The Zelve Open-Air Museum, consisting of three valleys, is one of the oldest historical semi-underground settlements in the Cappadocia Region of Turkey which was designated as a World Heritage Site ...in 1985 by UNESCO. Particularly in the first valley, there are a lot of underground openings of different sizes carved in a soft tuff next to the valley cliffs used for cliff settlement in the past and several antique churches with some geo-engineering problems. In addition, steep natural slopes in this valley are prone to toe erosion resulting in stability problems. In this study, it is aimed to investigate engineering characteristics of the surrounding tuff and factors affecting them, and to assess the effect of rate of toe erosion on the stability of steep valley slopes and structural stability of some selected typical underground openings with large spans subjected to spalling. For these purposes, some observational, experimental and numerical modelling studies were conducted. Experimental results indicate that strength and deformability properties of the weak tuff surrounding the openings drastically reduce when it becomes wet or saturated. This situation suggests that possibility of occurrence of failures is expected to be higher in rainy seasons due to increase in water content of the tuff. Experimental results also suggest that spalling commonly observed in the valley is related with freezing–thawing and wetting–drying cycles in nature and that the process of freezing and thawing accelerates further the degradation of the rock. The long-term measurements at selected locations suggest that erosion in the tuff is important, which increases particularly in winter and spring seasons and results in the loss of support accelerating the occurrence of further slope failures. The 2-D numerical solutions indicate that no significant change in shear and tensile stresses in steep valley slopes prone to toe erosion would be expected after 100years. However, the solutions obtained from the 500- and 1000-year scenarios suggest that failure zones due to the tensile stresses would develop in the form of slabs with thicknesses of 50–60cm and 90–100cm, respectively, which would break off from the slope and fall down. The results from 3-D numerical solutions indicate that failure (yield) zone resulting from tensile stresses around the semi-underground openings will develop parallel to the sidewalls. These results confirm the observed spalling of the tuff in the form of slabs parallel to the walls of the openings.
•Main geo-engineering problems at a historical settlement in soft tuff are described.•Engineering characteristics of tuff affecting historical structures are evaluated.•Slope failure mechanism due to toe erosion is clarified using numerical modelling.•Opening stability is investigated by modelling and compared with observed failure.•The results provide useful information for protection–restoration works in the site.
The eruptive sequence of the 7.6-Ma-old Akdag-Zelve ignimbrite (AZI) eruption comprises five units totalling up to > 50 m on Akdag mountain. They are, in stratigraphic order: (a) the
main pumice fall ...deposit (up to 10 m); (b)
the lower surge series (up to 4 m); (c) the
upper pumice beds (up to 0.8 m); (d) the
upper surge series (up to 5 m); and (e) the
Akdag-Zelve ignimbrite (up to 40 m). The main pumice fall deposit shows a second distal thickness maximum about 20 km from the source, whereas the upper pumice beds form a simple NNE-extending fan. The source area, about 6 km north-northeast of Kaymakli, is inferred from fallout thickness, size and amount of lithic clasts, depositional facies and flow directions of the surge deposits. The main pumice fall deposit encloses accretionary lapilli up to 6 cm in size indicating a steady phreatomagmatic influence on the eruptive style from the very beginning. The major surge sequence beneath the ignimbrite is similar to that of the 1400 yr B.C. Minoan eruption on Santorini, Greece, and resembles the Minoan B stratigraphic unit attributed to phreatomagmatic eruptions due to ingression of seawater into the conduit. Similarly, the depositional environment of marshes and marginal flats of a lacustrine basin in Cappadocia accounts for the external water supply and the generation of surges during the AZI eruption. Estimates of eruption column height of ≥ 45 km indicate that the AZI eruption ranks in the order of the 1956 Bezymianny, 1815 Tambora and the Waimihia Plinian pumice eruption of New Zealand. Volume estimates of the erupted tephra are on the order of 41.5 km
3 for the main pumice and 0.35 km
3 of the upper pumice.
