes at the junction part increases to 5. Tunnel cross-sectional area from the Akyazı tunnel reaches 3 lanes and 150 m2 to 5 lanes and 438 m2 gradually. The width of the tunnel at the junction point reaches to 31 m. In this study, the necessity of inner lining concrete in tunnels excavated in good rock mass conditions is assessed and the results of the analyses are discussed. The inner lining concrete increases the cost of tunnel construction, as well as extending the construction period. With the procedure followed in the Akyazı tunnel, the top heading part of the tunnel was constructed without inner lining. No stability and drainage problem have not been encountered for 4 years. Currently, the tunnel construction was completed successfully, and the tunnel was opened to traffic. Consequently, the excavation stages, support systems described, and especially inner lining necessities discussed in this study may be applicable for extremely large tunnel sections.
Highlights
The effective transportation is one of the basic requirements of sustainable developments, and one of the important components of effective transportation system of urban areas is tunnel
The geological strength index (GSI) for the lithological unit along the expansion section was determined in accordance with the GSI system proposed by Hoek and Marinos [24] (Fig. 5), taking into account the data obtained from the outcrops and borehole of TSK-5
When the deformations calculated at point 4 were examined, 0.4 mm deformations occurred during the tunnel expansion excavation, and this value increased to 5.2 mm when the expansion phase was completed
Summary
The effective transportation is one of the basic requirements of sustainable developments, and one of the important components of effective transportation system of urban areas is tunnel. Neuner et al [18] stated that a single permanent shotcrete lining can fulfill the reduced requirements and offers a very economic tunnel design, in some cases, and they proposed a detailed finite element model for analyzing the bearing capacity of the permanent shotcrete lining on the basis of an advanced constitutive model considering the time-dependent and nonlinear material behavior of shotcrete. When considering these studies, it is evident that large-span tunnels and inner lining necessities are still not solved completely. Numerical analysis methods for large diameter tunnel with an excavation diameter of 31 m are applied, and the experiences obtained from the study are presented
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