Analysis of ULSD theory – Spread foundations

The article continues to a discussion the theory of ultimate limit state design (ULSD) and its consequences. An influence of definitions both characteristic and design values of soil parameters of EN 1997-1 (Code) is pursued. The paper has two basic theoretical aims: a) to examine the reliability of ULSD in geotechnics for spread foundation design and due to it an extent both of its in-effectivity and risk, b) to test a concept of a more plausible and correct design theory which is simpler and in compliance with mathematical principles applying it for spread foundation design. The new concept was tested formerly for a case of slope design (Koudelka, 2018). Spread foundation designs based on the design approaches of the Code are compared with another approach on direct definition of design values based. The foundation analysis exploits the results of a statistical analysis of an extensive database of soil properties. The analysis is based on data sets of sandy and fine-grained soils and aims at the risk of homogeneity for ULS designs. Another simple geotechnical design concept suitable also for advanced numerical methods is compared.