Structural design verifications, structural analysis of tunnels - Tunnel Engineering: Basics and Additional Services for Design and Construction - page 96

hydration process influences the development of ground pressure and deformation. The
quality requirements for the construction materials, like for example concrete strength, are
often negatively influenced by local conditions.
Collaboration of the contract parties. Employers, consultants, contractors, appointed
specialists and supervisors must have not only professional qualifications but also expe-
rience and the will to achieve technical and economic success. (The number of parties
involved should be as few as possible). Measurements and calculations serve as criteria
for structural stability and for further proceeding. The trade skills of the men on site have
a decisive influence on the loosening of the rock mass, avoidance of rock falls and the
quality of support materials.
These special features may seem negative but are balanced by positive features:
- The reserves of load-bearing capacity in the rock mass as a composite with the support
materials are high, as long as the rock mass is dealt with expertly.
- The possibility of evaluating measurements made on site and comparing them to design
calculations provides evaluation criteria for structural stability.
- If the construction process is adapted in good time with additional strengthening, this
helps to avoid large deformation or even collapses.
The variety and range of variability of the special features mentioned in comparison to
normal structural engineering make tunnel construction one of the most interesting but
also challenging engineering disciplines. In no other field do theory and practice have such
an effect on each other and have to be overcome with knowledge of structural analysis,
materials technology, geology, machine technology and particularly construction process
technology. Each of the parties involved in the project, whether site manager, consultant,
appointed specialist or supervisory engineer needs basic knowledge of these varied disci-
plines. The site manager cannot interpret measurements and introduce immediate meas-
ures to adapt the process without knowledge of the structural design and geology; and
the consultant cannot produce a meaningful design without knowledge of construction
process and procedures on site.
Requirements. The verification of structural stability has to include analysis and calcula-
tion of the play of forces between rock mass and support at various stages, taking into ac-
count the construction process and excavation methods. Verifications of structural stability
are normally performed as part of dimensioning the elements. The special features already
mentioned do not permit this to be done unambiguously, so construction processes and
constructional solutions have to be investigated and critical phases identified. In addition,
building regulations, at least in Germany, require verifications of structural stability to be
performed, and the procedure to be adopted also has to be justified with calculations to
professional colleagues, certainly after the occurrence of a collapse or failure.
In order to avoid repeating material from the extensive literature, which reaches back
into the 19 th century, the most important terms and models connected with the verifica-
tion of structural stability will now be summarised and arranged according to their ap-
plication. Examples from tunnels built in recent years are intended to document current
practice.