replacement of corroded metalwork within the valve tower to
improve safe access
at Digley IRE - Courtesy of MMB
Impounding Reservoir (IRE) is located in Holmbridge,
Huddersfield. The valve tower associated with the reservoir had
corroded access metalwork which did not meet current health and
safety standards. The project replaced all the corroded access
metalwork within the valve tower with new Yorkshire Water Asset
Standard compliant metalwork, improving safe access within the
tower. The scheme also included application of a paintwork
system to the existing pipework, valve spindles and support
beams. A 3D laser scan of the valve tower was undertaken to
prevent repeated visits into a confined space and to aid the
Yorkshire Water Services
(YWS) has over 130 impounding reservoirs (IREs) which have deep
shafts/valve towers that require regular internal inspection.
Due to their age, the access arrangements within the valve
towers do not meet the modern health and safety standards.
Design and build contractor Mott MacDonald Bentley (MMB) was
awarded a delivery contract to address access issues within the
valve tower at Digley IRE. The valve tower at Digley IRE is
approximately 44mm deep and is circular in shape with a diameter
of 3.8m. There are eight intermediate levels in addition to the
top platform level and scour tunnel invert level. The reservoir,
including the valve tower, was built in late 1940s/early 1950s.
Health & Safety
The significant health
and safety issues that were addressed at the design stage and
during the works included:
Working at height.
Working in a confined
Working adjacent to deep
Working on steep slopes
and uneven ground.
Due to the nature of the
work, the entire scheme was about improving the health and
safety and access issues within the existing valve tower. To
eliminate the need for repeated entries into a confined space,
and in the interest of health and safety, MMB employed a
specialist subcontractor to use the cutting-edge technology of
laser 3D scanning throughout the entire depth of the valve
tower. The 3D scan created a point cloud where the distance
between any two points could be measured by using 3D-compatible
computer software. The accuracy of the scan was +/- 5mm.
All the new metalwork was
fabricated utilising the 3D scan which prevented a need for
taking manual measurements within a confined space, cutting
short the entire process by weeks. This had commercial and
health and safety benefits, by increasing efficiencies and
reducing design time, whilst maintaining high quality standards.
The 3D scan will also add value to any future schemes related to
this particular site by visually accessing the inside of the
valve tower and taking any required measurements from the scan
without having to visit site. A 3D model was generated for the
final metalwork design of the valve tower to visualise and
discuss the proposed design with YWS project managers and
operational team, ensuring real ‘buy-in’ to the project from all
Whilst carrying out the
metalwork installation work on site, MMB employed a specialist
subcontractor specialising in emergency rescue in confined
spaces, working at height and safety management so that the
proposed works were carried out in a safe, controlled manner.
Temporary scaffold platforms were used to dismantle the old
metalwork, install new metalwork and apply the paintwork system
to existing steelwork within the valve tower. All MMB personnel
who were involved in site activities were confined space-trained
and CSCS qualification holders.
Traffic Management was
employed in the form of half lane closure across the crest road
for loading and off-loading construction material. Local roads
and the crest walkway were kept clear at all times for local
public and dog walkers.
Internal 3D scan of the valve tower
Courtesy of MMB
External 3D scan of the existing valve tower
Courtesy of MMB
There were several
constraints and challenges that MMB has faced at both the
detailed design stage and at the installation stage:
Provision of a bespoke
man riding davit: The current YWS operational strategy is such
that there is provision for one entrant into the valve tower
with one top man - however, going forward YWS wish to facilitate
entry for two personnel into the valve tower with a top man.
To meet this change, MMB
procured a bespoke man riding davit which has provision for two
entrants accessing the shaft one after another. The davit is
supplied at the top platform level and can be removed when not
in use. A flush davit socket is supplied which is fixed to the
new metal decking at the top level.
There are two winches
supplied with the davit which have fall arrest as well as
retrieval capabilities in the event of an emergency.
Achieving a straight lift
out of the valve tower: The old access arrangement in the valve
tower was such that the access ladders were staggered at every
platform. This meant that the entrant could not be pulled up to
the top platform level in an emergency.
The new metalwork design
was undertaken in such a way to achieve a straight stretch of
ladders all the way down into the shaft to facilitate emergency
rescue. The 3D scan proved very helpful to achieve this.
Damp environment due to
leaks and water ingress into the valve tower: the lower levels
of the tower were excessively damp; it proved very difficult to
apply a paintwork system to the existing steelwork at the lower
levels when the old metalwork was removed. To overcome this
problem, MMB employed heavy duty ventilation equipment to force
ventilate the shaft and reduce the moisture level for
application of the paintwork system.
model of the gantry levels within the valve tower
(right) 3D model of the base of the valve tower -
Courtesy of MMB
In order to reduce the
impact on the local residents in close proximity to the
reservoir, no work was planned outside of ‘standard’ working
hours. There were no noise or vibration issues as all the work
was carried out within the valve tower away from local private
properties. As part of YWS standard procedure, a customer
engagement plan was produced for this scheme, with customers
living in the local vicinity of the reservoir contacted prior to
the commencement of works to inform them of the proposed
The scheme fulfils the
YWS sustainability requirements which are actively pursued as
part of YWS strategic business objectives and performance
commitments for AMP6 projects. All the decommissioned metalwork
that was recovered from the valve tower has been collected in
skips and will be widely recycled, and a site waste management
plan (SWMP) was produced by the principal contractor as part of
the project. Where possible, structural elements including
support beams associated with the access metalwork were retained
and applied with a specialist paintwork system to extend their
design life in damp, corrosive environment. The success of the
scheme is down to excellent teamwork and collaboration between
all parties involved in its delivery.
and publishers would like to thank MMB for providing the
above article for publication.
MMB would like to thank Lee Laherty, Project Manager, and
John Bond, Communications Advisor, both with Yorkshire Water
Services for their input.