INTRO | HIGHLIGHTS | FEATURES | INTERVIEWS | PERSPECTIVES
Managing
environmental
risks from
Britain’s
mining legacy
Steven Kershaw
explains the risks
left by coal mining
in Britain and
how they can be
managed
A ‘crown hole’ which opened by the side of a highway.
A shaft that was used for pumping water in order to
control water levels in the mines.
CENTURIES OF MINING IN BRITAIN
has left a legacy of abandoned
underground mines that continues to
represent a risk to public safety and
environmental contamination that will
exist for many centuries to come. The
Coal Authority, founded in 1994 to look
after the legacy of the coal industry,
owns the estate of coal seams and mines
within Britain. In 2014 it will celebrate
its 20th anniversary of addressing these
risks on behalf of the nation. Its principal
roles are the control and treatment
of mine waters, treating the effects
of subsidence and providing mining
information to the public, as well as
licensing the mining of coal.
RISKS TO THE PUBLIC
A principal risk to the public is the
ground collapsing above abandoned
mine workings. A thousand such
incidents per year are reported to the
Coal Authority, approximately half of
which are mining related. There is a
24/7 hazard line where the public can
phone in to report mining hazards and
there are regional staff who can respond
as soon as possible after notification.
The collapses are largely associated with
old shallow workings at depths of less
than 30 metres below the surface and
mine entries, especially shafts, where
collapses occur into voids.
These failures can cause damage
ranging from something that might
represent a trip hazard to something
that might swallow buildings or people.
Most typically, the damage arising from
shallow workings manifests itself as a
crown hole, where the collapse of the
mine roof into a void migrates upwards
until it reaches the surface. After filling
any voids, shafts are typically fitted with
a reinforced concrete cap to prevent any
further collapses.
The geographical scale of the areas
potentially at risk is large. Abandoned
coal mine workings in Britain cover
thousands of square kilometres with a
significant percentage of these being at
shallow depth. The shallowest workings
tend to be those that were mined first
and are therefore usually the oldest.
43
But abandonment plans have only
had to be legally submitted to the HM
Inspectorate of Mines since 1872, so
there are many old workings, abandoned
before that date, where no documentary
evidence exists.
INSPECTING MINE RISKS
There are 170,000 recorded mine
entries within the coalfields. There is
probably a similar number of shafts
which were never recorded or archived
and whose positions remain unknown.
These mined areas are often close
to urban centres which grew on the
coalfields during the industrial revolution
and afterwards. Records show that there
are over 58,000 recorded mineshafts
in urban areas. This close relationship
between potential mining hazards and
the areas where people live creates
particular problems for public safety.
The large scale of the problem and
the fact that collapses are very hard to
predict, means that expensive proactive
remediation of shallow mine workings
and shafts is not carried out unless
there is a clearly identified reason to do
so. Typically, remediation will occur if
developers wish to build over land that
might have instabilities. This will usually
involve filling workings with grout (fly
ash, cement, and water) and building
concrete caps over the shafts.
Known shafts represent discrete points
where failure could occur and therefore
represent a clear identifiable risk to
the public. In 2008 the Coal Authority
began a programme of inspecting all the
locations of recorded shafts, in order to
identify whether there were any particular
risks that needed to be addressed. At
present 85,000 mineshafts have been
visited and between 1