Mustafa Kerem Koçkar

Methodology for tunnel and portal support design in mixed limestone, schist and phyllite conditions: a case study in Turkey

Abstract The purpose of this study is to present a methodology for tunnel and support design in mixed limestone, schist and phyllite conditions through investigating two highway tunnel case studies that are located along the Antalya–Alanya Highway in southern Turkey. The main lithologies of the project area are regularly jointed, recrystallized limestone and the weak lithologies of the schist unit (i.e., pelitic schist, calc schist, graphitic phyllite and alternations of these lithologies). A detailed geological and geotechnical study was carried out in the project area, and the tunnel ground support types and categories were determined according to the Q-system, rock mass rating method and New Austrian Tunneling Method (NATM). The shear strength parameters and geomechanical properties of the rock masses were obtained by using the geological strength index (GSI). The deformation moduli and post-failure behavior of the rock masses have been determined. Slope stability analyses were performed at the portal, side or cut slope sections. Kinematic and limit equilibrium analyses incorporating the effects of water pressure were performed for the regularly jointed failed rock slopes. Circular failure analogy was used for the slope stability analyses of irregularly jointed, highly foliated lithologies. Slope support system recommendations were made. A back analysis on a failed slope was performed. The results of the back analysis compared well with the results obtained through the GSI method. The tunnel grounds were divided into sections according to their rock mass classes. The deformations and stress concentrations around each tunnel section were investigated and the interactions of the empirical support systems with the rock masses were analyzed by using the Phase 2 finite element software. The regularly jointed rock masses were modeled to be anisotropic and the irregularly jointed, highly foliated and very deformable soil-like lithologies were modeled to be isotropic in the tunnel finite element analyses.

Engineering geological investigations along the Iliksu Tunnels, Alanya, southern Turkey

Abstract The main objective of this study is to assess the engineering geological characteristics of the rock mass and to suggest appropriate support recommendations along the two autoroad tunnel projects, named as Iliksu 1 and Iliksu 2, which are located along the Antalya–Alanya Highway. The study area consists of pelitic schist and calc schist overlain by a thick sequence of recrystallized limestone and an intercalation of pelitic schist, calc schist and graphite schist. The tunnel ground support types and categories were determined according to the Q-system, Rock Mass Rating (RMR) method and New Austrian Tunneling Method (NATM). Slope stability analyses were performed at the portal and cut slope sections. Kinematic and limit equilibrium analyses incorporating the effects of water pressure were performed for the failed rock slopes. Slope stability analyses of irregularly jointed, highly foliated lithologies were performed using soil slope stability software. The interactions of the tunnel support systems with the rock mass were analyzed through finite element analysis.

Optical Fiber Technology to Monitor Slope Movement

Recently, awareness about hazards caused by landslides and the importance given to the concept of risk management has been continuously increasing. As a consequence, early warning systems have gained much more importance in terms of risk management. Different instrumentation techniques such as inclinometers, tilt meters, extensometers and ground based LIDAR systems have been used to monitor landslides and/or slopes. All these techniques have their own advantages and disadvantages, but the optical fiber system has certain superiority over these methods. Fiber optic based technology serves an incessant process to acquire the data during the monitoring operation, a significant need for such operations and early warning systems. The main objective of this study is to monitor slope movement regardless of lithology and failure types. Equipment utilized in an attempt to accomplish this scope has consisted of a laboratory experimental set-up and an optical fiber system containing Optical Time Domain Reflectometer (OTDR), optical fiber cables and heterocore sensors. A laboratory set-up was constructed to simulate landslide phenomenon and to record movement. The laboratory experiment set-up contains two identical trays filled with soil that posesses an inclination mechanism to represent ideal landslide conditions. The tests show that fiber optical technology can be utilized as a landslide monitoring tool and is useful in determining mass movement throughout a fiber array. These studies are expected to lead risk assessment studies in hazard prone regions and also at the construction and post-construction period of all other displacement dependent engineering projects such as open road cuts.

