MOD – Nuttall Refurbishment of Ernesettle Jetty
Hydro pumps were employed main contractors Nuttall to carry out Removal of defective concrete by hydro demolition and reconstruction with spray applied concrete.
The contract was very high profile for both the MOD and public as the jetty is located directly to the side of the Brunel Bridge and was within a triple SI location requiring very high environmental control
measures being instituted and maintained. The contract was subject to a non movable end date as the MOD had ships coming for refit with there movements programmed a year in advance, the jetty was required for unloading of armaments for storage in the facility.
There was a 50% increase in our works which had to be accommodated within the already tight program window.
Works were only able to be carried out during the tidal window; with the increase in quantities it became a necessity to work the evening tide from the mid point of the contract program.
The contract required the removal of 186m³ of concrete from beams columns of soffit areas using hydro demolition and the replacement including increased cover with 302m³ spray applied concrete.
The works were completed within a 20 week program restricted to an average daily 4.5 hour tidal window.
Difficulties encountered include:
- Working within a site of specific scientific interest.
- Working within high visibility and scrutiny of the general public.
- Working to tight program with no possibility of moving completion date.
- A 50% increase in works.
- Sequential removal and reconstruction to maintain stability of structure.
- Working within a tidal window.
- Controlling noise.
- Out of hours working.
Hydro pumps put together a package of operations including:
Consultation
Method of removal and application.
Type of equipment.
Product selection taking into account any environmental impact.
Programming, method and risk assessments.
Development and construction of specific vacuumed recovery unit, allowing for fast cleaning of the scaffold prior to tidal ingress.
Re-design of contract to give best outputs, cost effectiveness and end product.
Hydro Demolition
- Between 2 and 6 units were used to achieve program.
- Hydro demolition was restricted to the day time tide due to noise pollution an average output of 0.4-0.5m³ per unit was achieved during the 4 hour working tilde shift.
Spray Applied Concrete
- 2 – 4 gangs were used to achieve program requirements
- Towards the end of the contract some of the reinstatement was moved to the night tide, so as not to clash with hydro demolition operations and maintain the sequentially removal sequence with elements having to reach design strength prior to further deconstruction
Construction and supply of site specific vacuum unit for operation by Nuttall operatives
Vacuum unit for clearing of site
There was a requirement for fast effective collection of the debris from the under deck scaffold prior to the incoming tide.
To this end hydro pumps have come up with the concept of a vacuum unit utilizing collection bins enabling a large area to be covered without the moving of equipment. The elements of the system are kept as single items to keep down there weight decreasing the point load on the jetty and increase the flexibility of the system.
The collection bins are positioned along the length of the site.
The vacuum power pack is positioned at a suitable location.
50 m of 8” vacuum pipes connect the power pack to the collection bins.
60 m of 6” flexible debris collection hoses transport the debris to the collection bins.
The collection bins hold 1.5m³ each and once filled are emptied via a hydraulic operated flap on the bottom.
The bins can be discharged into either big bag or can have there legs widened to straddle a skip.
Once we had come up with the design concept we went out into the market to do market research as to the capability of available equipment.
Not being able to find any suitable equipment we employed the services of a specialist manufacturer to develop the idea and build us the equipment.
