Uppföljning av tjälåtgärder på lågtrafikerat vägnät i Norrbotten: Jämförande studie mellan dimensionering och utfall
Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
Seasonally frozen ground is a common condition in northern parts of the world and especially low traffic roads are extensively exposed to large amounts of frost damage every year. Problems occur when the construction of the roads are affected by uneven frost heaves during wintertime or during spring under the thawing process. PMS Object is a calculation program which the Swedish Transport Administration, Trafikverket, provides for road construction. The program contains a model for calculation of frost depth and the expected frost heave within a specified road embankment. The calculations require input data as given material properties of the soil, layer thicknesses and climate data. The results however, based on past experience, has in some cases been discovered to not correspond to reality. The subsequent consequences might be that wrong measures for reparation and/or improvement of the roads are carried out. The purpose of this thesis is to study how the calculated results from PMS Object corresponds to reality and try to distinguish certain situations in which the problems of misleading results arise. The results from this study are intended to serve as a prelude to future updates of the frost calculation model which is a part of PMS Object. Five road objects located in Norrbotten were selected for the study. The main part of the study was accomplished through practical work consisting of frost damage inventorying, collection of data from archived construction documents and also by performing frost heaving calculations using PMS Object. Later on, the calculation results and outcomes from the inventory and data collection are bound together and compared against each other. The thesis also includes a brief literature study regarding frost, road construction and frost impact on roads. The inventory shows a varied impact degree regarding frost damage between the different objects of study. However, all but one of the selected objects was affected by frost damage at many of the recently improved road sections. The necessary excavation depths which first are calculated using PMS Object compares to the excavation depths which were performed during the latest improvements according to existing construction documents. The necessary excavation depth is calculated with a criterion of a maximum allowable frost heave of 100 mm, this assessment corresponds to a reasonable measure against frost based on experience from Trafikverket. For three out of five possible objects included in the study, the results showed that the excavation depth surpassed the required theoretical depth calculated by PMS Object, yet several of the excavated areas had acquired frost damage. The object most affected was damaged in 13 out of 25 excavated areas which clearly show that improvement measures have either been inadequate or incorrect. Many uncertainties and difficulties which occurred during interpretation of the results are discussed in the report. This is for example inventory uncertainties, difficulties regarding soil classifications etc. Regarding the calculation model included in PMS Object there are especially two significant factors identified with great impact on the out coming results: the maximum lifting rate of the terrace material and also the choice of weather station which the climate data is retrieved from. In the report it is shown that small changes of these factors leads to great differences in the results and furthermore it clearly points out the difficulties concerning the decision of which weather station is the best one to use. The study as a whole shows that the excavation depths calculated with PMS Object in many cases are insufficient and that there exists a need to update the model for frost calculations. Alternatively one course of action might be to review the criteria for maximum allowable frost heave. In the study it was not possible to identify any particular situation in which the problems of recurrent frost damages were more prevalent.
Place, publisher, year, edition, pages
2013. , 138 p.
IdentifiersURN: urn:nbn:se:ltu:diva-44202Local ID: 1ffa5950-8151-4c1a-9bd2-03b0bda28aedOAI: oai:DiVA.org:ltu-44202DiVA: diva2:1017478
Subject / course
Student thesis, at least 30 credits
Civil Engineering, master's level
Validerat; 20130819 (global_studentproject_submitter)2016-10-042016-10-04Bibliographically approved