ABSTRACT
On February 6th, 2023, earthquakes with magnitudes of 7.7 and 7.6 struck Kahramanmaraş and eleven surrounding provinces, causing significant damage to buildings and infrastructure. Despite this, tunnels generally performed well during the seismic activity, showing only local cracks, concrete spalling, and minor portal damage, with no complete collapses reported. This paper focuses on the final lining of the Erkenek Tunnel, a 1,816-meter-long double-tube highway tunnel in Malatya. In Türkiye, rock tunnels in mountainous regions with high overburden are typically built following Austrian standards, using the New Austrian Tunnelling Method (NATM). Sprayed concrete is considered a permanent structure, with no load transfer to the final lining. The design of the unreinforced final lining primarily considers the self-weight of the structure and the loads from electromechanical equipment. Before the earthquake, final linings were usually constructed without reinforcement, except for localized areas as needed. This paper examines the response of both unreinforced and reinforced sections of the final lining during the earthquake. In contrast to road tunnels, NATM metro tunnels in urban areas, such as crossovers, platform tunnels, and cross-passage tunnels, are fully reinforced. The design of metro tunnels, typically in urban areas with shallow and varied soil and rock conditions, treats the initial lining as temporary and factors in final loads from groundwater, traffic, buildings, and seismic forces. Following the observed structural behavior of unreinforced tunnels during earthquakes, the final linings of road tunnels are now constructed with at least minimal reinforcement, in line with the 2018 Turkish Earthquake Code.