The use of Ankara Clay as a compacted clay liner for landfill sites

Abstract Because of the current need for new landfill sites in Ankara, the suitability of Ankara Clay as a liner material for landfill sites was investigated. A mineralogical and geotechnical databasewas created by compiling the results of previous tests by the present authors aswell as those of tests performed in the present study. The mineralogical properties of the samples were investigated by X-ray diffraction, scanning electron microscopy and methylene blue adsorption. The cation exchange capacities (CEC) of the samples vary from 12 to 35 meq/100 g soil and the dominant clay minerals are illite, smectite and kaolinite. The geotechnical properties of the Ankara Clay samples that were assessed included specific gravity, the Atterberg limits ( plastic limit, liquid limit, plasticity index), particle-size distribution, compaction properties (i.e. maximum dry density and optimum water content) and hydraulic conductivity. Because the hydraulic conductivity of the samples was lower than the acceptable limit of 1 × 10−9 m/s, it follows that, from a geotechnical perspective, Ankara Clay is a suitable material for use as a compacted clay landfill liner. The relationships between the mineralogical and geotechnical parameters that were investigated by regression analysis indicated that the hydraulic conductivity of the compacted soil samples decreased with increasing plasticity index, clay content, CEC, smectite content, smectite to illite ratio and decreasing illite content. According to the specifications for field construction of compacted clay liners, Ankara Clay is suitable for compaction in the field.

Site characterization of the strong motion stations and evaluation of site effects in the Ankara region during the December 2007 and March 2008 moderate Bala earthquakes

Local site conditions may significantly affect the amplitude and frequency of ground motion during earthquakes. Recordings of recent major earthquakes have demonstrated that soil conditions can generate prominent amplification of ground shaking and can be compared with the amplification predicted by numerical simulation. This study analyzes the ground motion data from the December 2007 and March 2008 moderate Bala earthquake series considering the effect of soil conditions on ground shaking in the southern part of Ankara, the capital city of Turkey. Initially, shear wave velocity profiles of the strong ground motion stations were evaluated to define site classifications for each station in Ankara and its surroundings. Strong motion data collected during the Bala earthquake series (Mw range 5.6–4.8) were used to develop event-specific attenuation relationships for peak ground acceleration and spectral acceleration at various periods and different site conditions. Site amplification factors were derived from the regression results from the event-specific attenuation relationships for the Bala earthquake series. The implications of these ground motion amplification factors were also discussed and compared using the current seismic design codes. Finally, the response spectra from the recording stations were used to determine site amplification factors for different site conditions to evaluate the variability of the site response in localized regions in Ankara.

Characterization and Assessment of Large Landslide Movement Along the Bursa-Inegöl-Bozüyük Highway in Turkey

This study discusses the geotechnical characterization, modeling and stabilization of a large scale landslide that occurred in highly weathered rock during highway construction. The study area is located along the Bursa-Inegol-Bozuyuk highway in Turkey. The mass movement occurred 110 m behind the road cut with 400–600 mm wide tension cracks. Some remediation techniques were applied on site while mass movements were continuing and the size of the tension cracks that were located at the crown reached a width in the order of a meter. A detailed geomechanical and geotechnical site investigation including engineering geological boring, standard penetration test, pressuremeter tests, inclinometer measurements along with laboratory test data was performed at the project site. Detailed engineering geological mapping was performed to document the observed slope movements. In the light of the compiled data, critical profiles were determined and back analysis was performed through comparing the displacement obtained from the inclinometer results and the finite element model. Regarding the back analyses, the site was modeled using coupled slope stability analyses along the most representative profile by considering the landslide mechanism, the parameters evaluated from the geotechnical investigations, the size of the landslide and the location of the slip circle. Since the project site is located in the vicinity of the Eskisehir Fault Zone, pseudo-static and dynamic stability of the site were also evaluated. As a result, the most suitable slope remediation technique was determined to be a combination of surface and subsurface drainage, application of rock buttress at the toe of the landslide and unloading of the landslide material.