Civil Engineering Reference
In-Depth Information
Geology and hydrology.
In order to produce an alternative proposal for mechanised tun-
nelling, binding statements about the type and extent of the obstructions in the ground are
necessary. The geotechnical data have to be evaluated regarding the overcoming of fault
zones.
The soil mechanics properties for the estimation of potential sticking and the wear pa-
rameters for excavation tools and mechanical parts (seals) also have to be determined and
evaluated.
In addition, the suitability of the ground for grouting and conditioning should also be
assessed. In particular, the environmental acceptability of the materials used has to be
decided.
From the information available about the geotechnical conditions, the suitability of the
excavated soil for tipping or recycling and for separation also needs to be assessed.
Finally, when a tunnel boring machine with grippers is to be used, the capability of the
rock to resist bracing forces also has to be estimated.
Design and construction process.
The design concept has to be optimised for mecha-
nised tunnelling with regard to the layout of niches, breakdown bays and cross-passages.
The number of niches has to be restricted to the necessary minimum, the tunnel cross-
section enlarged to integrate escape routes (excepting niches, breakdown bays) and the
segment concept adapted to suit the necessary emergency measures.
The performance of additional measures, delivery and assembly times, segment produc-
tion and logistics are all requirements, which have an effect on construction operations.
Further aspects of importance for the planning of construction operations are the launch-
ing and reception processes, the construction of niches and connecting tunnels, the analy-
sis of interruptions and risk, fire and explosion protection and a geotechnical measurement
programme.
The specification for mechanised tunnelling should include specific additional points
concerning advance probing, advance dewatering, advance ground drainage, overcom-
ing obstructions, checking excavation quantities, recording operational data and shield
control with safety equipment, and the visualisation of geological faults. Any rebuilding
or conversion of the tunnelling machine or alteration of material conveyance to another
operating mode should also be included in the specification.
The design should take into account requirements affecting the lining such as fire/explo-
sion protection, waterproofing and impact loads. Requirements resulting from geometrical
criteria (curve radius, tolerances), influences resulting from the advance of the shield and
grouting openings also have to be considered in the design of the lining.
Tendering and contract.
The tendering of a tunnel project for mechanised tunnelling
should include the determination of geological risk. It is the task of clients to describe the
ground conditions in detail and produce geotechnical forecasts. Contractors are responsi-
ble for technically correct dealing with the ground and should also perform their own site
investigations.
The contract should also regulate the implementation of additional measures, which could
become necessary to overcome fault zones or for passing under buildings susceptible to
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