Browsing by Author "Orhan, Ahmet"

Now showing 1 - 2 of 2

A Comparative Study on Rockfall Block Motion Characteristics Using 3-D and 2-D Rockfall Simulations: a Case Study From Cappadocia (Mazı, Türkiye)
(Springer, 2025) Akin, Mutluhan; Dincer, Ismail; Orhan, Ahmet; Varol, Oguen Ozan
Within the scope of this research, rockfalls in Maz & imath; village of & Uuml;rg & uuml;p (T & uuml;rkiye) district were simulated on a digital surface model constructed using high resolution (2.9 cm) point cloud data retrieved from a real orthophoto mosaic gathered by an unmanned aerial vehicle in order to compare the results of 2-D and 3-D rockfall models. At the initial stage, 3-dimensional rockfall analyses were carried out using RocPro3D software and block dynamics such as trajectory, maximum runout distance, bounce height and total kinetic energy of the blocks were determined. Subsequently, a total of eight slope profiles were obtained from the point cloud data and 2-dimensional rockfall analyses were executed by means of RocFall 2-D software. Using a rockfall point source indicating the starting position of 2-D rockfall analysis, the rockfall analyses were repeated on 3-dimensional digital surface model and the block motion characteristics obtained from 2-D and 3-D analyses were compared. Eventually, it is revealed that block runout distances may differ in 3-D and 2-D rockfall analyses. Additionally, 3-D analyses reveal a significant advantage over 2-D analyses in terms of including topographic roughness, curves and obstacles in the model. On the other hand, one of the most significant variances between 2-D and 3-D rockfall analyses retrieved in this research is in the bounce height values. While the bounce height value in 2-D models may attain a maximum of 7 m, 3-D simulations point out that the detached blocks mostly roll over the slope with very low bouncing. When the simulation results are evaluated in terms of total kinetic energy, it is concluded that kinetic energy values are commonly higher in 2-D rockfall analyses than those of 3-D simulations. Conversely, block translational velocity values are typically comparable in both 2-D and 3-D rockfall models. Besides, considering the trajectories obtained via 3-D rockfall models for the study site, it is obvious that the settlement is under the risk of rockfall to a significant extent. Rockfall simulations highlight that the total kinetic energy values of the blocks are also quite high, which increase the destructive effect of rockfalls.
A New Quantitative Welding Degree Classification for Ignimbrites
(Springer, 2023) Akin, Mutluhan; Topal, Tamer; Dincer, Ismail; Akin, Muge K.; Ozvan, Ali; Orhan, Ahmet; Orhan, Ayse
As a pyroclastic rock type, ignimbrites may reveal varying degrees of welding depending on the temperature (> 535 celcius) and overburden pressure conditions during its formation. The welding degree of ignimbrites increases as the formation temperature and the thickness of the overburden deposit in the depositional environment escalate, which are the most crucial factors controlling the rate of welding in ignimbrites. With the increasing temperature, plastic deformation is observed in ignimbrites and the glassy minerals are being welded. Furthermore, the thickness of the overburden causes the deformation of the ash matrix in ignimbrites at the lower sections and the pumice grains are flattened at different rates. An increase in the degree of welding of ignimbrites causes an improvement in the physical and mechanical properties of the rock material as well. Within the scope of this research, petrographical, mineralogical, and geochemical studies were carried out on a total of 16 different ignimbrite types, which have different color and texture properties, obtained from three different regions of Turkey (Kayseri, Nevsehir, Ahlat) where ignimbrites extensively crop out, and the physical and mechanical properties of these samples were revealed. Consequently, a new welding classification was developed for ignimbrites considering the uniaxial compressive strength and dry unit weight. The proposed welding classification consists of six classes ranging from non-welded to highly welded. When the welding degrees of the selected ignimbrites are evaluated, Kayseri ignimbrites mostly exhibit moderate welding characteristics. Nevsehir ignimbrites, on the other hand, have a low welding degree whereas the degree of welding in Ahlat ignimbrites may vary from low to high. Additionally, long and short axis lengths of pumice grains in the ignimbrite specimens were determined by measuring under the microscope, and shape ratios were determined by different shape parameter evaluation methods. As a result, it has been concluded that the pumice grains in Kayseri and Ahlat ignimbrites have a more lenticular structure than the pumice grains in Nevsehir ignimbrites. Eventually, the welding degree classes of ignimbrites and the classification developed by using threshold values of the oblateness ratio (OR) values of pumice grains at different welding degrees are quite compatible. The proposed welding degree classification is of great importance in the selection of ignimbrites widely used as dimension stone and in terms of engineering classification of this rock type as well as it will guide to the scientific studies to be performed on ignimbrites with varying physical and mechanical properties.