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
* i
ndicates technique more likely
than others to be useful
9
Cavity ~ tunnel
diameter
karst, old
partial
extraction
mine
workings
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 to detect cavity
2. failure of grouting
programme
3. dif
culty in maintaining
tunnel alignment
4. higher risk of water or
gas inrush (see above)
ll
materials etc
)*
4. TSP to detect cavity
5. geological mapping to identify
disturbed or fractured structure and
strata distress
6. grouting ahead of face to ll cavities
to create plug to improve driving
conditions and help minimise TBM
deviatio
n*
7. grouting behind lining to
