On the impact of temperature perturbations on the creep of sensitive clay
Doctoral thesis, 2019
Temperature affects the soil response, but is not fully understood and quantified and thus often ignored. The temperature fluctuations resulting from energy foundations and construction activities, such as excavations and soil stabilization, however, may lead to changes in the hydromechanical response of the clay. Especially, the sensitive clays that are abundant in Scandinavia, may be detrimentally affected. The fragile natural bonds between the clay platelets of sensitive clays are prone to disturbances from environmental changes, including temperature perturbations. The change in hydro-mechanical properties, such as the compressibility and the creep-rate, can affect the long-term stability of the geothermal structures. The aim of the Thesis is to study 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.
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.
thermal cycles
sensitive clays
oedometer tests
temperature
natural bonding
apparent preconsolidation pressure
multi-physics modelling
geothermal
static thermal loading
SB-H4, Sven Hultins gata 6, Göteborg
Opponent: Prof. Jean-Michel Pereira, Laboratoire Navier, École des Ponts ParisTech Paris, France
Author
Yanling Li
Chalmers, Architecture and Civil Engineering, Geology and Geotechnics
How do people feel under different temperature and react to temperature changes? As sensible human beings, we dress and act accordingly. The question investigated in this Thesis is how the soil will react to temperature change and behave under different temperatures. This is particularly important when we are using the energy stored in the ground during summer to heat buildings in the winter. This is called shallow geothermal energy, a sustainable energy resource which is becoming more and more popular.
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.
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.
Areas of Advance
Building Futures (2010-2018)
Energy
Materials Science
Subject Categories
Energy Engineering
Other Materials Engineering
Climate Research
ISBN
978-91-7905-101-3
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4568
Publisher
Chalmers
SB-H4, Sven Hultins gata 6, Göteborg
Opponent: Prof. Jean-Michel Pereira, Laboratoire Navier, École des Ponts ParisTech Paris, France