Project Details
Projekt
Improvement of organic soils using unencased sand columns - Optimisation of measurement, simulation and prediction of long-term settlements in test fields
Applicant
Professor Dr.-Ing. Frank Rackwitz
Subject Area
Geotechnics, Hydraulic Engineering
Term
since 2025
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 575619680
As Germany's infrastructure network expands, it is often inevitable that transport routes will pass through peatlands or coastal regions with organic soils. Due to their special properties (viscosity, fibrousness, anisotropy), these peats and muds exhibit a pronounced time-dependent deformation behaviour. Secondary settlement due to soil creep can have a significant impact on the long-term stability of traffic embankments. To improve the bearing capacity and deformation behaviour of such subsoils, columns can be used as an alternative to soil replacement or deep foundations. Sand columns are particularly environmentally friendly and economical due to their installation and the absence of binders and geosynthetics. In Germany, unencased sand columns are rarely used due to the lack of design guidelines and the assumption that sand columns will retain their shape and fail due to insufficient radial support in soft subsoil. The overall aim of this knowledge transfer project is therefore to promote the use of unencased sand columns in practice by solving these problems. The previous DFG project 'Verbesserung der Tragfähigkeit organischer Böden mittels Sandsäulen' (No. 262373812) has already demonstrated the dimensional stability and durability of the columns on a model scale. Based on this project, four work packages have been developed in order to transfer the results of the basic research into practice. The core of the planned project is the implementation of full-scale in-situ tests in an extensively instrumented test field in cooperation between the applicant's working group and the application partner EUROVIA. In four full-scale tests, the long-term bearing and deformation behaviour of an embankment fill on organic soil improved with sand columns will be investigated by varying the column spacing. The use of fiber-optic sensors will be tested to assess the dimensional stability and deformation of the columns. The field tests will be complemented by a laboratory programme to determine the soil properties and by extensive numerical investigations. A numerical parameter study will be used for a more detailed investigation of the effects of column installation and creep, as well as the influence of the anisotropy of the organic soil. Finally, the results of these work packages and the basic research will be used to develop a practical approach for predicting the long-term settlement of the improved soil. Creep deformation as well as soil-specific and installation-related influences will be taken into account to enable safe and economic design. The results of the project will be incorporated into various working groups with the aim of including uncoated sand columns in German design guidelines for ground improvement measures.
DFG Programme
Research Grants (Transfer Project)
