Mutluhan Akin

Rockfall hazard analysis for an historical Castle in Kastamonu (Turkey)

The Kastamonu Castle located on a sandstone hill with Eocene age is one of the most historical and touristic places in Kastamonu city center. The settlement of the city expanded towards the hill of the Kastamonu Castle and adversely affected by rockfalls in the past. The rockfall problems around the castle could be related to jointing, weathering, freezing-thawing and earthquake effects or a combination. In this study, the rockfall hazard at the castle is evaluated by two-dimensional rockfall analyses along 17 profiles selected in different orientations. Different size of rock blocks and various types of movements are taken into consideration in the analyses. Fall-out distance, bounce height, kinetic energy and velocity of the sandstone blocks are separately evaluated. The obtained data are used to define the possible rockfall hazard zones. Finally, the areas having potential rockfall risks are distinguished. Based on the evaluation of the data, rock bolting after removing of unstable blocks and supporting the area with the protective fences are suggested.

Assessment of rock slope stability by probabilistic-based Slope Stability Probability Classification method along highway cut slopes in Adilcevaz-Bitlis (Turkey)

Rock slope stability is of great concern along highway routes as stability problems on cut slopes may cause fatal events as well as loss of property. In rock slope engineering, stability evaluations are commonly performed by means of analytical or numerical analyses, principally considering the factor of safety concept. As a matter of fact, the probabilistic assessment of slope stability is progressively getting popularity due to difficulties in assigning the most appropriate values to design parameters in analytical or numerical methods. Additionally, the effect of heterogeneities in rock masses and discontinuities on the analysis results is minimized through the probabilistic concept. In this study, slope stability of high and steep sedimentary rock cut slopes along a state highway in Adilcevaz-Bitlis (Turkey) was evaluated on the basis of probabilistic approach using the Slope Stability Probability Classification (SSPC) system. The probabilistic assessment indicates major slope stability problems because of discontinuity controlled and discontinuity orientation independent mass movements. Almost all studied cut slopes suffer from orientation-independent stability problems with very low stability probabilities. Additionally, the probability of planar and toppling failures is significantly high with respect to the SSPC system. The stability problems along the investigated rock slopes were also verified by field reconnaissance. Remedial measures such as slope re-design and reinforcement at the studied locations should be taken to prevent hazardous events along the highway. On the other hand, the probabilistic approach may be a useful tool during rock slope engineering to overcome numerous uncertainties when probabilistic and analytic results are compared.

Evaluation of the Rockfall Potential of Kastamonu Castle Using 3-D Analysis

The Kastamonu Castle is one of the magnificent monuments of the Kastamonu province (Turkey) located on a steep sandstone hill with Eocene age. The surrounding settlement around the castle suffered from numerous rockfall events in the past. Rockfalls after an initial block toppling are controlled by a bedding plane and two joint sets existing in the sandstone. The rockfall potential along the entire castle perimeter was evaluated by means of three-dimensional (3-D) rockfall analyses using the ROTOMAP software. Rockfall initiation was modelled along a detachment line situated just below the castle walls. The results indicate that the maximum run-out distances around the castle exceed the settlement boundary on the western, southern, and eastern sides. The northern part of the castle is less critical due to lower slope gradient. In order to protect the settlement from falling blocks, vital remedial measures are suggested.

Reliability of Shear Strength Parameters for a Safe Slope Design in Highly Jointed Rock Mass

Open image in new window Shear strength parameters of a slope mass are of utmost concern in stability analyses. However, due to sampling difficulties, it is quite challenging to retrieve precise design parameters particularly for the slopes excavated in heavily jointed rock masses. As a matter of fact, a rough estimation of shear strength may lead to slope failures causing catastrophic events. In this paper, a repeating slope failure in highly jointed and deformed metamorphic rock mass threatening the safety of a large-scale reinforced concrete water storage tank in western Turkey is evaluated considering the reliability of shear strength parameters. On site, a series of slope stabilization works were carried out to protect the stability of existing water storage tank on the upper level. Slope stabilization by retaining pile wall failed to stop the failure at first as a consequence of poor structural design and improper assignment of shear strength parameters. Final slope stability was achieved after the placement of a permanent granular buttress. Back analyses using linear Mohr-Coulomb and non-linear Hoek-Brown failure criterion were executed to reveal the shear strength parameters of the chaotic rock mass. The maximum normal stress acting on the sliding surface was found to be around 130 kPa. Non-linear back analyses proposed a GSI value of 21 indicating a blocky and highly disturbed material. High shear strength parameters were found for the highly fractured rock mass after back analysis by the linear Mohr-Coulomb failure criterion. Eventually, it is noteworthy to mention that the shear strength parameters of a failure surface in heavily jointed rock mass are normal stress-dependent and well defined by the non-linear failure criterion.

The Rockfall Potential of the Southwestern Part of Kastamonu Castle (Turkey) Based on 2-D and 3-D Analyses

Urbanization around steep rock slopes with jointed rock masses is mostly under the threat of rockfalls. Numerous catastrophic rockfall hazards have been reported throughout the world due to the downslope movement of detached rocks. It is quite critical to determine the rockfall potential of a location considering rockfall trajectories, run-out distances, bounce heights and the kinetic energies of falling rocks. Therefore, the determination of rockfall paths requires the use of rockfall simulations. In practice, 2-D and 3-D models are most commonly employed during rockfall event modeling. The rockfall trajectories are simulated on a slope profile with X and Y axis in 2-D models, whereas 3-D models encompass a real space with X, Y and Z axis to calculate the rockfall paths. In this study, the rockfall potential of the southwestern part of the Kastamonu Castle, which is situated on a steep sandstone hill, was evaluated on the basis of 2-D and 3-D rockfall analyses using RocFall v.4.0 and ROTOMAP software, respectively. The close vicinity of the Kastamonu Castle, especially the southwestern region, is surrounded by residential houses and these settlements were adversely affected by disastrous rockfalls in the past. Based on 2-D and 3-D simulations, two different preliminary rockfall hazard maps were prepared and rockfall high-risk areas were defined. Both the 2-D and 3-D analyses pointed out that the southwestern part of the castle is under the great danger of rockfalls of which the weight of falling blocks may reach up to 10 tons. Finally, it is concluded that the maximum fall-out distances in 3-D analyses are more remote than those of 2-D analyses in the study area.

Evaluation of the physico-mechanical parameters affecting the deterioration rate of Ahlat ignimbrites (Bitlis, Turkey)

The paper principally focuses on the durability assessment of various stratigraphic levels of Ahlat ignimbrites collected from the eastern region of Turkey. A total of four different ignimbrite types with dissimilar color, texture and particularly welding degree were tested in laboratory. The laboratory tests performed on the ignimbrite specimens indicate that the welding degree as well as the lithic material content mainly controls the strength and capillarity properties of the ignimbrites. In addition, the durability of highly porous ignimbrites strongly depends upon the degree of welding. The effect of several weathering agents on the ignimbrites was evaluated on the basis of decay constant parameter. Accordingly, salt and ice crystallization pressures are a couple of major destructive agents acting within the micropores of the ignimbrites. Conversely, the investigated specimens are relatively durable against cyclic wetting–drying. Statistical evaluations reveal that the pore diameter is the major controlling factor on the deterioration rate of the ignimbrites after specifically recurrent freeze–thaw cycles. Moreover, the dry unit weight of the ignimbrites is more significant than the uniaxial compressive strength considering the deterioration rates during wetting–drying and salt crystallization. A less significant relationship was obtained between pore diameter and salt crystallization decay constant.