Final Activity Report Summary - CULVERTS (Large-span flexible corrugated steel culverts) Full-scale field tests of two large-span flexible steel culverts were the main project objective. The first culvert is a horizontal ellipse located at Dovre and the second structure is a pipe-arch culvert located at Tolpinrud, both locations in Norway. The researcher carried out measurements on both structures.Various gages were used for long-term monitoring of different parameters during live loads for the structures at Dovre and Tolpinrud. These were:* Glötzl hydraulic earth pressure cells to measure stress changes in the soil around the structure,* laser gauges to measure the horizontal deformations of the structures.Tests were taken to assess structure and soil behaviour as well as culvert-soil interaction during long-term service. The measurements on the Dovre and Tolpinrud structures proved that the arching effect above the structures is quite stable and is still working after 21 years of service. The CULVERT project identified the magnitude of the arching effect in long-term service of flexible structures. The maximum horizontal deformation measured on the Dovre ellipse during the 21 years of observation was 22 mm and the maximal horizontal deformation during construction was 35 mm. It means that the difference of deformation between construction phase and the service period is about 13 mm during 21 years of observation.In addition, the load reduction (arching effect) on deep buried rigid structures using EPS geofoam was tested and analysed during the fellowship. Long-term full scale tests of buried rigid culverts with EPS geofoam showed that there is no marked increase in vertical earth pressure after the end of construction. Based on the full scale tests and finite element analyses, it is recommended to use a width of the expanded polystyrene that is 1.5 times the outer diameter of the pipe. The vertical earth pressure in the section with expanded polystyrene was reduced to less than 50 % of the overburden. These are the most important and significant scientific achievements.Moreover the response computed using the two commercial codes based on the Finite Element Method were compared and verified by the experimental data obtained from tests and the results from test of the box culvert were analysed during the fellowship.The obtained test results from both the Dovre and Tolpinrud structures as well as the box culvert soil-steel bridge and rigid culverts with EPS provide a wealth of data on the type of objects investigated in the study. The data give an insight into actual behaviour of such structures under long-term service conditions.The test results from long-term field measurements of multi-plate flexible corrugated structures and buried rigid culverts in Norway as well as finite element analyses have been presented on six international conferences.