When Edgard Frankignoul invented the Franki pile in 1909 he had no idea that 110 years later it would still be regarded as one of the most cost-effective and reliable solutions for a host of different geological conditions.
“It’s quite amazing,” says Franki Africa’s Gavin Byrne, “that with only relatively small improvements over time, the Franki pile, after so many years, repeatedly remains the solution of choice in a wide variety of conditions. Given that we operate in an ever-changing and advancing technological environment makes the ubiquitous nature of the Franki pile even more remarkable.”
“Above all, the Franki pile is a unique system for generating excellent load capacity and we have developed a number of techniques to install it in a variety of soil conditions,” adds Byrne. “With its wide range of pile sizes and its characteristic enlarged base, it’s fair to say that the Franki pile has been one of the cornerstones of Franki Africa’s success in southern Africa.
The latest project to demonstrate the magic of the Franki pile is the piling work done for Sappi at its Saiccor mill in Umkomaas, KZN.
Sappi’s project includes the installation of a new evaporator, recovery boiler and screening and washing plant, along with upgrades to the bleach plant and pulp machines, improved recovery circuits and additional magnesium digesters. The piling tender for all these elements stipulated the installation of approximately 1900 piles to varying depths.
Difficult Ground Conditions and Record Depths
“I would say that the ground conditions on this site were among the most difficult in Franki’s 75 years of installing piles in the Southern African region”, says Byrne. “From our initial design and construct perspective, we had no doubt that the Franki pile would be the most cost effective and technically robust solution for a variety of reasons.”
The fact is the conditions actually encountered on site revealed even greater variations in the geological profile than was expected. Not only would piles have to be installed at depths of 24m – an all-time record for the company – but installation would also have to be performed at very shallow depths of between of 5m -8m.
Byrne says it is not only this significant variation in depth that was challenging but also how quickly the founding depth changed. “Over large parts of the site the founding depth would vary by as much as 15m. This was perhaps the single most challenging condition of the site and necessitated very careful site planning and fast and constant evaluation of the deeper areas of founding to ensure that the heavy equipment could be continuously utilised.”
In a nutshell, Franki has had to deal with some of the shallowest conditions it has ever dealt with juxtaposed with the deepest it has ever had to deal with and the Franki pile proved to be exactly the right solution. “This is mainly because the Franki pile accommodates a wide variety of difficult founding conditions and provides remarkable settlement performance and load capacity”, explains Byrne.
Not the end of the Franki pile’s advantages
One of the stipulations was that the piles had to resist uplift forces. Franki’s Jonathan Day, who was instrumental in the final design of the job, says any other pile like, for example, auger or CFA piles, would have been a much more expensive and complicated solution due to these piles having to be socketed into the bedrock. “The Franki pile’s large base is the best solution in this regard mainly because it can be founded on the rock surface while providing superior uplift capacity,” he says.
Two more site conditions reinforced the choice of Franki piles. Firstly, there were boulders at localised portions of the site at various depths and Franki piles are able to penetrate the boulder horizon. Secondly, across the majority of the site there are very soft silty clays and the Franki piles are ideal for driving through such material with the Franki pile casing preventing collapse of the material and ensuring the integrity of the pile shaft concrete.
A wide range of equipment for the job and the timing challenge
A total of six piling rigs are being used on the job. These include three standard Franki crawler piling rigs for the shallower piles, an Ajax 55t crane with leader for the piles to about 17m, a 70-ton Liebherr for the 18m -20m piles and the recently introduced large Liebherr crane ( 90t) for the deeper piles including Franki’s deepest, history-making piles of 24m.
Day says that the timing has been one of the important challenges of the job. “Our client required certain key milestones to be achieved and set stringent targets for each section of the job. In this regard I am pleased to say that we have completed the first sections on time and on budget. The excellent relationship between ourselves and our client Sappi has been fundamental to the success of the project thus far,” he concluded.
Meanwhile Errol Braithwaite, Franki MD, says that he is proud of the quality projects that Franki is currently involved in, especially in this very challenging economic climate. “There is no doubt that the construction industry in Southern Africa is facing one of the most pressured periods in its history – many companies are having to reinvent their business models, some will close, foreign companies are entering the market, skills are exiting the market and confidence is down.
“In spite of this, however, I remain confident about the future. In our own organisation we are still experiencing a buoyant order book and, importantly, we are seeing excellent young talent emerging which is more representative of our diverse nation than ever before. Through our parent company, Keller Group plc – the largest independent geotechnical construction company in the world – we have unprecedented access to international expertise and technologies and, with Keller, Franki has a local presence in African cities stretching from Cape Town to Nairobi, from Accra to Mauritius and many places in between.”
Franki Africa has a long history of success on the African continent and its experience and expertise have been greatly bolstered by being part of Keller with which it shares all the values that will enable Franki to continue giving its clients a world class service.
“We are fortunate to have some of the best people, technologies and equipment on the continent and it is our responsibility to continue delivering excellence across the board to all our customers,” Braithwaite says.
He adds that perhaps Franki’s most important attribute is the quality of customers, like Sappi, it has attracted over the years. “This has been a privilege of the highest order and I am pleased to be able to express our gratitude to them out loud and in public.”
Published in the April 2019 edition of the SAICE Civil Engineering Magazine