Static and Dynamic Stability Analysis of the Erkenek Twin Tunnels Damaged by the February 6, 2023, Earthquake in Türkiye

On February 6, 2023, two successive devastating earthquakes struck the Kahramanmaraş province in southern Türkiye. The first earthquake with a magnitude of Mw 7.8 occurred nearby Pazarcık, followed by a second Mw 7.6 quake in Ekinözü nine hours later. These events led to the tragic loss of over 50,000 lives and caused extensive damage to infrastructure, including transportation tunnels. The new Erkenek Twin Tunnels suffered significant damage due to ground shaking. These twin-tunnels were constructed in 2017 through jointed limestone and schist units, which each tunnel has a 7.4 m height and 10.30 m width, with a 40 cm reinforced concrete lining. The damage to the tunnels' inner linings was likely caused by mass movements triggered by intense shaking, the geological structure, and the low overburden near a valley. This study assesses the stability of the tunnels using pseudo-dynamic, pure dynamic limit equilibrium method (DLEM) analysis, and 3D dynamic finite element analyses using PLAXIS-3D. The research further investigates the causes of the damage and discusses their implications for seismic tunnel design. It is shown that the twin tunnels were vulnerable to be damaged by the motions induced by the twin earthquakes due to thin overburden, steeply dipping schistosity planes. This clearly indicated it is necessary to properly take into account the geological structure and possible earthquakes in the close vicinity of tunnels with low overburden and built next to steep-deep valleys.