THERMAL PROTECTION ON FINNISH ROADS

Thermal insulations are generally used in transition areas at the border of frost-susceptible and frost-resistant soil or rock. The results of research and economic investigations indicate that expanded polystyrene is the most expedient of all materials and that extruded polystyrene (more costly than expanded polystyrene) insulated slabs are the most reliable from point of view of water absorption. It is recommended that on roads sections with no significant risk of slipperiness, the insulation may be placed at a depth of 50 cm. A design nomogram for polystyrene insulations is presented by which the required thickness of insulation can be determined by taking into consideration, the degree of cold and other conditions of the construction project. The length of the wedge-formed insulation built at the border of frost-susceptible and frost-resistant soil or rock is of essential importance. A nomogram is illustrated from which this length may be obtained on the basis of the level of service of the road and the measured or estimated frost heave. Normal transition wedges and earth box structures are discussed in some detail. Investigations indicate that the bottom gradient of wedges built for levelling off frost heaves should be about 1:2-1:30, depending upon the geographical location of the project, in order that road surface damages could be eliminated or reduced. The wedges of high class roads should be designed so that there will not be variations, settlement or frost-heave larger than 3 percent. The depth of the wedge is (at least) 1.6 m, 1.8 m and 2.0 m in South, Central and North Finland respectively. Impermeable frost-resistant aggregate (sand) is used as fill for earth boxes in order that the best possible "heat store" is formed in this moist course to prevent frost penetration.