12th International Symposium on District Heating and Cooling

the street the more shallow the shaft is [3]. On theother hand if too little coverage over the pipe is chosen,it may get hit by a rock curb or a supporting leg from atruck with no cover.The <strong>12th</strong> <strong>International</strong> <strong>Symposium</strong> on District Heating and Cooling,September 5 th to September 7 th , 2010, Tallinn, EstoniaFig. 4 Marking of the location of the gauges.Fig. 2 Left; Supporting leg with no cover, Right; Rockcurb.If the existing fraction is used as backfill transports canbe reduced which lower the costs and theenvironmental influence.Normally the district heating pipes have no problemscoping with the traffic load. The extra pressure and themovement in the soil are making extra loads that arequite negligible compared to the thermal load, the innerpressure load and the load from the outer pressurefrom the soil.To get an idea of if the graphite gaskets used in thepipe joints (for casaflex) can stand the traffic load200 mm below the surface in a street with heavy trafficthe traffic load was empirically measured in the testarea.The test shaftThree displacement gauges were placed in a test pipecontaining air (see section 2.1) beside two operatingpipes (see Fig. 3–5). Two accelerometers were placedin separate boxes near the test pipe. The gauges weremonitored through wires at the bicycle path beside thestreet.The test was done with two single district heating pipes162/76,1 (DN 65) casaflex buried in a fraction withgrain size 0–40 mm. (Normal standard is a fraction ofsand 0.2–16 mm.) The distance from the top of thepipes to the top of the fraction was 60 mm. (Normalstandard is 460 mm.) The distance from the top of thepipes to the top of the asphalt was 200 mm. (Normalstandard is 600 mm.)As extra protection, the operating pipes were wrappedin a grid of polyethylene, PE.EXPERIMENTALThe tests were done during 2009–2010.The test siteAn industrial street classified as a street with2000–4000 passes of vehicles for every lane and dayas an average through the year was chosen as the testsite. The extension of the test area was 8 meters as thepipes crossed a street.The gauges were placed in one of the lanes close tothe centre of the street. The location of the gaugeswere visualised with a cross on the asphalt (see Fig. 4).Fig. 5 Shaft section in the test area including the test pipe.Before laying the asphalt, the fraction was compressedwith a 500 kg plate compactor.The pipes are designed for 1.6 MPa but the localhydraulic pressure is approximately 1.4 MPa. Thedesigned temperature for the district heating water is110 °C. The real temperature varies between 70 and100 °C in the supply pipe and between 40 and 60 °C inthe return pipe.Fig. 3 Drawing over the test area.97About casaflexThe type of pipe, casaflex, was chosen to overcomethe thermal loads and the working conditions (i.e. the