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Installation of Concrete Step Barrier, The benefits of collaborative working
The refurbishment of the catenary lighting between junctions 29 and 30 of the M5 was undertaken in early 2007 as part of the Area 2 EMAC (Enhanced Managing Agent Contract). It was the most demanding scheme, in terms of concrete extrusion, completed under the EMAC to date. By virtue of the underlying contractual ethos, the EMAC provides opportunity to improve established practice and to reduce costs by the reduction of waste.
The existing catenary lighting columns had been protected by steel barrier in the central reserve.Some of these columns were to remain and be protected by Concrete Step Barrier (CSB); others were to be relocated in the verge. There was also an over bridge, the supports of which were to be protected by Higher Vertical Concrete Barrier (HVCB).
Hanson have selected PJ Davidson (UK) Limited,(PJD), as supply chain partner for Area 2 works and it was established that ‘Best Value’ would be achieved if Hanson managed the interface with the client, material supply and other contractors and PJD provided the site expertise for the works processes. By early involvement of the extended supply chain, most significantly Hanson Premix, numerous innovations and ideas were explored that ultimately benefited the project. These included options for forming the base of the wall and the provision of an extruded slot drain that provided increased capacity whilst requiring less installation space.
Key risks were identified and the following mitigation measures agreed upon:
- Traffic disruption to concrete deliveries during peak hours – The two Hanson premix plants supplying agreed to supply over a 12 hour shift; Honiton for the days, Exeter for nights and Saturdays. PJD worked similar shifts with an hour overlap to ensure continuity during handover periods.
- Acceptability of concrete – To avoid potential delays on site whilst concrete mix details were refined, an area for trials was made available off site on Hanson premises. PJD have experienced significant delays whilst concrete mix designs are refined to allow for local variations in grading of regional fine or coarse aggregates. To emphasise the importance of this issue, Hanson appointed a Technical Key Account Manager to liaise with PJD to minimise wastage.
- Access for delivery vehicles - After establishing that the concrete would be delivered from Hanson’s Exeter and Honiton plants with an emergency back up from Tiverton, access points were placed to enable easy access to the works from junctions 29 and 30 and from the M5 North and Southbound. Meetings were held with all delivery drivers presenting details of routing, timing of activities, wash out procedures and access and egress details.
In total, the base and wall required 4,420m³ placed over a period of twenty days.
Works on site commenced with the hand laying of the wall foundation on Saturday 17th February. Concrete was supplied at 24m³ per hour which optimised production and minimised waiting time for delivery wagons. Over the next three days, 1,400m³ were laid.
Over the course of twenty working days, 2,020m³ of foundation and 2,400m³ of wall concrete were supplied to produce 3,034 linear metres of foundation, 6,070 linear metres of CSB and 270 linear metres of HVCB. On completion of the central reserve, 62 in-situ concrete lighting column plinths were cast together with transitions, contraction joints and bifurcations, using another 176m³ of concrete.
Overall, only 33m³ or 0.72% of concrete was rejected from the wall works, of this only 12m³ was returned to the Hanson Premix plants; the remainder was used on site. This equates to a wastage factor of only 0.24%.
Regular liaison between Hanson Premix and the site team of Hanson and PJD personnel, ensured changes to the programme or scope of the works were managed effectively to mitigate adverse influence on cost and duration.
The works were completed to time and to budget. Improvements and innovations were made to established working practices that reduced wastage and provided certainty of outcome for the project.
The standard of finished product, in terms of profile, line and level, exceeds specification and provides a good advertisement for the concrete extrusion process and the collaborative working methods adopted.
For more information, contact Tim Doyle at tim.doyle@area2.interroutejv.co.uk