The local influence of a house on the inner slope stability

The local influence of a house on the inner slope stability

van der Zee, N.

Jonkman, S.N. (mentor)
de Gijt, J.G. (mentor)
Terwel, K.C. (mentor)
Kool, J.J. (mentor)
van der Sman, R. (mentor)

Civil Engineering and Geosciences

Hydraulic Engineering

2017-02-12

In the Netherlands almost 17.500 kilometers of primary flood defenses protect the flood prone areas from inundation. These flood defenses are designed and periodically assessed according to certain design standards which require an average probability of exceedance of 1/1.250 or 1/10.000 per year. From the results of recent assessments, it was found that a lot of dike sections could not be assessed due to the presence of Non-Water retaining Objects (NWOs), such as buildings Non-Water retaining objects are structures which are not part of a flood defense, such as buildings. The current methods only consider a 2D cross sectional profile to assess the safety against an instability. In case a building is present in the dike, this is neglected by assuming it to be absent. This limitation led to the subject for this research thesis was formed: “What is the local influence of a building on the reliability of the inner slope stability of a dike section?” Current developments with computational models provide an opportunity to implement a dike section containing a building in the 3D Finite Element Method. Based on the amount of time such a computation takes and the limitations of the model choices, first some analytical calculations were performed. The important sensitivities which were found were the dimensions of the building, the position of the building (both depth and distance from crest), the weight of the building, the stiffness of the walls and the tensile strength of the masonry building. From both the analytical calculations the following overall conclusions were found. - The increase in soil pressure against the building from the dike will be limited during the initiation of an instability - The stability of the dike is not influenced by the stiffness of a building, although deformations for the different stiffness’s are different - The pressure on the soil retaining wall does show different values, however it does not show an increase during instability w.r.t. the normative conditions. For a building with common dimensions and loads which can be used to schematize a building it has been found that a local instability will almost never occur. In case extreme loads or unfavorable positions of a building over a larger length are present, the local instability can occur (think of high rise buildings on top of the crest for example). - A local instability will be compensated by the more stable boundary effects It can be questioned whether the increased 3D stability will result in an attraction of larger loads towards the building. In case the building would be subjected to higher loads (from the soil), the structural safety could become critical. In case the building collapses, a different type of sliding plane will occur. This can endanger the overall dike stability. In case a building remains intact during extreme conditions, it can be stated that the influence of an (intact) building on the stability should be considered. In such scenarios the assumption of a hole in the dike at the location where the building is situated is a conservative image of the actual stability. It is noted that this thesis is very deterministic. Uncertainties in soil and structural properties have only been considered by performing some sensitivity analyses. It is therefore suggested to analyze the uncertainty in the soil and building in a more detailed or probabilistic research. Current models such as the heterogeneous dike profile analyses using the Random FEM could be looked into. Such models may also give a more realistic view on the local influences such as uneven deformations and local soil disturbances.

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Student theses

master thesis

(c) 2017 van der Zee, N.