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
8. geological mapping to anticipate
permeable or fractured structure,
strata distress etc
9. grouting ahead of face
*
10. advanced dewatering ahead of
tunnel from the surface
11. ground freezing ahead of face
12. consider also hazard 1
6
Excessive
groundwater
pressure
as 5 above
M
1. hydrological testing in GI boreholes
2. pre-construction geological desk
study and risk assessment, tunnel
dept
h*
3. probe drilling ahead of face through
control valve grouted into rock
ahead of TBM cutters and
monitoring of water volume and
pressur
e*
4. monitoring of water make from face
and signi
M
H
H
1. failure of grouting
programme ground
freezing
2. underestimation of
groundwater pressure
3. failure of EPBM
bulkhead
4. failure of pumps
5. temporary evacuation of
drive or
6. temporary or permanent
loss of drive
cant changes in volume or
pressur
e*
5. TSP to detect likely geological
structures
6. ground probing radar to detect
cavities, clay or high density of
fractures
continued overleaf
