No abstract

No abstract

No abstract

After an introductory presentation of design approaches the risks involved are investigated. Considered are different ground improvement methods, like soil mixing, vibro compaction and vibro stone columns, as well as pile-like supporting elements, including vibro concrete columns and full displacement columns named rigid inclusions. The difference in stiffness of the inserted material and the soil determines the design and the risks involved. Three categories with increasing risk are proposed. Ground improvement methods, ductile in compliance with EN 1997-1 and DIN 1054, proved to be extraordinary robust and present only a small risk with regard to a possible variation of soil and material parameters and loads. The design is usually determined by the serviceability limit state. Risks increase with the application of non-ductile methods with small column diameter, like rigid inclusions, because the ultimate limit state is controlling the behaviour. Namely, in order to mobilize high skin friction, the lower and upper end of the column have to fail during punching in the soil below and the load transfer platform above. Even a small variation in material parameters, system geometry or loads may lead to a complete loss of bearing capacity and progressive failure, resulting in expensive damages of civil engineering structures and time consuming repair works.

The characteristics of different subsoil layers and groundwater conditions are the most significant factors when estimating the response of the ground under changing stress conditions. The interaction between the ground properties of the various homogeneous areas determine the portfolio of geotechnical solutions for achieving technical project requirements. Consequently the determination of realistic parameters has a decisive influence on the selection of potential geotechnical methods both during design and execution. This opportunity for achieving an optimal design and construction method can quickly become a risk to everyone when the soil at the site has not been investigated adequately, and subsequently structural damages occur together with all the related consequences. Using a case study from real construction projects, it will be shown how site investigations can lead to additional opportunities to meet the project goals for everyone involved in the construction task.