On the impact of temperature perturbations on the creep of sensitive clay
A systematic series of temperature-controlled laboratory tests (5 to 25 ◦C), including oedometer tests with static and cyclic thermal loading steps, has been carried out on natural and remoulded samples of natural sensitive clay from the Utby test-site in Gothenburg, Sweden. An original time-saving test protocol is developed to obtain sufficient data within the duration of the project. The results demonstrate that the influence of the temperature on the creep rate of sensitive clays depends on the amount of natural bonding. Heating increments lead to larger changes in creep rate than cooling decrements. The thermal loading cycles lead to larger permanent strains when compared to the static heating and cooling paths.
Thorough analyses of the results using the temperature-invariant rate-dependent model implemented in a multi-physics numerical framework indicates that the temperature dependency can be uniquely linked to the amount of natural bonding in the clay sample. Consequently, the temperature-invariant model is modified by correlating the apparent preconsolidation pressure with temperature and the amount of natural bonding in the clay samples. The temperature-dependent model, Creep-SCLAY1ST, improves the predictions of the mechanical response under static thermal loading considerably, whilst the modelling of the cyclic loading paths proved to be somewhat unsatisfactory. The latter is not a shortcoming of the proposed model modification, rather an intrinsic limitation of the underlying temperature-invariant model.
apparent preconsolidation pressure
static thermal loading
Chalmers, Arkitektur och samhällsbyggnadsteknik, Geologi och geoteknik
Interestingly, the places in the world that would benefit most from geothermal energy, i.e. the Nordic countries and North America, also have large areas with soft sensitive clays that can be easily disturbed and sometimes change from solid ground to a liquid. Therefore, we study the sensitive clay from Gothenburg in the laboratory to find out how it reacts to temperature change and how it behaves under different temperatures. We use the results to better understand the process, and to create a computer model that helps us to safely design facilities embedded in sensitive clays that exploit geothermal energy.
The story is not yet finished, although based on this work we now can capture and predict the effects of temperature in the sensitive clays, we still do not know why the clay reacts to the temperature changes. That would be another enjoyable research.
Building Futures (2010-2018)
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4568
Chalmers tekniska högskola
SB-H4, Sven Hultins gata 6, Göteborg
Opponent: Prof. Jean-Michel Pereira, Laboratoire Navier, École des Ponts ParisTech Paris, France