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Träpålnings inverkan på den odränerade skjuvhållfastheten i sulfidhaltig kohesionsjord: En fallstudie på väg 685 Vibbyn - Skogså, Bodens kommun
2014 (Swedish)Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

Sulphide soils are in general, from a geotechnical perspective, considered as a problematic soil because settlements easily can occur and these soils have a relative low shear strength. These soils are also a problem from an environmental perspective as they oxidate when they come in contact with oxygen, creating acidifying products. The sulphide soils have unfavourable geotechnical properties which might cause problems during road and railway constructions founded on these loose sediments.The Kippelbäck bridge along road 685 between Vibbyn and Skogså in Boden municipality have suffered from large settlements and yearly flooding as a consequence of this. Since the last repara-tion of the bridge and the road in 1992, over 2 meters of settlements have occurred. The settle-ments where caused by a defective construction of the bridge and the connecting road. The Swe-dish Transport Administration together with BDX as contractors have during 2013-2014 restored the road. In the most critical areas the road has been reinforced with wooden piles to reduce the settlements.The purpose with this study has been to investigate if wooden piles have any effect on the un-drained shear strength in loose sulphide soils. The Swedish Transport Administration has during the construction of Haparandabanan investigated the undrained shear strength before and after piling using vane shear tests. The result showed an increased strength on all investigated levels. The goal with this thesis has been to find if a change of strength exists after that the wooden piles have been installed and determine which methods that are most suitable for such an investigation.A literature study has been performed to get an increased understanding about sulphide soil and its properties as well as wooden piles and their impact on the surrounding soil. From a strength perspective, it is worth mentioning that today the same empirical model is used for normal clay and sulphide soil, which can give misguiding results.Field investigations have been performed at four different occasions during autumn 2013 and in January 2014. The first investigations were performed before the pile driving was started and the three remaining where performed after the pile driving had been completed with an interval about 1-1.5 months. The used field methods were piston sampler, CPT and pore pressure measurements. The performed laboratory tests were direct shear tests and routine investigations where especially the undrained shear strength has been studied through fall-cone tests.A conclusion that can be drawn from this work is that in-situ methods are to prefer in situations where the shear strength is to be evaluated. The reason for this is that the stress conditions that occur due to the piling and the overlying construction can be hard to recreate in laboratory, in for example undrained shear strength tests. Perhaps it is possible to find the correct stress paths with simulations by using finite element methods. The performed cone penetration tests (CPT) showed almost a 300% increase of the undrained shear strength for the deepest levels. It would have been interesting to perform vane shear tests in order to compare with the results from the CPT.

Place, publisher, year, edition, pages
2014. , 82 p.
Keyword [en]
Keyword [sv]
Teknik, sulfidjord, träpålning, odränerad skjuvhållfasthet
URN: urn:nbn:se:ltu:diva-59134Local ID: fa8bfd6a-5ddd-4079-ac0e-75ff7ee8aad4OAI: diva2:1032522
External cooperation
Subject / course
Student thesis, at least 30 credits
Educational program
Civil Engineering, master's level
Validerat; 20141222 (global_studentproject_submitter)Available from: 2016-10-04 Created: 2016-10-04Bibliographically approved

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