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
10
Cavity >> tunnel
diameter
karst, old
partial
extraction
mine
workings
H
1. GI boreholes
2. pre-construction geological desk
study and risk assessment
3. probe drilling ahead of and around
through TBM head. Monitoring of
rates of drilling and character of drill
cuttings (presence of clay, in
L
H
H
1. failure to detect cavity
systems
2. failure of grouting
programme
3. unable to drain cavities
4. signi
cant delay to
programme
5. signicantly increased
risk if water and gas
inrush and settlement
(hazards 1, 2, 3 and 16)
ll
materials, etc)
*
4. TSP to detect cavity
5. geological mapping to identify
disturbed, fractured or distressed
strata
6. grout cavities ahead of tunnel face
(may be very dif
cult
)*
7. drain cavity, take TBM off line and
construct dummy tunnel rings on
tunnel line, grout remaining cavities
around lining then advance through
dummy tunnel. Note: this option
may not be possible due to water
make
*
8. consider also hazard 2, 3, 4, 8, 9, 10,
11, 12, 14, 15, 17 and particularly
hazards 1 and 16 during construction
continued overleaf
