FINNISH FIELD TESTS ON SOIL-STRUCTURE INTERACTION OF INTEGRAL ABUTMENT BRIDGES

Traditionally long bridges have been built with bearings and expansion joints. In order to avoid them the jointless practice has been adopted. Jointless or integral abutment bridges have their superstructure cast integrally with their substructure. In the Finnish research program on road bridges the main subjects of interest were: possible problems with jointless bridges; earth pressures; construction details and the behaviour of pavement near the abutments. The instrumentation of Haavistonjoki Bridge at Tampere-Jyvaskyla highway is presented. The bridge is a 56 m long continuous 3-span slab bridge, unskewed and totally jointless. The instrumentation was completed in autumn 2003. The data were collected by monitoring during 2003 to 2008 altogether 191 gauges installed in the bridge structures during construction period. The instrumentation was used to measure, for instance, the abutment's horizontal displacement, abutment rotation, abutment pile strains, earth pressure behind abutments, pier strains, superstructure displacements, frost depth, air temperature as well as thermal gradients in the superstructure next to abutment piles and in the approach embankment. The results show for example that the vertical strains inside the piles follow the horizontal abutment displacements. The measured earth pressures on the bridge abutments were quite high because the backfill was well compacted and the values calculated with a soil modulus of elasticity E(d) = 250,000 kPa corresponded best to the measured values. The research program was extended to railway bridges and mostly to the track-bridge interaction and the behaviour of the integral railway bridge abutment with or without transition slabs. The field test program on a railway bridge is also presented.