Tunnelling risk - Practical Engineering Geology - page 402

(continued)

Hazard Possible mitigation measures prior to

and during construction to reduce
likelihood or consequence of hazard

Impact of
mitigation
measures and
risk

Summary of main
residual risks

Title Example of

circumstances

Notes * indicates technique more likely
than others to be useful

10. provision of adequate ventilation
(and if necessary methane drainage
system )*
11. adoption of

ammable gas working
practices (no smoking policy, safety
light policies, intrinsically safe plant
and equipment
12. consider also likelihood of hazards:
1, 3, 4, 5, 7, 8, 9, 10, 11, 12 and 17

3 Noxious gases (eg

CO2, S02, H2S

as 1 above M 1. GI boreholes

2. pre-construction geological desk
study and risk assessment *
3. geological mapping of face cuttings
to detect changes in structure and
strata, presence of organic material,
sulphides, etc *
4. monitoring of tunnel atmosphere
(gas monitoring at top and base of
face) to detect signi

L L L 1. failure to identify gases

2. injury to workforce
3. temporary evacuation of
drive during remedial
works

cant changes in
character or composition *
5. probe drilling ahead of and around
the face through TBM head.
Monitoring of character of ush

return
6. provision of adequate ventilation *
7. consider also presence of hazard 2

continued overleaf