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R. Lackner:
"Thermochemomechanics of cement-based materials: from material modeling to applications in structural design";
TU Wien, Vienna, Austria, 2002.

This thesis comprises seven publications (Publication A to Publication G) covering recent developments in the solution of multi-field problems with emphasis on cement-based materials. In contrast to single-field problems, which are characterized by the determination of one field of unknowns such as, e.g., the displacement field or the temperature field, multi-field problems allow to account for the interaction (couplings) between different field variables. In the description of cement-based materials, such interactions are commonly observed, such as, e.g.,

(a) the increase of the hydration speed, i.e., the speed of the chemical reaction between cement and water, in consequence of higher temperature (thermochemical couplings);

(b) the increase of strength and stiffness of cement-based materials in consequence of the progress of the hydration process (chemomechanical couplings).

In order to describe the different (relevant) couplings in cement-based materials, a thermochemomechanical material model
was developed at Vienna University of Technology. The theoretical
framework and the algorithmic realization of this material model are outlined in this thesis. The material model is applied to three problems taken from civil engineering:


(1) Monitoring of cracking in RCC dams

The development of roller-compacted-concrete (RCC) dams started approximately three decades ago. Structural engineers (involved with concrete-dam design) together with geotechnical engineers (traditionally involved with embankment-dam design) were trying to
combine the best features of both major types of dams. The so-obtained RCC dam exhibits the safety and maintenance advantages of concrete dams and the low cost and high production rates of earth or rockfill embankments. Nevertheless, the large dimensions of RCC dams caused a significant increase of the temperature in the course of the hydration process. The deformations related to the temperature
increase (thermomechanical couplings) resulted in the opening of cracks at the free surfaces of the dam. The undesirable consequence of cracking in a dam is leakage which occasionally causes internal erosion. The developed thermochemomechanical material model was employed for the assessment of the cracking risk in RCC dams. Insight regarding the adaptation of the construction process in order to avoid cracking is gained. The determination of the material functions for the simulation of early-age cracking of RCC and the application
of the material model to an RCC dam are contained in "Publication A".


(2) Quantification of stress states in shotcrete tunnel shells

The New Austrian Tunneling Method (NATM) has proved to be a very economic and flexible mode of construction. When driving tunnels according to this method, after the excavation of a cross section of a tunnel, shotcrete is applied onto the tunnel walls, constituting a thin and flexible shell. Recently, hybrid methods were developed,
allowing determination of stress states in shotcrete shells. Hereby, the term "hybrid" refers to the combination of the developed thermochemomechanical material model with in situ displacement measurements of the shotcrete shell. "Publication B" contains the application of the hybrid method to the closed tunnel shell of the Sieberg tunnel (Austria). Moreover, the algorithmic framework of the developed material model is outlined in this publication. The extension of the material model to consideration of early-age cracking of reinforced concrete is given in "Publication C". The hybrid analysis of the Sieberg tunnel, already reported in Publication B, is repeated. This time, however, a new hybrid method characterized by an increased efficiency and robustness is employed.
In both publications, Publication B and Publication C, the assumption of isothermal conditions allowed to reduce the analysis to a chemomechanical analysis accounting only for chemomechanical couplings in shotcrete. Departure from isothermal conditions, i.e., consideration of thermochemical couplings, is described in
"Publication D". The thermochemical analysis and the subsequent
chemomechanical analysis are performed for the Lainzer tunnel (Austria). In both tunnels treated so far, i.e., the Sieberg tunnel and the Lainzer tunnel, a closed shotcrete shell was installed. In squeezing rock conditions, however, excessive deformations may cause
strains which a closed shotcrete tunnel shell cannot sustain. To prevent the shell from damage, longitudinal gaps may be left in the shell. A hybrid method for the analysis of such segmented shotcrete shells is contained in "Publication E". It is employed for the determination of the stress state in the segmented shotcrete shell
of the Semmering pilot tunnel (Austria).


(3) Assessment of jet-grouting support in tunneling

Among many methods for ground improvement, jet grouting is characterized by the widest range of applicability to different types of soil. The high flexibility of this method has resulted in many applications in civil engineering, such as underpinning, the installation of sealing slabs, and applications in tunneling.
"Publication F" is concerned with the material properties of soil
improved by means of jet grouting. A new method for determination of the cement content in jet-grouted soil mass is proposed. It is based on the combination of the developed material model for cement-based
materials and in situ temperature measurements at the center of jet-grouted columns. Via back analysis, both the cement content and
the radius of jet-grouted columns can be computed. The cement content of jet-grouted soil mass strongly influences the strength and the stiffness and, hence, the load-carrying capacity of jet-grouted
columns. "Publication G" deals with the application of jet grouting in tunneling. During the excavation of a tunnel, jet-grouted columns are installed horizontally from the tunnel face, finally forming a canopy of improved soil. The effect of this canopy on the surface
settlements of shallow tunnels is investigated for the underground
station Taborstrasse (Vienna, Austria).