Nihat Sinan Isik

Investigation of the soil amplification factor in the Adapazari region

Turkey is located on the highly active Eurasian plate. A very active strike slip fault, the North Anatolian Fault Zone (NAFZ), crosses Turkey from east to west; earthquakes occurred on this fault on August 17, 1999 (Kocaeli) and November 12, 1999 (Düzce). Regional geology and subsoil conditions can significantly change the characteristics of ground motion. For this reason, determining soil amplification during an earthquake, especially for soft soils, is a very important topic for researchers. In this study, one dimensional ground response analyses were performed for selected Adapazari sites using the August 17, 1999 Kocaeli earthquake strong ground motion record with SHAKE2000 software. Soil characteristics and depth to engineering bedrock at the selected sites are different and the observed level of structural damage at these sites during the Kocaeli earthquake was also different. Calculated soil surface response spectrums at these sites were compared with the recommended design spectra of the Turkish Earthquake Code and the Eurocode 8. According to one dimensional ground response analyses, the calculated response spectra of the selected sites exceed the recommended design spectra of the Turkish Earthquake Code and the Eurocode 8. Calculations show that higher amplification ratios occur at higher periods due to soil behaviour. Results of this study indicate that local geological conditions may amplify ground motion at some periods and, due to this amplification, the calculated response spectra may exceed the recommended design spectra. Therefore, it is clear that local site conditions must be considered for earthquake-resistant engineering designs on soft alluvial soil deposits.

A COMPARATIVE STUDY ON THE ACTUAL AND ESTIMATED SEISMIC RESPONSE OF KIRALKIZI DAM IN TURKEY

Kiralkizi Dam, a 120 m high earthfill dam located in Diyarbakir city, Turkey, was shaken by a moment magnitude, M w =4.6 earthquake at an epicentral distance of 8 km, on December 24, 2000, at 13:31 local time. The seismic response of the dam was assessed by using spectral ratios between (i) available crest and foundation records (C/F), (ii) horizontal and vertical components of the recorded motions (H/V), (iii) by performing 2 dimensional finite difference-based seismic response analyses (Flac-2D), and (iv) ID elastic shear beam solutions. First mode of vibration of the dam in the transverse direction by all four methods were estimated in the range of 0.55 to 0.62 second. Similar close agreement was not observed in higher modal periods estimated by H/V technique as compared to the predictions by C/F, Flac-2D, shear beam analysis techniques. Thus, H/V technique was concluded to be useful for the estimation of the fundamental resonance frequency of a soil structure, but not for its higher harmonics as consistent with available limited literature. In the longitudinal direction, natural period of the dam was estimated as 0.28 and 0. 82 second by H/V and C/F techniques, respectively. Such disagreement was explained by (i) differences in the definitions of the estimated periods, (ii) internal impedance contrast of the dam, (iii) contributions of 3D valley effects. Single seismometer record obtained from crest level was found to be inadequate for reliably assessing the response of a dam in the longitudinal direction, and it is recommended to install multiple seismometers both within dambody and the abutments. Last but not least, the results of these analyses were further compared by available accelograms recorded at three earthfill and rocknll dams from Japan. In general, it was concluded that the seismic response of Kiralkizi Dam is comparable and within the prediction ranges of available analyses methods and is consistent with the expected response of a dam this height.

Investigation of factors affecting the dispersibility of clays and estimation of dispersivity

Dispersive soils have caused failure of many slopes and earth fills due to external and internal erosion. This study aims to investigate various factors used for identification of dispersivity and to develop some new approaches for the prediction of dispersivity of clays. To achieve this purpose, physical and index properties, as well as degree of dispersivity of 29 clay samples taken from five different locations in and around the city of Ankara were determined. Various statistical prediction models were used for prediction of new dispersivity classes obtained by weighting ranking method. It was determined that dispersivity classes obtained from physical and chemical dispersivity tests performed on the same clay samples using distilled water were different from each other. In addition, crumb and pinhole tests were performed by using test waters with varying TDS values on five selected samples to find the impact of water chemistry on dispersivity. It is concluded from all dispersivity tests that total dissolved salts (TDS) values and sodium percentage (SP) remarkably affect the degree of dispersivity, and the use of these two parameters give more reliable results for the determination of dispersivity. By considering all these facts and to predict the most reliable dispersivity class, all dispersivity classes obtained from physical and chemical dispersivity tests were reevaluated by a weighted ranking system, and new dispersivity classes were assigned. In order to estimate these new dispersivity classes, various statistical models were established by using results of chemical analysis of pore water of clay samples. For this purpose, prediction models including soft computing methods such as decision tree and logistic regression are used and most reliable prediction models having the highest prediction performance are suggested.

