Field and Laboratory Investigations to Evaluate the Coefficient of Earth Pressure at Rest - NGTS Flotten Quick Clay Test Site

Abstract

The coefficient of earth pressure at rest is a key geotechnical parameter, required in almost any investigation of material behaviour. A review of literature on the in situ and laboratory determination of K0' has been carried out. It shows that a generally accepted method for the estimation of K0' is yet to come. In addition, it demonstrates the effect of stress history and time effects on the evolution of K0'.

Extensive testing with Glötzl earth pressure cells between 5 and 10 m depth at the "Norwegian Geo-Test Sites" (NGTS) Flotten quick clay test site outside Trondheim has been carried out. It suggests that installation and evaluation of results is challenging. A dilatometer test and an oedotriaxial test have also been performed. The field vane and work criterion in oedometer approaches have been tested. Scattered data material makes a unique determination of K0' challenging, from both in situ, laboratory and correlation methods.

Additionally, a general site classification through in situ, index, oedometer and triaxial testing is presented. The testing indicates a plastic clay layer above a layer of quick clay from around 7 - 8 m depth. The clay appears to be overconsolidated, decreasing with depth. Various time effects and Quaternary geological history may explain this.