ABSTRACT THE EFFECT OF GROUP BEHAVIOR ON THE PULL-OUT CAPACITY OF SOIL NAILS IN HIGH PLASTIC CLAY Ak&amp / #56256 / &amp / #56533 / &amp / #56256 / &amp / #56570 / , Ebru Ph. D., Department of Civil Engineering Supervisor : Assoc. Prof. Dr. B. Sad&amp / #56256 / &amp / #56533 / k Bak&amp / #56256 / &amp / #56533 / r Co-Supervisor : Asst. Prof. Dr. M. Tolga Y&amp / #56256 / &amp / #56533 / lmaz September 2009, 161 pages Soil nailing technique is widely used in stabilizing roadway and tunnel portal cut excavations. The key parameter in the design of soil nail systems is the pull-out capacity. The pull-out capacity of the soil nails can be estimated from the studies involving similar soil conditions or can be estimated from the empirical formulas. Field verification tests are performed before the construction stage in order to confirm the parameter chosen in the design of soil nailing system. It is reported in the literature that, the pull-out resistance of a soil nail in sand should be reduced for the nails installed closer than a specific minimum distance, whereas no such requirement have been discussed for nail groups in clays. v In this study, the pull-out resistance of nails in high plastic clay are tested to investigate the influence of nail spacing in group applications. The laboratory set-up for the pull-out tests is composed of an aluminum model box (300mm (w) x 300mm (h) x 500 mm (l)), soil sample, reinforcements, pull-out device, overburden pressure applicator and monitoring device. A series of pull-out tests has been carried out on single nails and group of nails with spacings 2 and 6 times the diameter of a nail in order to observe the group effect on the pullout capacity of the nails. The nails are located into their positions during the placement of clay into the box. Within the limitations of this study, it is observed that, there is a reduction in the pull-out capacity of the central nail in 2&Oslash / spaced group. The pull-out capacity of the central nail in nail group with 6&Oslash / spacing, is not affected from the neighboring nails. In all tests, the plots of pull-out load on nail versus nail displacement show that, the peak value of load is followed by a sharp reduction. The peak pull-out load is mobilized at first few millimeters of the nail displacements. A 3D finite element program is used for numerical analyses of the experiments. The measured pull-out capacity of the soil nails are compared by the results of simulated forces obtained from these analyses. By and large, the agreement between the tests and the numerical analyses is observed to be satisfactory. The details of the numerical models are briefly presented in order to give insight into numerical modeling of soil nails in real applications.

This dissertation thesis deals with the improvement of computational approaches for prediction of residual stresses in welded joints of welded structures in order to ensure greater compliance of the calculated results with the real conditions of welding and heat treatment. The improvement of computational approaches is based on application of elastic-viscoplastic material models which are able (compared with elastic-plastic material models) to take into account the viscoplastic processes ongoing during welding and heat treatment. This leads to more accurate calculated results which enter into further assessment of limit states and directly decide on the safety and lifetime of welded structures. Performed computational and experimental works, confronted with results published in the world, confirm the influence and benefit of application of elastic-viscoplastic material models in the frame of welding and heat treatment numerical analyses. Therefore elastic-viscoplastic material model is further applied in solution of practical project solved by IAM Brno. Solution of this project, whose aim is the development of repair of dissimilar metal welds (without post-weld heat treatment) in Dukovany and Temelin nuclear power plants using "Weld overlay method", has confirmed that application of elastic-viscoplastic material model leads to more accurate calculated results. For this reason the elastic-viscoplastic computational approach will be included into all future tasks of IAM Brno.

Geosynthetic reinforced soil (GRS) is a soil improvement technology in which closely spaced horizontal layers of geosynthetic are embedded in a soil mass to provide lateral support and increase strength. GRS is popular due to a relatively new application for bridge support, as well as long-standing application in mechanically stabilized earth walls. Several different GRS design methods have been used, and some are application-specific and not based on fundamental principles of mechanics. Because consensus regarding fundamental behavior of GRS is lacking, numerical and mathematical analyses were performed for laboratory tests obtained from the published literature of GRS under triaxial compression in consolidated-drained conditions. A three-dimensional numerical model was developed using FLAC3D. An existing constitutive model for the soil component was modified to incorporate confining pressure dependency of friction angle and dilation parameters, while retaining the constitutive model's ability to represent nonlinear stress-strain response and plastic yield. Procedures to obtain the parameter values from drained triaxial compression tests on soil specimens were developed. A method to estimate the parameter values from particle size distribution and relative compaction was also developed. The geosynthetic reinforcement was represented by two-dimensional orthotropic elements with soil-geosynthetic interfaces on each side. Comparisons between the numerical analyses and laboratory tests exhibited good agreement for strains from zero to 3% for tests with 1 to 3 layers of reinforcement. As failure is approached at larger strains, agreement was good for specimens that had 1 or 2 layers of reinforcement and soil friction angle less than 40 degrees. For other conditions, the numerical model experienced convergence problems that could not be overcome by mesh refinement or reducing the applied loading rate; however, it appears that, if convergence problems can be solved, the numerical model may provide a mechanics-based representation of GRS behavior, at least for triaxial test conditions. Three mathematical theories of GRS failure available in published literature were applied to the laboratory triaxial tests. Comparisons between the theories and the tests results demonstrated that all three theories have important limitations. These numerical and mathematical evaluations of laboratory GRS tests provided a basis for recommending further research. / Ph. D. / Sometimes soils in nature do not possess the strength characteristics necessary to be used in a specific engineering application, and soil improvement technologies are necessary. Geosynthetic reinforced soil (GRS) is a soil improvement technology in which closely spaced horizontal layers of geosynthetic material are placed in a soil mass to provide lateral support and increase the strength of the reinforced mass. The geosynthetic materials used in GRS are flexible sheets of polymeric materials produced in the form of woven fabrics or openwork grids. This technology is widely used to improve the strength of granular soil to form walls and bridge abutments. Current design methods for GRS applications are case specific, some of these methods do not rely on fundamental principles of physics, and consensus regarding the fundamental behavior of GRS is lacking. To improve understanding of GRS response independent of application, the three dimensional response of GRS specimens to axisymmetric loading were investigated using numerical and mathematical analysis. A numerical model using the finite difference method in which the domain is discretized in small zones was developed, and this model can capture the response of GRS laboratory specimens under axisymmetric loading with reasonably good accuracy at working strains (up to 3% strain). This numerical model includes a robust constitutive model for the soil that is capable of representing the most important stiffness and strength characteristics of the soil. For large strains approaching failure loading, the numerical model encountered convergence difficulties when the soil strength was high or when more than two layers of reinforcement were used. As an alternative to discretized numerical analysis, three mathematical theories available in the published literature were applied to the collected GRS laboratory test data. These evaluations demonstrated that all three theories have important limitations in their ability to represent failure of GRS laboratory test specimens. This study is important because it proposed a numerical model in 3D to represent the GRS behavior under working strains, and it identified several limitations of mathematical theories that attempt to represent the ultimate strength of GRS. Based on these findings, recommendations for further research were developed.