Evaluation of Flexible Highway Embankment Under Repetitive Wheel Loading Using Finite Element Analysis

Within the context of this study, the deformation behaviour of multi layered highway road embankment consist of asphalt concrete supported by the underlying base and subbase layer under repetitive wheel load were analysed using finite element methodology. Plane strain finite element analyses were carried out by using Plaxis software to calculate rutting behaviour of embankment. Asphalt concrete was modelled using linear elastic model whereas hardening soil model with small-strain stiffness (HSsmall) was used to examine deformation behaviour of base, subbase and subgrade layers due to its capability to model stress dependent stiffness, unloading-reloading behaviour and hysteric damping.

Bearing Capacity and pH Value of Stabilized Soils with Class F Fly Ash and Cement

The California Bearing Ratio (CBR) test determines behaviour of road sub-base and granular layers for flexible pavement. In the conventional CBR test, compacted sample was waited in air for 24 h and in water for 4 days. In this study, the fresh and 28 days curing effects were examined and pH values were measured end of 28 days curing on the CBR percent of soils stabilized with F class fly-ash and cement. There are two main matrix material in this study. One of the matrices consists of Bilecik Clay and Lime and other consists of Bilecik Clay, Bentonite and Lime. In samples, fly-ash (Class-F) and cement were used as additives. Different mixtures which were obtained with various combinations of these materials were prepared and end of compaction were cured in various moulds depending on test. The mechanical strength test as wet CBR, triaxial and unconfined strength tests were performed on the mixtures and physical characteristics as CBR percent and chemical characteristic as pH values were measured.

Behavior of Dams Under Earthquake Loading-Case of Lower San Fernando Dam

Soil liquefaction is seen where the water table is high and soil is cohesionless. Especially, it occurs when drainage is not possible or limited. Consequently effective stress decreases as result of increasing pore pressure during shearing. The significant majority of damage of buildings, roads, bridges and dams in earthquakes are due to soil liquefaction. Recently, the importance of soil behavior during the earthquakes has begun to be discussed. In particular, soil liquefaction can cause serious damages to earth—rockfill dams constructed in earthquake prone areas. In 1994-USA, 105 dams were affected within a 75 km radius from center of the Northridge earthquake of 6.7 magnitude. Some of these dams are earthfill and others are rockfill and not all of these dams were in danger of collapse. However, settlement cracks and/or slope movements have been observed. Others did not affected. Besides, many of these dams experienced the San Fernando Earthquake which has a magnitude of 6.5 occurred in the same area. In 1918, the Lower San Fernando Dam having a height of 42 m which was built using “hydraulic fill” technique was heavily damaged. In this study, Lower San Fernando Dam and earthquake loading is modelled using a finite difference program FLAC which contains Finn liquefaction model. At the end of the analysis, damage to the dam section, plastic shear deformations, distribution of pore pressure and deformations are compared with the real case.

Effect of Height and Water Table Level on Stability Analysis of Embankments

Slope stability is one of the important analysis not only human being and economic issues but also environmental and sustainability aspects as well. There are analysis softwares available to search factors of safety calculations as well as stabilization methods. Slide is one of the most comprehensive slope stability analysis software available, complete with finite element groundwater seepage analysis, rapid drawdown, sensitivity and probabilistic analysis, and support design. All types of soil and rock slopes, embankments, earth dams, and retaining walls can be analysed. In this study, effects of groundwater level is investigated in terms of stability analysis of embankments and earth fill barriers. Embankments and earth fill barriers are constructed on soft clay soil materials. Different scenarios and input parameters are used in the analysis. Embankment and earth fill barriers slope, shape and geometries are taken from according to Directorate General of Road Transport Regulation. Factors of safety are very variable due to changing groundwater locations.

Evaluation of Occupational Safety Culture in Construction Sector in the Context of Sustainability

Construction sector is one of the sectors where occupational-work accidents are highest. A way to minimize accident ratio in this sector is to manage the subject of occupational health and safety beyond the legal necessities. In this study, necessary precautions that company management has to take are explained for the development of safety culture in construction sector and they are evaluated.

A new empirical equation proposed for the relationship between surface rupture length and the earthquake source parameters

This study aimed to investigate the effects of magnitude, focal depth and the thickness of the overburden material on the length of the surface rupture caused by an earthquake; and to propose new empirical equations between the surface rupture length and the earthquake source parameters. To accomplish this purpose, a series of tests were carried out in the laboratory utilizing a set up simulating a strike-slip faulting mechanism. In addition to laboratory tests, a database was established from the earthquakes that have occurred in Turkey and all over the world. Consequently, new empirical equations were suggested between magnitude and surface rupture length and focal depth of an earthquake based on the data obtained from the laboratory model tests and real earthquakes.