27
d
&
ri
MARCH-APRIL 2014
EXPLOSIVE
DEMOLITION
Night lights
Tower block specialist
Safedem was recognised
for a contract it successfully
carried out in the Scottish
city of Greenock.
D&Ri
reports
A
s part of a Regeneration Area project
within an area of the Scottish city
of Greenock in Inverclyde, which
forms part of an estate of mixed mature social
housing, client River Clyde Homes (RCH)
identified an area for redevelopment through
the demolition of blighted housing stock that
then would provide a cleared site suitable for
redevelopment into a community parkland
and open space.
Some demolition in the area had already
been carried out, but three
redundant 15 to 17 storey tower
blocks, Melrose, Peebles and
Selkirk, remained. RCH decided
to demolish these three blocks
as part of its regeneration
strategy for the area. In order
to demolish the 50 m (164 ft)
high structures, a demolition
contractor was sought with the
necessary expertise to carry out
all aspects of the complex site
operations.
After a rigorous tendering
process in August 2012,
Safedem was employed a principle contractor
to execute all aspects of the blowdown and site
clearance works for the project.
The Belville Street multi-storey blocks in
Greenock’s city centre had dominated the
city skyline for over 40 years. The structures
were built on a significant slope that created
a split level ground floor. The slope was such
that the structure was 19 storeys on the north
elevation but just 16 storeys on the south. A
single lane 2.4 m (7.9 ft) access road known
as Serpentine Walk bordered the structures
to the north – the only separation of the
structures from a 40 m (132 ft)
drop down a sheer rock face. At
the base of the rock face and just
14 m (46 ft) from the structures
on plan was the main electrified
west coast railway line.
CONSTRUCTION
Each of the three towers
were approximately 32 x 20
m (98 x 66 ft) on plan, and
approximately 60 m (197 ft)
high. The construction was
of reinforced concrete and
shear wall construction with concrete floors.
The shear walls were unusually thin at just
100mm (4 inches) thick, making the stability
calculations for Safedem’s pre-weakening
works extremely challenging. Presented with
such structural issues there was only one
option – pre-weaken less and drill more (or
longer) holes.
The structures were further complicated
as they consisted of two offset
wings on either side of a stiff
centre core area that housed the
lifts and stairwells.
BLAST DESIGN
Given the close proximity of
the nearby rock face combined
with the difference in heights
at ground level, Safedem’s
explosives engineer, William
Sinclair, had to design a
collapse mechanism that would
defy gravity by dropping the
structures up hill. To combat
the difference in ground levels, he pushed the
lowest blast floor up to the building’s 5th floor,
calculating that the lower floors would crush
down and act as a cushion for the collapsing
structure above. To direct the structure up
hill, delay detonators were used to encourage
the structure to ‘walk’ away from the railway
line and come to rest up the hill. The direction
and rate of collapse was precisely controlled
with a total of 6,300 delay detonators ranging
from 100 to 2,200 milleseconds. This range of
delays effectively broke up the 40,000 tonnes
of structures during the collapse in order to
The Belville Street tower
blocks just before the
triggering of the charges
