Experimental investigation and failure analysis of the adobe Hittite city wall in the UNESCO archaeological site of Arslantepe (Turkey)

This study presents a seismic vulnerability assessment of the main Hittite adobe wall at the Arslantepe UNESCO site in Turkey. Following its recent excavation, the 3000-year-old adobe structure was digitally surveyed in 2023 via laser scanning, photogrammetry, and drone imagery. Tests carried out on specimens delivered a mean compressive strength of around 0.70 MPa and a mean friction coefficient of 0.60. The experimental mechanical properties were used in an incremental non-linear dynamic analysis addressed to understand the residual seismic capacity of the wall and the failure mechanisms in case of future earthquakes on the building site. The numerical analysis incorporated both the undamaged state, featuring horizontal nonlinear contact interfaces, and the damaged configuration, which included both horizontal and vertical interfaces. The collapse time was derived from the intersection between plastic dissipation energy time-history (TH) and strain-energy TH. Analysis results show that the sections more at risk are those in proximity of the centre of the wall. Moreover, an earthquake of intensity 1/5 that of the 2023 seismic main shock would cause irreversible damage to the wall, originating shear and sliding failure mechanisms. A retrofit based on the substitution of the external layers of the wall with adobe blocks mixed with sisal fibers is numerically assessed. A percentage of fibers by around 0.8% would increase the seismic capacity of the wall portions most at risk by around 50%.