A Comparison of Local Site Conditions with Passive and Active Surface Wave Methods

This study encompasses dynamic soil characterization and seismic hazard mapping of the Plio-Quaternary and especially Quaternary alluvial sediments of the Çubuk district and its close vicinity that is situated towards the north of Ankara. The project site is located at a region which has a potential of being seriously affected by a possible earthquake occurring along the Çubuk Fault Zone that is thought to be a continuation of the Dodurga Fault Zone and a sub-fault belt of the North Anatolian Fault System that is one of the most prominent fault systems in Turkey with significant earthquake potential. Non-invasive seismic methods were used to obtain a 1-D shear wave velocity profile of the subsurface at 41 sites and two measurements were taken at each site for passive and active surface wave methods. The Multichannel Analysis of Surface Wave Method (MASW) and the Microtremor Array Method (MAM) were used as active and passive surface wave methods, respectively. By combining these two techniques, the shear wave velocity profiles of the sites were obtained. Based on the results, site classes were assigned for seismic hazard assessment studies followed by a preparation of a seismic zonation map of the site utilizing GIS software

Assessment of kinematic rock slope failures in Mudurnu Valley, Turkey

Slope instabilities are one of the most frequent natural hazards capable of causing severe failures both at regional and large scales. Mudurnu, which is settled on a steep valley, is affected by regional rock slope instabilities. These instabilities constitute a hazard and create an important risk to the community since they threaten human lives, settlement areas, and historically-important structures. In order to minimize the hazard and risk associated with slope instabilities, rock masses along the valley were characterized and the potential failure mechanisms were defined. The west side of the valley, which is the focus of the research, is characterized by Cretaceous pelagic discontinuous limestone, and is prone to complex failures. The aim of the study is to characterize the rock mass along the valley, divide the area into geomechanically-uniform sectors, define possible modes of failure (kinematics) and ultimately quantify the potential failure (kinetics) and the associated risk. For the study, in addition to the field work and scan-line survey measurements, an Unmanned Aerial Vehicle (UAV) was utilized to collect high-resolution images from problematic locations that were not accessible. Then, a point cloud of the area was generated. The images were interpreted and the resulting structural representation of the rock mass was compared with information gathered from the scan-line survey in the field. Afterwards, it was used to identify the possible modes of failure along the valley. Since seismic activity in the area is significant due to the proximity of the North Anatolian Fault Zone (NAFZ), which is the most active fault system in Turkey, dynamic loading was also considered for the stability analyses

Ankara'nın batısındaki Geç Pliyosen ve Kuvaterner zeminlerin mühendislik jeolojisi ve jeoteknik karakterizasyonunun yapılması ve sismik tehlike değerlendirmelerinin belirlenmesi.

The purpose of this study is to assess the engineering geological and geotechnical characteristics and to perform seismic hazard studies of the Upper Pliocene and Quaternary deposits located towards the west of Ankara. Based on a general engineering geological and seismic characterization of the site, site classification systems are assigned for seismic hazard assessment studies. The objective of the research is to determine the regional and local seismic soil conditions, predominant periods and ground amplifications, and to idealize the soil profile of the sites by the aid of surface geophysical methods. These studies are combined and integrated with the geotechnical database from a variety of in-situ and laboratory studies that are compiled from present and previous studies regarding the project area and then transferred to an analytical environment for creating relevant information for our site. Then, engineering geological and geotechnical seismic characterization along with seismic zoning map preperation is accomplished. Finally, based on a general engineering geological and geotechnical site characterization, site classification systems are assigned to account for site effects in seismic hazard assessments along with the assessment of mitigation and remediation of seismic hazards.Ph.D. - Doctoral Progra

Evaluation of a sand bentonite mixture as a shaft/borehole sealing material

The mechanical and hydrological characteristics of compacted sand bentonite mixtures with bentonite contents ranging from 5 to 40% were investigated in the laboratory in order to assess their use as a waste isolation material and to select an optimum sand bentonite mixture. Laboratory tests included compaction, compaction permeability, unconfined compression and direct shear tests which led to a recommendation to select a mixture with a bentonite content of 30% for the isolation of underground geological waste disposal repositories. This study complements the previous studies of the authors of this manuscript by determining the mechanical and hydrological properties of sand bentonite mixtures that possess bentonite contents > 30% to determine the geotechnical properties (i.e., unconfined compressive strength, Young's modulus, cohesion and angle of internal friction) and the mechanical behavior of these relatively high levels of bentonite mixtures for the first time in the literature

