The tender for this contract closed in July 2012 and was awarded by SANRAL to CMC Ravenna in February 2013. After a post-tender period of negotiation, Franki received an order from CMC in June 2013 and were able to move on to site once casings and tooling arrived from Europe in mid-September 2013. The main civils contract comprises a four-level interchange with the highest bridge being 1600 metres long and 27 metres high. The next level is to be 700 metres long and 18 metres high.
There are four structures which are to be piled with a total of 407 no. 900mm Ø temporary cased, cast-in-situ, friction piles to depths ranging between 22 metres and 34 metres.In addition, there is a total of 28 no. 900mm Ø similar piles for the temporary structures. These structures are for temporary piers which will accommodate incremental launching at an elevated height of 12 metres above the ground for the main bridge which will be jacked from either end to meet in the centre.
At the time of tender we offered two piling alternatives, either one of which would have realised a considerable saving but these were declined by the Engineer. Before any permanent piles could be installed, three O-cell load tests were carried out at various locations across the site. The testing was carried out using the equipment and expertise of Loadtest of the U.K. This turned out to be quite a costly exercise as the Rand devalued by 25% between July 2012 and August 2013.
All of the O-cell pile tests were, as specified, prepared to be tested up to 10 000kN. However none of the tests realised the anticipated loading capacity with the result that the permanent pile lengths were extended by 2 to 3 metres to conform with the design parameters.
Installation of the permanent piles commenced at the beginning of December 2013 using a Bauer BG28 rig whilst a second piling machine, a Casagrande Oscillator rig, was also being set up. By this time, with the delay in procurement of our casings and tooling from Europe and the O-cell testing activities, we were under considerable pressure regarding our initial anticipated programme with the Main Contractor, CMC. At this point, Franki acquired a Bauer BG20 as a more productive alternative to the Casagrande Oscillator. The BG20 was commissioned over the December 2013 holidays and was ready to commence work in January 2014. In addition to the two Bauer rigs, we have established a Casagrande B180 to work in conjunction with the Casagrande Oscillator to complete the raking piles.
At the time of writing, a total of 220 no. permanent piles and 28 no. temporary piles have been installed. Production on the northern side of the site has been reasonable but on the south side, where there is a high water table and soft layers of mud over the lower two-thirds of the pile, additional installation challenges have been encountered. We are, however, slowly progressing out of this area and expect to be able to maintain a more stable rate of production for the remainder of the contract.
The value of this piling contract is approximately R40 million, excluding materials, which are being supplied by the Main Contractor. In addition, there is a further R7,5 million of dynamic compaction, which is 30% complete, and R10 million worth of temporary and permanent lateral support which is about to commence.
It is expected that the piling will be completed by March 2015, with the dynamic compaction and lateral support activities also continuing into 2015 to suit the Main Contractor’s programme.
Jaco Pienaar and Arthur Field