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SUMMARY
In the boundaries of this thesis, the subject that was put under discussion
was the mechanical behaviour of energy piles. Their construction and use is a
rare occurance in our days, which actually renders them as a relatively new field
in the profession of Civil Engineering. However, the economic and environmental
profit that they have proven they can offer, only throughout those few aplications,
seems quite tempting for the future.
The main issues that were examined over this subject consist firstly of the
mechanical behaviour of individual energy piles, either under axial or lateral
loading and then of the mechanical behaviour of an axially loaded group of
energy piles in the scenario of the energy function of the whole group as well as
the scenario of the energy function only of the central pile in the 3x3 group.
During the research of the issues above, many various results emerged about the
influence of the thermal loading to the mechanical behaviour, something that all in
all signifies their special studying, a requirement for their final use.
Namely, in the aspect of the axially loaded individual piles, it was proven that
the final value of the bearing capacity doesn’t develop any major differences, but
on the contrary, as the results indicate, there are significant changes in the axial
tension, due to the thermal loadings of the pile. Specifically, after the enforcement
of the cooling stage, there is a strange phenomenon presented of a gradually
changing effect, where, from the initial reduction of the compressive axial tension
at low values of the axial load, gradually the behaviour of the pile is converted into
the increase of the compressive axial tension, due to the cooling phase, as the
value of the axial load increases. Furthermore, examining the results of the
heating of the individual pile, there appears to be an increase of the compressive
axial tension, regardless of the axial load.
Moving onto the aspect of the laterally loaded individual piles, differences
owing to the thermal loading are observed again only in the distribution of the
axial tension, as the diagrams of the lateral load – horizontal displacement,
vertical force and bending moments don’t present any substantial change.
Finally, as for the subject of the examining of the two different energy
functions of the piles group, it was observed that at the case of the energy
function of the whole group, there is generally a tendency towards the increase of
the compressive axial tension, regardless of the case of the thermal loading.
However, in the case of the thermal loading of only one pile in the group, an
intense reduction of the compressive axial tension was emerged as a result of the
cooling phase and on the other hand, at the end of the heating phase of the pile,
appeared the exact opposite mechanical behaviour. As for the rest of the piles in
the group, the differences that were noted in the distribution of their axial tension
were of inferior size and importance.
5. iv
The results mentioned above, can be attributed to a a series of factors, like
the thermal contracions and expansions of the piles and the foundation ground
around them, the model of state of the simulation of the interface between pile
and ground, as well as the static boundary conditions (like the free heads of the
individual piles or the headband connecting the piles in the case of the group).
Concluding, from all the analyses that were carried out, a very complex
phenomenon is reflected, which, as mentioned before, represents a quite new
field in the branch of Civil Engineering and demands a more thorough research
for the establishment of correct and representative theoretical models that can
describe accurately the nature of the phenomenon and will help tremendously in
the evolution of this technology.