Abstract:
In this study, the ground improvement method that applied to the approach embankment of a bridge within the scope of the Ankara - Sivas Railway Project in Sivas, Turkey was investigated as a case study. The bridge is located between Km:358+200- Km:359+100. Earth concrete wall constructions in the approach fillings were completed as of September 2017. 90 cm of weak ground excavation was made, and no additional ground improvement was applied during the construction stage. Some deformations of the reinforced earth concrete walls and extra settlements in the embankment were observed. The approach embankments of up to 13 m height are over clay, conglomerate, pebbly sandstone, and mudstone units. Due to the vertical stresses transferred to the saturated cohesive units, the pore water pressure of the soil increases, and due to the low permeability of the soil, settlements occur for a long time. Therefore, the consolidation settlement amounts and settlement times are calculated on the basis of the data obtained from the one-dimensional consolidation test for the study area. As a result of the calculations, it was seen that engineering measures were necessary for the approach embankments.
It is a challenge to apply a ground improvement method with a railway under service and a tight timeline. Hence, a feasible ground improvement technique with the advantages such as the variety of soil conditions that the technique can be applied, application speed, and the application's depth must be chosen. Considering these problems of the project, a ground improvement method that limits the settlement of the ground while improving the strength of the ground the deep soil mixing (DSM) method was selected. In order to bring the consolidation settlements to permissible limits, improvement with inclined deep mixing applications was proposed, taking into account the thickness of the compressible clay layer and applicability. As a result of the analytical calculations, it was determined that the settlement and stability problems are prevented with the inclined DSM application for the embankments. The DSM columns were designed with a diameter of 60 cm, 3 to 4 rows in cross-section, 1.5 m vertically, 1 m apart horizontally, and with various lengths, according to the soil conditions. To achieve the best results in the rail embankments, the application of inclined DSM columns is designed to be 45 degrees with horizontal.
Finally, in the study area, the DSM columns application was completed successfully as of November 2021. The strength of DSM columns was confirmed through the core samples were taken from the DSM columns and the compressive strength tests were performed in the laboratory. In addition, the deformations sourced from the settlement are prevented. This study presents the challenges in predicting the settlements of the embankments and the analytical calculations to assess the performance of ground treatment by DSM columns. Moreover, this study is important as it shows that the DSM columns can be successfully applied as inclined structures within a railway under service.