Geology Reference
In-Depth Information
(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
7. monitoring relative volume of spoil
produced and driveage distance to
identify caving ground
8. use of strata control (eg bentonite)
foams ahead of face
9. grouting ahead of face
10. grouting behind liner to
ll cavities
11. consider also hazard 1, 2, 8, 9, 10,
11, 12, 13, 14, 15, 16, 17
8
Cavity << tunnel
diameter
karst, old
mine
workings,
possibly
faults
M
1. GI boreholes
2. pre-construction geological desk
study and risk assessment
3. probe drilling ahead of and around
face through TBM head.
Monitoring of rates of drilling and
character of drill cuttings (presence
of clay, in
L
L
L
1. failure of grouting
progmeram
2. difculty in maintaining
tunnel alignment
3. higher risk of water or
gas inrush (see above)
ll materials etc)
*
4. TSP to detect air or water
lled
cavity (unlikely to detect small
cavities)
5. geological mapping to identify
disturbed or fractured structure and
strata distress
6. consider also hazard 1, 2, 9, 10, 11,
12, 13, 14, 15, 16, 17
continued overleaf
