On Prevention of Crackings Over the Road Surface Below which Snow Melting System Utilizing Geothermal Water is Buried

Abstract

Since 1966 a geothermal-snow-melting-system for roads has been operated at Jozankei Spa, Sapporo, Japan, to cover 1, 628 m (11, 880m²) as of May of 1982. The snow melting system consists of polybuthene pipes embedded in pavement. The inlet and outlet temperatures of geothermal water which is forced by pumps to circulatethrough the piping system are about 80°C and 30°C, respectively. A couple of years ago, shallow and narrow crackings were found over several parts of the road surface below which polybuthene pipes were buried. Although the polybuthene pipes of relatively low heat-resistivity were embedded in low temperature aggregates or the dense grade asphalt concrete, enfeeblement of the pipes are expected. Also, for advancing the heating effect on road surface the depth ofthose pipes were shallowed to 5cm. To avoid the danger of destruction the embedded pipes under those conditions, conventional macadam rollers (10 to 12 ton) and tirerollers (8 to 15 ton) were not used but 5-ton-vibrating rollers. Then the cause of cracking may be considered lack of compaction. Some laboratory experiments were carried out to determine the preferable structure of pavement and to examine strength of pavement for vehicles travelling in order to prevent occurrence of the crackings.