Tunnel and portal stability assessment in weak rock

The purpose of this study is to present an algorithm for tunnel and portal support design in weak rock conditions. Basic principles of engineering design are introduced and the main stages of the design process are delineated through assessing a highway tunnel case study in Turkey. This case study involved the investigation of the engineering geological and geotechnical characteristics of the rock material and rock mass of the tunnel grounds; evaluation of the field stresses, the applied loads and the deformations around the underground excavations; assessment of the validity of decision making (i.e., alternative selection); and finally, suggesting appropriate support and stabilization techniques for optimum tunnel design

Design of anchorage and assessment of the stability of openings in silty, sandy limestone: a case study in Turkey

This study presents a procedure for the design of anchorage and for the assessment of the stability of openings in silty, sandy limestone through investigating the geotechnical problems of the Hasankeyf historical settlement area in southeastern Turkey, of which a good portion will stay below the reservoir of the proposed Ilisu dam. Rock mass characterization was performed. The RMR and GSI methods were utilized for rock mass classification. The RocLab software was used to determine the shear strength parameters and the geomechanical properties of the rock mass according to the GSI method. The cohesion and angle of internal friction of the rock mass was determined as 257 kPa and 52degrees, respectively. A back analysis was applied to a structurally controlled planar failure block supporting one of the prominent historical structures in the area to determine the shear strength parameter pairs that satisfy limit equilibrium along the sliding surface of the planar block. A sensitivity analysis of the most likely shear strength pairs satisfying limit equilibrium was performed as a function of reservoir water condition (i.e., rapid drawdown, dry and wet reservoir condition) and the expected earthquake generated peak horizontal ground acceleration coefficient. The results of the back analysis led to a cohesion of 161 kPa and an angle of internal friction of 40degrees along the failure surface of the planar block. A limit equilibrium sensitivity analysis of the unstable rock block was performed as a function of the water condition of the reservoir, expected earthquake generated peak horizontal ground acceleration coefficient and rock anchor inclination angle. The minimum anchor force required for the stabilization of the planar block was calculated for a rapid drawdown condition as 4000 kN/m. A total of fifty six (56) rock anchors, each with a service load capacity of 1000 kN and spaced at I in are recommended for stability. Finite element analysis was utilized to analyze the collapse of some of the roofs of the adjacent man-made cave dwellings carved in rock due to insufficient pillar thicknesses and to determine the minimum pillar thickness required between adjacent caves in the region for stability. Nine different pillar thicknesses ranging from 0.1 to 0.93 m were analyzed. The stages included in the finite element analysis of the caves were: (a) gravity loading due to the thickness of the overburden followed by applying the far field horizontal stresses and inserting the planar block fracture; (b) excavating the caves in stressed rock assuming full face excavation and (c) applying a uniform traction load. The results of the finite element analysis led to a recommendation to apply a steel arch support to one of the adjacent caves located at Hasankeyf in case the wall thickness was less than or equal to 0.5 m

Evaluation of Site Characterizations and Site Effects of the Ankara Basin Turkey

The purpose of this study is to assess the in-situ site characteristics and to perform seismic hazard studies of the Upper Pliocene to Pleistocene fluvial and Quaternary alluvial and terrace deposits located towards the west of Ankara. Based on a general engineering geological, geotechnical and seismic characterization of the site, site classification systems were assigned for seismic hazard evaluations. Then, short-period noise recordings of the microtremor measurements at the ground surface have been used to estimate the site response of the site. This research mainly focuses on the development of a methodology to integrate the various components necessary for a regional multihazard seismic risk assessment that includes consideration of hazards due to local site effects. These tasks have been fulfilled through the development of an engineering database that was obtained from invasive and non-invasive explorations at the study area. Hence, the engineering geological and geotechnical site characterization studies have been compiled; and geophysical site characterization studies have been performed, particularly in the Quaternary sediments of the Ankara basin. By using all of these studies, hazard assessment maps (i.e., site classification map and site period map) and a seismic zonation map of Ankara basin, Turkey were developed along with discussing the consequences of the seismic hazards

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

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