Tierakenteen rasittuminen yli 76 tonnin HCT-yhdistelmien koekuormituksissa vuonna 2018

This report presents the results of studies conducted in 2018 concerning strain on the road structure by heavy goods vehicles. It follows on from the report on studies conducted between 2015 and 2017. Special focus was on cumulative deformations caused by the load imposed by consecutive axles and the potential pumping effect forcing water into the road structure on roads built on soft soil. The measuring sites for the study were selected on the basis of the sites used for the studies in the years 2015 to 2017. Deformations at these sites were observed with displacement sensors installed on the lower surface of the pavement and rut depths measured with the laser scanner of an RDSV vehicle. A laser distance meter was used to monitor how well the vehicles used for the load test kept to the track specified on the road. No changes in moisture were detected with the measuring methods used at the test sites on load testing days in 2018.
At two paved test sites, the purpose was after the melting of the ground frost in spring 2018 to perform a test on two consecutive days to compare the response from one 7-axle vehicle of about 64 tonnes passing over the measuring point to the response from two 7-axle vehicles of about 64 tonne each passing over the measuring point one after the other, when the total mass passing over the measuring point over a given length of time was the same. Also, the aim was to reduce the rut created or to prevent the rut from deepening by controlled varying of the track taken by the test vehicles. At the Kyyjärvi test site, the load impact of a special bogie installed on a trailer on the road structure was also tested on one day. In autumn 2018, reference tests were conducted at one paved site and one gravel road site. The reference tests were conducted over two days: one articulated vehicle was driven in the first morning and another articulated vehicle in the first afternoon; on the next day, their order was reversed.
At the test site in Simo (road 924), with a thin pavement on sandy soil, the road structure withstood the loads well in the tests in spring 2018, and rut formation was slight, as heavy vehicle traffic had compacted the road. There was no measurable difference in rut depth caused by the passing of one 7-axle vehicle and two consecutive 7-axle vehicles. At the Kyyjärvi test site (road 16863) in spring 2018, where the pavement had the weakest structure among the test sites, with a pavement thickness of only about 30 mm, the deformations were far more pronounced than in Karstula or Simo. However, the initial conditions at the test site in Kyyjärvi after the melting of ground frost were not consistent from day to day because of imperfect road compacting, and a reliable comparison between the vehicles could not be made.
The load tests conducted in Kyyjärvi on two consecutive days in autumn 2018, on a road on soft soil, demonstrated that a 14-axle articulated vehicle increased rut depth but a single 7-axle articulated vehicle if anything reduced rut depth, or rut depth remained unchanged, when the load mass over a given length of time was the same in both cases. At the gravel road test site in Ranua in autumn 2018, the situation was the same: a 14-axle articulated vehicle caused a greater increase in rut depth than a single 7-axle articulated vehicle.
At the test sites in Kyyjärvi and Simo in spring 2018, controlled varying of the track taken by the test vehicles clearly reduced rut formation. Indeed, a few passes of the test vehicles in this manner caused the rut depth increase caused earlier in the day to almost return to the level prior to the test.