Evaluation of the Efficiency of the Standardized Norrland Method: Analyses with the finite element program PLAXIS on the case of road 685 Vibbyn - Skogså, Boden municipality
Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
Road 685 between Vibbyn and Skogså in the Boden municipality has, due to large quantities of sulphide soil and a nearby creek, been subjected to large settlements over the years. Trafikverket allowed for a reinforcement of the road with the settlement reducing method light embankment piling (also known in Sweden as the Norrland method), where a pile group consisting of trunks is driven down into the underlying soil, on which the road embankment will rest. A geogrid is laid in the lower part of the road embankment to stiffen the embankment material, but also to create a more stable arching between the piles. There have however been a few questions regarding at what degree the geogrid grants these effects, and Trafikverket allowed, with the help of Edlund et al. (2015), for finite element computations in 2D. The investigation showed that 1.2 m pile spacing, as used on road 685, is too narrow for the geogrid to have an impact on the settlements.With this in mind, the question arouse at Trafikverket if the newly standardized triangular piling pattern truly is superior to the former, square, pattern (which was used on road 685). Within this work a number of simulations were done in the finite element program PLAXIS, based on the work by Edlund et al. (2015), of the road embankment on road 685 with both triangular and square pile group patterns. The simulations were mainly done in 3D, with 2D as verification. The results show no difference in settlement reducing ability between triangular and square patterns. However, a triangular pattern put the geogrid under slightly more stress. The pile group on road 685 had a narrower spacing between the two outer most columns to design for a hang-up effect by the adjacent soil when it settled. Based on the simulations, where the outer distance was constant, the load distribution in a pile row and displacements in the underlying soil appeared as uneven.No field measurements were conducted on road 685 to calibrate the simulations, but the results suggest a piling pattern with equal pile spacing. Depending on the allowed settlements, with regards to the load on the pile group, there is a potential for an increase of the pile spacing up to roughly 1.5 m from the standard of 1.2 m as maximum. However, more field tests, numerical computations and laboratory models are needed to confirm the results.
Place, publisher, year, edition, pages
2016. , 124 p.
Teknik, Finita elementmetoden, PLAXIS 3D, träpålning, soft soil
IdentifiersURN: urn:nbn:se:ltu:diva-47407Local ID: 4f40d7a5-66b1-4d1a-aee2-2167714b52bdOAI: oai:DiVA.org:ltu-47407DiVA: diva2:1020729
Subject / course
Student thesis, at least 30 credits
Civil Engineering, master's level
Validerat; 20160225 (global_studentproject_submitter)2016-10-042016-10-04Bibliographically approved