Cyclic Response of Natural Onsøy Clay

In geotechnical applications cyclic loading occurs frequently caused by earthquake shaking, traffic or wind and wave loading. The consideration of cyclic loading effects finds increasing attention nowadays. This particularly holds true for structures, which are of civil importance and involve high investment costs. Sophisticated calculation approaches are applied within the design process of these boundary value problems. However, many of the calculation models assume undrained stress paths, where cyclic loading leads to a continuous generation of excess pore water pressure. When soft, marine clays under slower loading are involved, the dissipation of excess pore water pressure becomes relevant. The transient consolidation process needs to be considered. Thus, in the present paper the consolidation behaviour of Norwegian Onsøy clay as a typical representative of natural, marine clay under cyclic loading is analysed. Part I of this paper presents the experimental study. Testing results from monotonic and cyclic oedometer tests on natural as well as remoulded clay are introduced. The differences in the compression behaviour and pore water pressure dissipation of structured and remoulded clay are illuminated. Furthermore, the effect of cyclic loading characteristics, as e.g. the load amplitude, on consolidation is analysed. Part II of the paper comprises a numerical study. Modelling the cyclic consolidation processes by use of FEM, the focus of the analysis is set on the necessity of different features of a hierarchical model to analyse this type of boundary value problems.