Balfour Beatty –Skanska M1 6A–10 Widening
Hydro pumps were employed by the above consortium to carry out bridge deconstruction works to 7 under bridges, allowing for additional carriageways to be constructed.
Works were to remove wing walls and produce stitch lengths in the bridge decks allowing for the extension of the under bridges, utilising Hydro pumps in house plant and operatives for “Diamond cutting, Hydro demolition and Percussion drilling”.
Taking advantage of a package of disciplines, “BBS” elevated the interface between contractors, with Hydro pumps being able to react to changes in program and design, varying the method of removal to suit given situations.
Difficulties encountered include:
- Working over live roads at busy junctions.
- Low head room for temporary works.
- Working to tight programs in conjunction with other trades.
- On site changes in design and reacting to changes quickly.
- Controlling noise.
- Out of hours working.
- Supply of water and delivery logistics.
- Adaptation of plant for specific needs.
Hydro pumps put together a package of operations including:
- Method of removal.
- Type of equipment.
- Programming, method and risk assessments.
- Temporary works (type and method of construction)
- Control of water and arising.
- Re-design of contract to give best outputs, cost effectiveness and end product.
Diamond wire cutting and core drilling
The use of diamond cutting was “Hydro pumps” proposal, and reduced the amount of hydro demolition by over 100%.
Giving both a saving in cost, time and environmental impact (both use of resources, pollution and clean up) comparison 5m³ block requiring 6m² of cutting plus coring has a direct saving of £1,200.00 or £240.00 per m³ along with considerable savings in attendances i.e. water, fuel, clean up and protection.
Any areas were steel retention was not required for reconstruction, were removed by the use of diamond wire.
The areas were cut in to sections; there size to suit the lifting capacity of the crane. The average size was 8 - 15 tons, with a single cut face of 6m². Lifting during possession was necessary in some locations when close to the general public.
Each of the seven structures required an average of 100 – 120m² diamond cutting with the sections being 1300 – 2500mm in width.
Sections required compound angle cutting were bridges were running at a skew to the above carriageway.
Prior to cutting all sections required the core drilling of 100mm lifting holes and 75mm wire insertion holes.
Two types of saw were used a larger computer controlled saw with an output of up to 2-4m² per hour when cutting, and for tight locations a smaller hydraulic manual operated saw with an output of 1m² per hour when cutting.
Removal by hydro demolition was used to form the stitch in the bridge deck and exposed the starter steel in the wing wall were retention was required for reconstruction.
Between 1 and 6 units were used to achieve program, with works being undertaken (at some locations) during a night shift were works clashed with other operations. Each structure required the removal by hydro demolition of between 60 – 70m³.
Work was done with hand lance units, as following assessment of requirements by hydro pumps the use of our gimbaled or robotic system was viewed neither practical nor necessary.
Daily outputs per unit averaged 1.5m³, with 1.7m³ being achieved most days when uninterrupted shifts were possible.
Additional starter bars were needed, these included T40mm bars to a depth of 7000mm in the remaining sections of the wing walls, drilled by small robotic rig.
Drilling using air legs and hand held units in both vertical and horizontal planes for the insertion of 12 – 25mm starter bars depth up to 2000mm.
Drilling vertically with EZ Drill “cradle mounted percussion drill”, for numerous starter bars to a depth of 600mm.
Grouting in of bars Chemical and cementations.
Following removal of the top section by wire cutting and prior to hydro demolition, Hydro pumps robotic drilling rig was used to drill 70mm holes to a depth of 7000mm. Allowing for the grouting in (by our operatives) of T40 starter bars. Drilling of the starter bars was done prior to hydro demolition - A. flat surface to work from B. no interference from bars exposed by hydro demolition.