Secondary toppling failure analysis and optimal support design for ignimbrites in the Ihlara Valley (Cappadocia, Turkey) by finite element method (FEM)

Abstract

Kizilkaya ignimbrite, characterized by a blocky structure in the Ihlara Valley (Cappadocia, Turkey), poses many hazards to visitors and the human-made churches and dwellings carved in the valley slopes. The instability mechanism in the valley should be carefully investigated to determine and implement a suitable prevention method. For this purpose, the finite element method (FEM) models were developed in RS2 software to illustrate the problem of progressive failure in the valley's cliffs. A simple geometry represented the rock strata and its surroundings. The effect of columnar structure on the cliff stability was mimicked as a jointed medium in two-dimensional numerical models. The results of FEM models revealed that as the stage of failure progresses in the slope, the strength reduction factor decreased subsequently from 2.05 to 0.45. These models correctly captured the prevailing failure mechanisms observed in the valley slopes. Depending on the size of the rock blocks described in the FEM analysis, an effective support system was proposed to remedy the slope failure. It was found that fully bonded rock bolts with a length of at least 2.5 times the width of a typical block should be implemented with a certain grid pattern. The study clearly showed that it was promising to realize a numerical solution to secondary toppling failure in a jointed rock mass using the FEM.