Improvement of the load-deformation behavior of organic soils by means of sand compaction piles

• Applicants: Professor Dr.-Ing. Frank Rackwitz; Professor Dr.-Ing. Stavros A. Savidis
• Subject Area: Geotechnics, Hydraulic Engineering
• Term: from 2015 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 262373812

The aim of this research project is to investigate the load deformation behaviour of organic soils improved with uncased sand columns. Data available on the efficiency of organic soil improvement using compacted, uncased sand columns are currently very limited, especially on the influence of different installation methods of the sand columns. Creep, which occurs in particular in organic soils, is a time dependent process and develops over a long period of time. This behaviour has not yet been investigated and is therefore not part of any design model. The time dependent stress development after the installation of the displacement sand columns has also not been the topic of any previous investigations. Furthermore, the possibility of differential settlements between the organic soil and the sand column has also not yet satisfactorily been investigated. Based on the knowledge gained from 1g model testing as well as numerical analyses, different design approaches for these sand columns constructed by displacing the organic soil during their installation shall be developed. Testing in the laboratory will be divided into two parts. In one part the interaction between the subsoil and the sand columns will be analysed und evaluated. The behaviour of organic soils will be analysed in another part of the laboratory testing. The emphasis of these tests is to investigate the dependence of the load concentration to the cross-sectional area of the sand columns according to their spacing and their installation method. The main aim of the 1g model tests is to determine the influence of two different installation methods, namely the installation of the compacted sand columns by displacement or replacement of the organic soil. These tests on different scales shall than be compared against each other and also be used to make a judgement of the dimensions needed for a large scale prototype sand columns. The results from soil mechanical element tests are needed to gain a fundamental understanding of the soil mechanical behaviour of organic soils and to define the input parameters for the finite element analysis. These element tests shall include compression tests with restricted side deformation as well as consolidated, undrained triaxial tests. In order to investigate the behaviour of anisotropic, organic soils, a Rowe cell will be used which has to be purchased in the frame of this research project. Using this equipment, the load-deformation behaviour for different drainage and loading conditions can be accurately measured. Combining the results from all the laboratory tests, a prognosis for the deformation behaviour of prototype sand columns will be possible according to their installation method and cross-sectional area. A validation of this forecast will then be possible using the pre-defined finite element model.

• DFG Programme: Research Grants