Ingår som bilaga i förf:s licentiatuppsats: "Prognos av vägars bärförmåga vid tjällossningen: användning av temperatur som nyckeltal", Luleå, 2010

Den globala tendensen är ett varmare klimat och att temperaturer nära eller strax över 0 °C under vinterhalvåret blir allt vanligare. En av klimatförändringens konsekvenser skulle i ett "värsta-fall-scenario" kunna bli tjällossning under en betydande del av vintern, med följande bärförmågeproblem på vägarna. Detta leder till ökade samhällsekonomiska kostnader då tung trafik tvingas lasta mindre eller ändra rutt (tidsförlust) och ökade underhållskostnader för sönderkörda vägar. Skogsindustrin beräknades 2008 ha merkostnader på 510-590 miljoner kronor per år på grund av bärförmågeproblem enligt egna beräkningar. Till denna summa tillkommer merkostnader för den snabbt ökande biobränsleindustrin. Genom att kunna prognostisera bärförmågeproblem vid tjällossningen skulle lastrestriktioner läggas i rätt tid och väghållar- och användarkostnader minskas. Ett enkelt mätetal kopplat till bärförmågan kan användas för att prognostisera när och hur länge vägen har bärförmågeproblem, alltså när lastrestriktioner bör appliceras för att vara mest kostnadseffektivt. En fullt fungerande prognosmodell skulle också kunna minska behovet av fallviktsmätningar och okulära besiktningar vid införandet av lastrestriktioner. Denna forskningsrapport är en del i ett arbete som behandlar prognostisering av bärförmågeproblem på vägar. Rapporten syftar till att ge en bild av om en temperaturbaserad bärförmågeprognosmodell, "Minnesotamodellen", kan uppfylla detta mål genom att jämföra prognosmodellens resultat med bärförmågeanalyser utförda med hjälp av fallviktsmätningar. Datainsamling i form av temperaturdata och fallviktsdata utfördes 1997 på Björsbyvägen cirka 7km utanför Luleå centrum. Den aktuella vägprofilen för vägsträckan där data hämtats består av 10cm oljegrus, 40cm sandigt grus/grusig lerig sand och 300cm siltig lera underlagrad av siltig morän. Fallviktsmätningar och utvärdering av bärförmågeindex, ytmodul, undergrundsmodul och AREA-parameter finns beskrivna. Ytmodul och undergrundsmodul visar styvheten på olika djup i vägkonstruktionen, AREA-parametern ska med ett tal sammanfatta hela vägkonstruktionen och bärförmågeindex är ett index som beskriver styvheten hos vägen. Hur temperaturinsamlingen är genomförd finns även kort beskrivet. Alternativ länk: http://pure.ltu.se/portal/files/5167873/Prognos_av_v_gars_b_rf_rm_ga_vid_tj_llossningen___Anv_ndning_av__Minnesotamodellen__p__en_teststr_cka_i_Sverige.pdf

The global trend towards a warmer climate and temperatures near or just above 0 °C during winter months, will most likely be more common in future. One of the consequences of this climate change could, in a worst-case scenario, be freezing and thawing over a significant part of the winter with corresponding road bearing capacity problems. Bearing capacity problems may lead to increased costs to society when heavy traffic is forced to change route or carry less weight. In addition, road maintenance costs will increase. According to pulp industry calculations, this industry sector will face additional costs in the range of 510-590 Million SEK every year due to road bearing capacity problems. In addition to this, the costs related to the rapidly growing bio fuel industry will be added. If a reliable forecast of load-bearing capacity problems and potential load restrictions on roads can be found, it would be cost effective for road administration and society. This research report is a part of a work to find methods to forecast bearing capacity problems on roads. The report gives an idea of the possibility to use the temperature based model used in Minnesota, USA in Sweden. The evaluation is done by comparing falling weight deflectometer (FWD) test results with the results from the temperature based forecast model. Temperatures and FWD data were collected in 1997 on a road approximately 7 km outside Luleå, Sweden. The road structure was from the surface: 0,10 m asphalt, 0,40 m sandy gravel/gravely clayey sand and 3,0 m silty clay overlaying a silty moraine. In the report the FWD concept, as well as the FWD parameters of importance are described. How the temperature data was collected is described. The temperatures were collected at a depth of 0,20 m and 0,12 m below the asphalt layer respectively. FWD data was normalised to a force of 50kN. The radius of the segmented falling plate was 0,12 m and all calculations were carried out in accordance with Swedish guidelines. Based upon the FWD tests, the following parameters were evaluated: i/load carrying index, ii/surface modulus, iii/subgrade modulus and iv/“AREA-parameter”. A daily average air temperature was determined based upon the detailed measured temperatures. A comparison was done with an average value calculated solely on the recorded maximum and minimum temperatures. It is shown that the two methods gave similar results when used in the forecast model. A short description of the temperature based forecast model is presented as well as an example of how to use it. The needed reference temperature was in the field test evaluated to - 0,65 °C and the thaw-degree day limit before the road starts to thaw was determined to 22,2 °C-days. The evaluated FWD parameters show bearing capacity loss at slightly different days. Load carrying index shows a loss of bearing capacity after March 14. As expected the surface modulus is strongly influenced by the air temperature and shows low values on March 10, April 1. After April 11 it decreases significantly. The subgrade modulus shows less stiffness after March 26 and is not as affected by changing air temperatures as the surface modulus. The AREA parameter is also affected by the oscillations in air temperature, much like the surface modulus. It shows low values on March 10 and April 1. After April 11 it decreases significantly towards the lowest values registered in the study. The temperature based forecast model shows that the limit for the accumulated thaw index is reached on March 10 and on April 22-23. The results from the forecast model based upon the daily average temperatures and based upon daily maximum and minimum temperatures only, shows almost the same dates for bearing capacity reductions. Thus, the more simple method with maximum and minimum temperature values seems to give enough accuracy. When comparing the FWD results: AREA-parameter and subgrade modulus with results from the Minnesota model, the subgrade modulus seems to have the greatest agreement with the forecast model. However, they both seem to show the overall development of low bearing capacity during thaw. The overall conclusion about the temperature based forecast model is that it seems to give fairly good results and work well. It will work better if it can be further calibrated but it has some flaws if the temperature seesaws around 0 °C. The forecast model should, despite this, be able to assist road holders in Sweden as a planning tool, when dealing with bearing capacity problems during thaw.