Kuivatusratkaisujen toimivuuden ja vaikutusten arviointi

The previous “Cost efficiency of drainage improvements on existing railway tracks” report from 2018 stated how the water content has a significant impact on the performance of track substructure materials. In this report, the research has been continued by finding out the real in-situ conditions on track with the help of three measurement stations. The sub-ballast samples were collected from field sites and load tested in the laboratory. The load bearing capacity of the sub-ballast materials was examined by static and cyclic triaxial tests. The effect of water content to load bearing capacity was significant in both testing methods. In static tests with four different materials, the shear strength increased, when the soil saturation degree (SR) was less than 40–50 %. In cyclic tests, the best load bearing capacity was always achieved with the driest samples, typically about 35–60 % saturation degree. The saturated samples were clearly most vulnerable to large deformation in cyclic test. Based on field measurements, the water content of sub-ballast varies significantly from site to site and from depth to depth. The critical (>70 % SR) water levels occur mainly below ground water table and on springtime, when the frost and snow are thawing, in the upper part of sub-ballast layer. The role of capillarity water was small and extends only slightly above the groundwater level. Transition measurements could not detect a clear relationship between the moisture in the structure and the resulting displacements, although there were small indications of it in some places. The in-situ substructure evaluation was also developed in this research project by testing Panda2 dynamic cone penetrometer. Based on an extensive series of laboratory and field tests, the water content influences the dynamic cone resistance measured by the device, but the significance of the soil density is clearly higher. Because of that, good and poor-quality substructure materials cannot be characterized by using their dynamic cone resistance. In conclusion, the Panda2 device was found to be better suited for compaction control during construction. With poor quality substructure materials, the stability of the track geometry is likely to be weakened, if the water content of materials is close to the saturated state and the traffic load is heavy. Especially the quality and saturation degree of the upper part of sub-ballast material are important. Some materials in Rantarata (km137) are susceptible to the effect of water content but usually the load bearing capacity of materials are not fully utilized because there is no heavy axle load (250kN) traffic on Rantarata. Improvements of track drainage should be aimed at targets, where the ground water table is close to the top of the sub- ballast layer. Flooding should also be avoided even in exceptional situations.