WG05 - Appendix - 04
General approach - the following provides an outline of how the anticipated conditions will be dealt with
and who will be involved in the process. Where a feature is encountered then work will cease until the
work has been assessed by an approved person
Type of
Feature
Action upon
discovery
Verification
Treatment
Conduits small
essentially
horizontal
features
Assessed by
Contractor’s
geologist who will
record, approve
treatment and
notify NRW.
Deem whether feature
is active or inactive in
terms of drainage/
habitat value and is to
be retained or closed in
discussion with
Contractors
Environmental Coordinator and Natural
Resources Wales
Where active and above finished
ground levels, incorporate to land
drainage system
Caves – large
enough for
man entry,
essentially
horizontal
Avens
(narrow
vertical)
Contractor’s
geological
supervisors will
notify NRW prior to
any recording/
treatment.
Allow a fully risk
assessed inspection
and logging by
experienced cave
surveyors under
‘controlled’
conditions’ where
necessary
Assessed by
Contractor’s
geologist who will
record, approve
treatment and
notify NRW.
Sinkholes
Assessed by
(vertical, small) Contractor’s
geologist who will
record, approve
treatment and
notify NRW.
Sinkholes
(vertical
large)
Deem whether the cave
is active in terms of
drainage/ habitat value.
Agree treatment
required with
Contractors
Environmental Coordinator and NRW
Design necessary
treatment requirements
with Contractors
Designer.
Where active and below new finished
ground levels, if possible discard
from use and close the feature if not
ensure continuity of the system
Where inactive (above or below)
close feature generally. Potentially
retain above ground if there is
habitat potential in agreement with
NRW
Protect accordingly and incorporate
to the works where possible.
Treatment will depend on where
exactly the cave presents itself
within the work areas, and what form
of cave it is for example
1.
in road formation– the creation of
a spanning slab to support the
highway will be necessary ahead
of continuing construction
2.
in a cut slope a suitable access
will have to be formed potentially
with a future access point for
inspection
Minor removal and filling to level
of surrounding ground
Deem whether or not
the aven is active in
terms of drainage and
assess effect in terms
of closure with
Contractors
Environmental Coordinator and NRW
Deem whether active in
terms of drainage/habitat
value.
1.
If within the highway
construction
1. Make area safe
2.
2.
3.
4.
Remove
surrounding
overburden
Investigate and
log sinkhole
Agree treatment
required with
Contractors
Environmental Coordinator ,
Designer and
NRW
2.
Bridging with geotextile
and continue filling
above.
1.
Remove infilling material if any,
check for cavities/fissures at
base
Close base by method approved
with NRW (rapid cementitious
optional if depth exceeds 1M
vertical, e.g. concrete filled bags
or similar).
3.
4.
5.
6.
7.
Fill remaining void with
crushed, well graded
limestone
Lay geotextile over sinkhole
onto prepared surfaces (free
of protrusions)
Continue filling above in
accordance with specification
Monitor for settlement
Include details of hole in Health
and Safety file for the works.