Determination of behaviour of barrette piles under lateral load in sand

Generally, foundations should meet two conditions. First condition is that the foundations must carry structural loads without failure (ultimate bearing capacity). Foundation must be safe against overall shear failure. Second condition is that the foundation must carry the structural loads without excessive displacements. If the magnitude of structural forces and the soil properties are favorable, shallow foundation can be chosen. If shallow foundations cannot perform these two conditions, then deep foundations are preferred instead. Deep foundations are structural elements which transfer loads through compressible soil and weak soil to underlying stronger layers. Barrettes are a type of deep foundation used to transport structural loads to deeper layers of soil. The design of barrettes are the same as deep foundation design. Basically, barrette piles can be considered as bored piles. While designing barrettes, it should be shown that barrette is safe against overall shear failure in the soil that supports it and barrettes should not undergo excessive settlements. At the present time, there is a growing need for the construction of large scale, such as high towers, wide bridges, subway constructions, airports, seaports, stadiums. In these structures, structural loads can be high. This situation increased the need for deep foundations. Barrettes are similar to bored piles. However, they have more advantages with the same amount of material (rebar and concrete) more bearing capacity is achieved. Resistance of lateral stress and bending moments is better than circular piles of the same section and easily connecting to structures, so that one single pile is sufficient under each column or bearing unit. Another advantage is that barrettes have better mobilization of lateral friction than a circular pile of the same section. Besides, barrettes are preferred because of the ease of application. In addition to the vertical loads from the structures, the effects of lateral loads must also be investigated. Barrettes are formed to carry lateral loads such as wind, earth pressure, water pressure, earthquake, ship impact. Many important information about vertical and lateral load effects were obtained by experiments. To this day, the behaviour of pile foundation under vertical loads have been investigated more broadly than piled foundations under lateral loads. Further investigation is needed to understand the behaviour of lateral loaded piles. In this thesis, after giving information about pile foundation, barrettes which are the subject of the thesis, were explained. Then, brief information about design method was given. Testing apparatus and experimental results of studies are explained. Properties of soil which is used in experiment, were determined by the laboratory experiments. The test set-up for the lateral loaded barrette model piles has been designed and the parts of the system were described in detail. In this study, the effect of lateral load on the barrettes were investigated on 20% and 70% relative density. Experiments were repeated for three types of model piles. Sand was dried for the experiment. The experimental set-up is designed and manufactured. The profiles are manufactured as close as possible to dimensions obtained by reducing the actual pile sections by 1/40. After each model pile placed in the test box, sand placed as loose and dense. For this propose, a device is designed and provided for fixing the profiles in the loading system. Profiles are drilled about 14 mm thickness to the point where they are held and through this hole the shaft of the loading system passes. Sand is filled in the test box every 5 cm by sprinkler method. To do this, inside of the test box and glass are marked at every 5 cm. The weight of sand in each 5 cm layer is calculated, filled and compacted accordingly. After sand filling has been completed, the potentiometer is placed. Potentiometer, strain gauge and load cell are used for measuring displacement amount of unit deformation and the amount of load. These data were transferred and recorded by the data logger. These all devices were checked and calibrated before main experiments. Moment values were calculated from the strains obtained by three strain gauges placed on the model pile. Thus, maximum moments during the experiment were obtained. The experiment was modelled with Plaxis 3D program. Plaxis 3D is a finite element software for three-dimensional analysis of deformation and stability in geotechnical engineering and rock mechanics. This software can be used for excavations, embankments, foundations, tunneling and mining. In recent years, the finite element modeling has been widely used in the design and analysis of soil mechanics and foundation engineering problems. The finite element modeling is a calculation method that can analyze a system's behavior by considering many factors that may affect its behaviour. The main advantage of this method, non-linear stress-deformation behaviour of the soil and this characteristic can be taken into account with material models defining non-linear behaviour characteristic. In this study, Mohr-Coulomb modelling was used for sand in Plaxis 3D. The Mohr-Coulomb model (MC) is a linear elastic and fully plastic model with failure criterion. While modelling sand, model parameters should be found by laboratory tests and should be able to be explained the material behaviour for the stress and deformation properties of the model. Soil and profile properties obtained by the experiments were used in the software and analyzed. Plaxis 3D results were compared with the model experiment results. It was observed that the load-deformation behaviour is consistent with Plaxis 3D. However, the values obtained with Plaxis 3D software are higher. In the case of both loose and dense sand, the lateral bearing capacity values obtained by using computer analysis are greater than the experimental values. The results from experimented studies and three dimensional non-linear finite element are affected by pile cross sections. Model square cross-section profile is selected close to bored pile dimensions. Other two profiles represent barrette pile. As a result, it has been seen that both bearing capacity and moment bearing capacity of the barrette section models are higher for '+' profile both in Plaxis 3D and laboratory experiments. The results are similar in square sections and rectangular section. The effect of relative density on the bearing capacity is higher than the effect of stiffness of the pile on bearing capacity.