Design and Construction of Tunnels: Analysis of Controlled Deformations in Rocks and Soils
ments for tackling those terrains we call “difficult”, with good prospects of success, have
always made the design and construction of underground works a risky affair, which
could not therefore be faced with the same degree of accuracy as other civil engineering
works. As a consequence they have always occupied a subordinate position with respect
to similar surface constructions and in the past they were only resorted to when the latter
seemed impractical or of little use.
However, decisive progress made in the field of geological surveys, the availability
of powerful computers for making calculations and above all the introduction of excava-
tion technologies that are effective in all types of ground have created the conditions for
a qualitative quantum leap forward. The last formidable negative
The first case occurs when the ground around the cavity withstands
the deviated stress flow around the cavity well, responding elastically
in terms of strength and deformation.
The second case occurs when the ground around the cavity is un-
able to withstand the deviated stress flow and responds anelastically,
plasticising and deforming in proportion to the volume of ground
involved in the plasticisation phenomenon. The latter, which often
causes an increase in the volume of the ground affected, propagates
radially and deviates the channelling of the stresses outwards into the
rock mass until the triaxial stress state is compatible with the strength
properties of the ground. In this situation, the arch effect is formed far
from walls of the excavation and the ground around it, which has been
disturbed, is only able to contribute to the final statics with its own
residual strength and will give rise to deformation, which is often suf-
ficient to compromise the safety of the excavation.
The third case occurs when the ground around the cavity is com-
pletely unable to withstand the deviated stress flow and responds in
the failure range producing the collapse of the cavity.
the deviated stress flow around the cavity well, responding elastically
in terms of strength and deformation.
The second case occurs when the ground around the cavity is un-
able to withstand the deviated stress flow and responds anelastically,
plasticising and deforming in proportion to the volume of ground
involved in the plasticisation phenomenon. The latter, which often
causes an increase in the volume of the ground affected, propagates
radially and deviates the channelling of the stresses outwards into the
rock mass until the triaxial stress state is compatible with the strength
properties of the ground. In this situation, the arch effect is formed far
from walls of the excavation and the ground around it, which has been
disturbed, is only able to contribute to the final statics with its own
residual strength and will give rise to deformation, which is often suf-
ficient to compromise the safety of the excavation.
The third case occurs when the ground around the cavity is com-
pletely unable to withstand the deviated stress flow and responds in
the failure range producing the collapse of the cavity.
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