Stability Assessment of Avanos Underground Congress Centre (Cappadocia, Turkey) in Soft Tuffs Through an Integrated Scheme of Rock Engineering Methods

The Cappadocia Region is one of the seven sites in Turkey included in the World Heritage List in 1985 by the United Nations Educational, Scientific and Cultural Organization (UNESCO) and includes structures carved into thick and soft tuffs that have survived and kept their integrity for a number of centuries. Besides existing ancient structures, new underground constructions have been undertaken. Considering the historical characteristics of the region, the construction of an underground structure was planned by the Municipality of Avanos Town to utilize a hill remnant from an abandoned quarry as an underground congress centre in the 1980s, but its construction has not yet been completed due to financial problems. In this study, integrated experimental, analytical and numerical analyses and an in situ monitoring program were undertaken to assess the stability conditions of the congress centre, which was carved into a soft tuff susceptible to long-term degradation processes. The experimental results indicate that the surrounding rock is quite vulnerable to cyclic freezing–thawing and wetting–drying processes. The strength of the rock is drastically reduced under saturated conditions, and the processes of freezing and thawing further accelerate the rock degradation under such conditions. Simple short-term stability analyses clearly show that some tensile cracking may take place and that the opening may suffer from some cracking problems 28–30 years after excavation. The analyses carried out for the long-term safety of the structure indicate that the most critical condition exists for the widest opening and that some supports at the middle of the widest opening may be necessary. Nevertheless, further studies on the long-term characteristics of this tuff are necessary to check this conclusion. The in situ monitoring clearly showed that some further crack propagation will occur, especially after rainy and freezing–thawing periods.