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
12
Metal
obstructions
old mine
workings,
surface GI
boreholes
(lost drill
strings) and
lost bits from
advance
drilling
H
1. pre-construction geological desk
study and risk assessment (presence
of old mine workings)
2. maintenance of good GI drilling
records and records of advanced
drilling programm
e*
3. monitoring of face production rate
s*
4. stop machine draw back and use
cutting or explosives to remove
obstacle
s*
5. Consider also likelihood of 1,
particularly 2, 7, 8, 9, 10, 11, 13, 14,
15, 16, 17
M
H
H
1. failure to identify
possibility of metal in
face
2. stability problems and
damage to cutter head
3. unable to cut or remove
metal from ahead of
TBM due to face
instability or water make
4. delays to programme
5. dif
culty in maintaining
tunnel alignment
13
Subsidence along
tunnel line
karst and
old mine
workings
beneath
tunnel line
H
1. GI boreholes, identi
cation of karst
L
H
H
1. failure to identify
unconsolidated ground
2. failure of grouting
programme
3. workings/karst too deep
to consolidate from
tunnel
4. settlement of TBM,
delays to programme and
loss of line
5. failure of tunnel lining
post construction
or mineworkings
2. pre-construction geological desk
study and risk assessmen
t*
3. probe drilling ahead of face and
beneath tunnel to detect areas of
weak ground. Monitoring rates of
drilling and character of drill
cutting
s*
4. identi
cation of karstic or mining
feature
s*
continued overleaf
