Tunnelling risk - Practical Engineering Geology - page 400

Appendix E-2 Example of hazard and risk prediction table
Example table of predicted hazards at option/design stage for TBM with potential intersection of old mine workings, karst, collapsed and weak zones; this is
part of a more detailed report prepared for a speci

c project and was supported by similar tables for drill and blast options, detailed text, recommended methods
of working, international case studies and discussion.

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

H1. G I 1 boreholes and packer tests
2. pre-construction geological desk
study and risk assessmen t*
3. surface grouting ahead of tunnel
4. probe drilling ahead of and around
the face through TBM 2 head.
Monitoring of water volume and
pressur e*
5. inspection of probe drill cuttings for
weak or unconsolidated material,
monitoring of strata colour and
odour for unanticipated changes *
6. TS P 3 to detect likely geological
structure s*
7. monitoring of water make from face
and signicant changes in volume or
pressur e*
8. ground probing radar to detect
cavities, clay or high density of
fractures
9. geological mapping to detect changes
in structure, strata distress

1 Inrush of water

or unconsolidated
ground

cavity, fault,
area of
collapsed
ground, shaft,
adit

L H H 1. failure to identify inrush

conditions
2. blockage of probe holes
with debris, or
unconsolidated material
resulting in
underestimation of water
pressure and volume
3. failure of grouting
programme
4. failure of EPBM 4
bulkhead
5. injury to workforce
6. partial or complete loss of
tunnel drive

1. GI = Ground investigation
2. TBM = Tunnel boring machine
3. TSP = Tunnel Seismic Proling or Prediction
4. EPBM = Earth pressure balance tunnelling machine

continued overleaf