Case Study: Road Embankment Foundation on Weak Organic Soils

The paper presents the problem of embankment foundation during reconstruction and extension of regional road 110 on the section Witomierz - Grądy. On this section the road crosses the valley of meltwater formed during the last Weichselian glaciation. It is a watershed area between the streams Stuchowska Struga and Otoczka Reska. In the Holocene a 961 ha fen peat called Wielki Smogorze has been formed. There are favorable conditions in the area for the formation of fen peats. The thickness of the peats is over 4 m, reaching almost 8.0 m in its peak. Since 1964 the Przybiernówko-Grądy II deposit (402 ha) is continuously exploited. Currently, the deposit is being used by a company called "Lasland". Extraction is conducted on the basis of a relevant concession within a designated mining area of 242.9 ha. The mining concession is valid until the end of 2030. The pits are deep and are located on both sides of the regional road no. 110. Peat is transported by narrow-gauge railroad to the nearby processing plant, where it is sieved, sorted and packed. Based on the analysis of available archival materials, the road as found today was functioning already in the middle of the 19th century. In the 1970s the road was widened to 6.0m In 2003 due to the bad condition of the surface the asphalt layer was renovated by applying a grid and new asphalt layers. During the renovation longitudinal cracks have been reported and there were problems with the compaction of the mix. The direct cause was the shallow layer of peat located just 1.1 - 1.3 m under the road. Conducted renovation did not bring expected results, so in 2019 the documentation for the reconstruction of the road was prepared. Different methods of road foundation were analyzed, from soil replacement through the use of piles. In the end the decision was made to directly settle the embankment with the use of geosynthetics. This study presents a selected solution and shows the results of calculations. Changes during the execution of the reconstruction were discussed. The applied solution allowed for simultaneous functioning of the mining plant and reconstruction of the regional road on the section of 1.2 km. geotextiles and geonets were used. The main argument for such solution was relatively low cost of reconstruction and time of execution. During construction there were problems with obtaining the parameters on the substructure for asphalt layers. Two alternative solutions were proposed, one of which required increasing the thickness of embankment reinforced with geo-mesh and an additional layer of CBGM mix substructure. The solution allowed to meet the design requirements and complete the reconstruction according to the plan without any problems.