Numerisk modellering av deformationer i ett modellförsök på torv
Sammanfattning: There are limitations in the knowledge of peat in terms of the material's properties and how peat deforms and therefore research in the area is necessary. Peat is common over large parts of Sweden. There are different ways of classifying peat, usually into low, medium and high decay peat where the difference between these three types of peat is the decomposition of the plant fibers. In a highly decomposed peat, there are fewer fibers in comparison to a low-decayed peat. The fibers in the peat can be compared to reinforcement in soil, the fibers in the peat improve the material capacity to take tensile stresses and provide increased strength. Program based on the finite element method, FEM-programs, are used to conduct advanced numerical computations. Plaxis 3D is designed to analyze various geotechnical constructions and load cases. For example, computations can be made on settlements or stability by analyzing stresses and deformations. The computations can be done for both soil and rock material. By studying peat's behavior through numerical simulation of an actual laboratory model experiment, the aim is to increase the understanding of the peat and its mechanical properties when it is loaded and deformed. The purpose of this study was partly to analyze and produce reasonable parameter values for the peat material used in the model tests and partly to compare the results with the experimental results through numerical simulations of different load cases. Displacements (deformations), pore water pressure and loads have been studied and the results of numerical simulations and experimental observations have been compared. The material studied in this work is a low-decomposed peat which in the model tests has been loaded through a consolidation phase and then a shearing phase until the peat has reached a deformation of approximately 200 mm. The sample is first loaded through pre-consolidation and then by a constant vertical deformation rate with a velocity of 45 cm/h. The simulations of the box modeled by using FEM have two different dimensions. The smaller box has the dimensions 1.0x0.5x0.25 m and the larger box has the dimensions 8.0x2.0x0.25 m. The purpose of the different dimensions was to see if the size of the box had any influence on the result regarding the deformations. The results of the simulations was finally compared with the results from SGI's experimental laboratory tests. The simulations performed in this study is a good first attempt to model the experiments. Parts of the results agree with what is obtained in the experimental laboratory tests. The finite element model can be developed and improved further regarding, for example, simulations of permeability and pore water pressure.
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