Calculating long-term settlement in soft clays - with special focus on the Gothenburg region
Licentiate thesis, 2010
Long-term settlement in clay constitutes an engineering challenge in road design and construction in areas with deep deposits of soft clay. Soil improvement and construction of building foundations or embankments can be quite complicated and expensive in such areas. Construction costs need to be balanced against high maintenance costs. In order to do this optimally, there is a need to predict long-term settlement with a high degree of accuracy.
Two different test sites were chosen for back-calculation, a test embankment at Nödinge and a groundwater lowering at Kaserntorget. There was also one hypothetical test site.
In this thesis a short description is presented of the fundamental behaviour of soft clays with regard to compressibility as well as a short explanation of the theory for the three different models that has been used within this thesis – Embankco, GS Settlement and the Soft Soil Creep model.
Soil parameter determination for long-term settlement analysis is discussed together with some of the inherent complications. For the IL oedometer test the study shows that if the time for the load stage of interest is not sufficiently long the evaluated creep parameter could be misleading. Back-calculation of CRS oedometer tests, using the Soft Soil Creep model, is performed for this model and a procedure is suggested.
The outcome of the analysis shows that all three models produce similar results for the hypothetical case. For the two test sites in question, both GS Settlement and the Soft Soil Creep model were capable of predicting the measured settlement with acceptable accuracy. The Embankco program was only used for the hypothetical case.
Keywords: Soft clay, creep, test sites, long-term settlement.