This thesis deals with numerical simulation of earth pressure against tubular bridges in the software Plaxis. Plaxis is a FEM (Finite Element Method) software based on numerical calculations for which approximate solutions are developed through an iterative process. The program is specifically designed for soil and rock mechanical tests, such as voltage and deformation calculations in soil.The Royal Institute of Technology conducted in 2005, field tests on tubular bridges of corrugated steel, which was part of Ersa Bayoglu Fleners PhD (Bayoglu Flener, 2009). She studied how two different tubular bridges deformed during installation and filling. Tests and measurements were made during filling. The location of the construction and measurements of tubular bridges was a field in Järpås, Lidköping. The company responsible for the production of the tubular bridges was ViaCon AB.This thesis is based on these measurements. Inspiration has also been the newspaper article, "Earth Pressure on an Integral Bridge Abutment: A Numerical Case Study" by Muir, and Nash (Wood & Nash, 2000) which describes how compaction can be simulated in the FEM program. With the above as a starting point, the numerical simulations were carried out.The voltage increase that occurs when the soil is packed has been simulated in the constitutive models Mohr Coulomb, Hardening Soil model in Plaxis from the article by Wood & Nash (2000). The article by Muir Wood and Nash & Nash, 2000) described a recipe procedure, where compaction was simulated by imposing an external weight on the fill which then seemed the same. In the next calculation step, the earth was removed, a new fill was imposed and the calculation was carried out. In the subsequent calculation step, the load was re-imposed. Calculation steps were repeated until the desired fill level was achieved, i.e. The tubular bridge was completely covered. The tubular bridge's deformation during filling was studied. The early filling stages deformed the tubular bridge's head upwards. Deformation proceeded until filling reached the crown. Then there was a downward deflection. The results of shell deformation were then compared against Fleners studies as well as previous, similar numerical calculations performed by Segovia (Segovia, 2006).The results obtained during the numerical analysis were greatly underestimated. The shell deformed to the same extent as in the real field measurements. The deformation patterns corresponded to each other during the filling phases, but when the fill had reached the top of the head, the calculations began to diverge from the deformations in the numerical analysis. This is in contrast to field measurements where the deformation continued. In a comparison between Segovia and this study the results are not so very different, even though the deformations in this study are slightly smaller than those in Segovia's study. The difference in results may be due to the tubular bridges construction in Plaxis. The tubular bridge in this study was made based on sketches from ViaCon AB using the tunnel feature in Plaxis. One reason for the deformations are kept may be due to Plaxis' overestimate of the earth's rigidity and that the response from the simulated gasket fails.Finally, we studied the constitutive models' input parameters to see which parameter had the greatest impact on the tubular bridge's deformation at and around filling. The results from the parametric study were difficult to interpret. Although input data was varied, there was not any significant variation in results regarding the shell deformation. No parameter stuck out from the crowd. This shows how important it is to select an input that reflects what is to be simulated.
| Identifer | oai:union.ndltd.org:UPSALLA1/oai:DiVA.org:kth-51338 |
| Date | January 2011 |
| Creators | Nilsson, Magnus |
| Publisher | KTH, Jord- och bergmekanik |
| Source Sets | DiVA Archive at Upsalla University |
| Language | Swedish |
| Detected Language | English |
| Type | Student thesis, info:eu-repo/semantics/bachelorThesis, text |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess |
| Relation | Examensarbete Jord- och bergmekanik, 1652-599X ; 11/07 |
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