4.1 Mechanical and Electrical
• Breakdown
• Hydraulic oils
”A plan whatever it may be must be made for the bad ground, it must be calculated to
meet all exigencies, all disasters and to overcome them after they have occurred”
(Remark by M I Brunel on the occasion of proposals for improvement after the
flooding of the Thames Tunnel 1831)
In mechanised tunnelling requirements as to safe working conditions can be more
easily fulfilled than in conventional tunnelling. The obligation to consider economic
and quality assurance aspects has been realised for years.
General safety requirements
In the design of the tunnel-boring machine, the following measures for achieving
safety shall be taken into consideration:
• Specification of hazards and assessment of risks
• Elimination of hazards or limitation of risks
• Provision of safeguards against identified hazards which cannot be totally
eliminated
• Training level for machine operators
Materials
Materials used in the manufacture or operation of the machinery shall be chosen so
as to reduce the danger to exposed persons health and safety and shall not create
toxic fumes in case of fire.
Contact surfaces
Accessible parts of a machine shall be designed an manufactured to avoid an
exposed persons contact with sharp edges, angles or rough surfaces which are likely
to cause injury. The same applies for hot surfaces.
Protection against ruptured hoses and pipes
Hoses and pipes which may become ruptured and thereby cause damage to persons
should, where feasible, be firmly secured and protected against external damage and
stresses. Adequate shielding to protect persons and machinery shall be provided in
working areas.
Cutter Head on Tunnel Boring Machines (TBM)
If it is necessary to gain access through a bulkhead to the area behind cutter
head/shield and similarly through a cutter head to the area in front, the manhole
openings of adequate size shall be provided.
The design shall allow for safe access for inspection, service and maintenance work.
Face support such as slot gate closures and/or compressed air may be provided.
The cutter head shall be equipped with a device to prevent unintentional movement
of the head. This device shall be actuated if the cutter head is stopped for other
reasons than those normal to its working operation.
Handling of heavy loads
Where the weight, size or shape of parts of a machine prevents them from being
moved manually the parts shall be either fitted with attachments for lifting gear or
designed so that they can be fitted with such attachments or be shaped in such a
way that standard lifting gear can easily be attached.
When the ground support system requires the lifting of heavy units an erecting device
shall be fitted. In all cases, winches and drive motors shall be fitted with mechanical
brakes, which are powered off during operation.
Loss of stability
All shield machines act as temporary ground support during the tunnelling
operations. The shall therefore be designed to withstand the loads imposed by the
surrounding ground together with any dynamic loads imposed by the action of driving
the machine forward.
All information pertinent to the structural design of the shield shall either be
appended to the maintenance manual or be available from the manufacturer
throughout the machine lifetime or at least for 10 years, whichever is the shorter.
When grippers are fitted to a full face TBM and are in use it shall not be possible to
start the cutter head drive or apply the thrust force until the minimum required
gripping pressure has been reached. Should the gripping pressure fall below this
minimum the cutter head rotation shall be stopped and the thrust force shut off
automatically.
All shields may be subject to slow rotation due to imbalance of loads. Care should be
taken in the design and manufacture of the shield machine and back-up equipment to
avoid exocentric loadings and all machines shall be fitted with an effective counter
rotation system such as an angled plough, for returning the machine and back-up
equipment to the correct orientation. Sudden rotation of a shield machine may occur
when a cutter head or boom becomes embedded in the face. All such machines shall
therefore be fitted with a protective device, which cuts off power to the drive motor in
the event of the shield machine rotating in a rapid manner.
There is always a danger of face collapse in open face tunnels in soft ground. All
shield machines where open face excavation can take place shall be provided with
mechanical face support systems appropriate to the ground conditions envisaged.
These supports may include hydraulically operated poling plates and face plates,
sand trays etc.
There is a serious risk of physical injury or drowning to persons working on a shield
machine should the tunnel or shaft be flooded. All shield machines shall be designed
to accommodate pumping equipment adequate for