Comparative settlement analysis by using 3D-GIS and 2D-FEM approaches

2000. Comparative settlement analysis by using 3D-GIS and 2D-FEM approaches / by N.B. Yenigul, Delft : ITC, 2000. - 117 p. ; 30 cm. - ITC MSc-thesis. ABSTRACT, supervisor(s): Ozmutlu & Zigterman, thesis availability: ITC Library

ABSTRACT

The surcharge due to buildings and roads affects subsurface and ground behavior and causes settlement problems. Since resulting damage and repair work may cost considerable amount, an accurate modeling of subsurface conditions and prediction of ground-structure interaction can help avoiding such undesirable foundations. In this research, settlement analysis by using three-dimensional geographic information system (3D GIS) and two dimensional finite element (2D FEM) modeling are both carried out and the results are compared and correlated.

Settlement analysis by using 3D GIS approach is performed for two different geometrical conditions by using modified Terzaghi or so-called Koppejan Formula for long-term settlements. The compressibility coefficient involved in the formula has been determined considering three different approaches and the analysis is performed for each of them. Thereafter the settlement results are presented as settlement prediction maps for comparison purposes and as 3D iso-volumes to reflect the real picture of settlement predictions.

After performing the 2D based settlement analysis on the sections taken from the 3D-geology model, the results are compared and correlated visually and statistically with 3D analysis results at the same sections. Statistical analysis results showed that there is a significant linear relationship and a very strong correlation between 2D FEM based and 3D GIS based settlement analysis results. The order of magnitude difference between 2D FEM based and 3D GIS based results is mostly due to constitutive laws of the software and the parameters and equations used in calculations. Terzaghi equation, which is used in 3D settlement calculations, is a logarithmic function whereas the 2D analysis is based on a linear function according to Hooke's Law of linear elastic stress-strain relationship. Five different soil units, which have different E values and CM values determined on the basis of different approaches, thickness of layers considered in two approaches, volume weighted average method used in 3D settlement analysis are the other factors that play a role in the difference in the order of magnitude of settlement results. The number of variables affecting the results restrained the comparison between the results of 2D and 3D settlement analysis to be qualitative rather than quantitative.