Structural design verifications, structural analysis of tunnels - Tunnel Engineering: Basics and Additional Services for Design and Construction - page 118

γ = 1.33; when the safety of the operational facilities of the DB network and other public
safety are not affected.
For the investigation of the structural stability of frost bodies intended to serve as assist-
ing vaults for the temporary support of the ground during construction, the safety factors
shall be specified in each individual case. The value shall be at least γ= 2.0.
Design of the lining for loading case 3
(20) The design of the final lining for loading case 3 is, unless differentiated safety con-
cepts are used, to be performed using the following safety factors:
- Concrete and reinforced concrete: γ = 1.0 and
- Steelwork: corresponding loading case HA of the DS 804.
For grouted anchors, the permissible forces are to be considered according to the assump-
tion of passive earth pressure according to DIN 4125.
Special note
(21) For the final lining, special verification should also be carried out with the following
considerations:
- Ground characteristics taking into account knowledge from former geotechnical meas-
urements,
- Increased ground pressures with 1.5 times the calculation values of the regular loading
cases, not exceeding the full overburden pressure,
- Self-weight of the lining and all normally installed building elements,
- Self weight of the permanent way and
- Point loads from overhead equipment.
The outer layer may not be considered in this verification.
The moments and forces on the section determined using these considerations shall be
used to check that the limit loading on the section according to DIN 1045 (safety factor γ
= 1.0) is not exceeded. Any verification of water impermeability that may be required for
the serviceability state is omitted for this. For this special verification, the displacements
are also to be determined and disclosed.
3.8.2 Design method for steel fibre concrete tunnel linings
General. This is a new method of structural design, which takes into consideration the
properties of the material steel fibre reinforced concrete [Volume I, Chapter 2].
Possible applications of steel fibre reinforced concrete in tunnelling. When sprayed
as steel fibre shotcrete, it can be used as the tunnel advances as temporary support to the
exposed ground. As an in-situ concrete inner lining, it can serve as a permanent construc-
tion to provide structural stability and serviceability for the entire lifetime of the tunnel. In
shield tunnelling, single-layer, waterproof linings of steel fibre concrete are already being
used and offer further potential for development.
From the point of view of construction process technology, the advantage of using steel
fibre concrete as an alternative to conventionally reinforced concrete is the saving of the