Seyhan Firat

The effectiveness of wave barriers on the dynamic stiffness coefficients of foundations using boundary element method

A comprehensive numerical investigation has been carried out to indicate the influence of wave barriers on the complex dynamic stiffness coefficients of the surface supported foundations under dynamic loads. In the considered problems the underground is regarded as an elastic homogeneous half-space and as a layer on the top of a rigid bedrock. The results of the present numerical simulation are obtained by using the substructure approach in the frequency domain which is formulated on basis of the boundary element method (BEM). The validations of the numerical results are shown through comparison with published numerical data. The results point out that using an open trench barrier with appropriate distance surrounding the vibration source, a notable reduction level can be achieved.

The evaluation of impedance functions in the analysis of foundations vibrations using boundary element method

The basic step in the substructure approach based on discretization of the soil medium for the soil-structure interaction problems is to determine the impedance functions which are defined as the complex dynamic-stiffness coefficients of the soil-footing system are used in the analysis of foundations vibrations. In this study, the discrete values of impedance functions over wide ranges of frequency-factors are presented for both surface-supported and embedded foundations. The numerical results are obtained by using the substructure approach in the frequency domain which is formulated on basis of the Boundary Element Method derived from the fundamental solution for a homogeneous, isotropic and linear-elastic continuum. To further demonstrate in practical applications and to show the solutions of this type of problems to civil engineers, a comprehensive parametric analysis and systematic calculations are performed with various controlling parameters to evaluate the dynamic response of the vibrating soil-foundation system. In addition, the solutions for normalized stiffness and damping coefficients of foundations in almost all cases of vibration modes are in very good agreement with the published results based on the analytical methods. The obtained numerical results should enable practicing engineers to take into account the linear soil-structure interaction problems over wide ranges of frequency factors.

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.

Lateral load estimation from visco-plastic mud-flow around cylindrical row of piles

In this paper, the influence of slow and creeping flow of mud/slurry is modelled as a visco-plastic fluid around cylindrical row of piles. The study is carried out theoretically using principles of applied fluid mechanics. The research initiates from actual requirement in using a series of piled columns as barrier(s) to stabilise such slopes considered to be at risk of land-slide due to reduced stability. It was thought that in the event of slope failure, the homogenised behaviour of the moving mass could be modelled as a fluid with appropriate inertial and mechanical properties. Parametric studies were carried out to estimate forces on a row of piles, considering visco-plastic fluids with different mechanical properties. The analysis focused on determining the variation of force per a unit distance with depth on piles, under the influences of a number of key parameters.

Effect of curing time on selected properties of soil stabilized with fly ash, marble dust and waste sand for road sub-base materials

The properties of sub-base filling materials in highway construction are essential, as they can determine the performance of the road in service. Normally, the existing materials are removed and replaced with new materials that have adequate load-bearing capacity. Rising environmental concern and new environmental legislations have made construction professionals consider other methods. These methods include stabilizing the existing materials with other additives to improve their performance. Additives can be waste materials generated by different industries. In this work, the existing excavated soil is stabilized with waste materials. The wastes consisted of fly ash, marble dust and waste sand. The percentage addition of waste materials was 5%, 10%, 15% and 20% (by mass) of the existing soil. The soil/waste specimens were cured for 1, 7, 28, 56, 90 and 112 days before testing. Testing included the dry unit weight and unconfined compressive strength (qu) as well as X-ray diffraction analysis and scanning electron microscopy observation. Also, the California Bearing Ratio values were obtained and are reported in this investigation. The results showed that the qu values increased with the increase in waste materials content. Also, there is tendency for the dry unit weight to increase with the increase in waste materials.

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.

Performance of Steel Slag and Fly Ash Added Soil as Subbase Materials

The steel industry, which is an indicator of the developed countries with its production, also brings the problem of waste together. This waste product, that differs depending on the production process and is called slag, is generally referred as solid waste. Many researchers to use for different purposes are examining this type of wastes, which are difficult to store and dispose. It is also investigated about the usability as a filling material in civil engineering. The possibility of using such materials as an alternative to soil stabilization solutions, especially in the areas close to the industries producing these wastes, in the filling of such structures as the roads, railways, airport runways comprise of the basis of the surveys. In this study, the impact of steel slag and fly ash, another waste product released because of combusting lignite coal with low energy at the power plants, on the bearing ratio after blending with kaolin grade clay at different rates was observed. Keeping the 5% clay rate stable in weight, steel slag and fly ash with varying rates were added to prepare the test samples, which were cured for 0, 7, 28 and 56 days under stable conditions and subjected to California Bearing Ratio tests. The results showed that when steel slag and fly ash are used with clay, there were significant increases in their bearing ratios compared to the reference clay sample. While the wet California Bearing Ratio (CBR) was around 15% for the normal clay sample, when it is blended only with steel slag the wet CBR increased up to 70%, and when blended with fly ash the wet CBR went up to 130%. The used materials had very weak and weak binding properties when used alone while their binding properties increased by gaining pozzolanic property within the mix.

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.