Dulce Simoes Dredging, Excavation, Jet Grouting, Marine Works, Piling

Geotechnical work in the marine environment demands creative solutions to complex challenges. That’s the nature of the game and there is no one better at it than Franki Africa, which has developed a reputation throughout Africa for its innovative and cost-effective solutions. It is interesting that in both the below marine projects, one of the common themes is great teamwork – a perennial Franki skill!

 Project 1: Dormac Quay Wall

The first project is the construction of a 180m-long, 16m-high (4m above water and 12m under water) quay wall for marine engineering company Dormac’s new floating dock at their marine works facility at their Bayhead, Belfast Rd site in Durban. Shipping is renowned for tight schedules and high operational costs and this project is subject to the same pressures in order to meet the schedules of the future users of the dock.

Franki Africa’s Paul Pearce says that this has been a complicated, multifaceted contract. “Although it is one structure, it has required many highly specialised geotechnical skills for a successful outcome,” he says.

One of these skills was specialised jet grouting using a rig from Franki owner Keller’s German division. “In fact the cooperation between Franki and Keller Germany was most helpful,” says Pearce, “and confirms the supreme advantage that we have being part of the Keller network and able to tap into the best technology and equipment in our industry.”

He adds that the jet grouting was a highly technical and complicated operation requiring top-end management, operators and support “After a 3-week training and test phase, the jet grout operations began and, after some initial hiccups with Franki Cape Town coming to the rescue with their experience in jet grouting, we were able to source the faulty parts from Europe and continue with a productive and successful operation,” Pearce says.

There have been a few significant challenges on this job with the first, as expected, having to working in tidal conditions and being exposed to the moods of the ocean. The Franki crew worked around the clock to accommodate tidal movement and, operating when they could, they laid down a high-spec working platform for the piling rigs. “This was an exacting job to say the least,” says Pearce, “but when it was complete we were able to work with the sea being kept at bay and the biggest risk to our operation allayed.”

The second challenge from a piling perspective was the positioning and tolerance of the piles in relation to the jet grout columns. “It was critical to get the positioning spot on to ensure a vertical face to the quay wall,” Pearce says. “Our works department came up with a very innovative idea in the manufacture of special guides and frames to assist us in placing the piles in accordance with the fine tolerances and this worked perfectly.”

Piling challenge number three – to increase our piling production rates – was as a result of Dormac’s request for Franki to complete the contract two and a half months earlier than initially agreed to. “This required some fleet-footed action and we decided to purchase new, more efficient equipment specifically for the Dormac contract. Our Plant division put in a sterling effort with the new machinery, going way beyond the call of duty to fine-tune the machines and to train the operators. The end result was that we were able to sufficiently increase our production,” Pearce says.

Another major challenge still to come is the installation of two 1800mm diameter mooring pawls which are part of the integrated dolphins for the floating dock attachment. With extremely tight tolerance to accommodate the tidal movements of the dock and the sheer scale of the pawls, this will also require an exceptional effort from the Franki team at Dormac.

The quantities on the Dormac job tell the story:

230 no. x 900mm diameter CFA piles 24m deep; 180no. x 800mm diameter jet grout columns 16m deep; 180m long x 5m high quay wall capping beam; 1500m x 63mm diameter tie bars; 80 000m³ dredging and excavations; 6000m² new dock yard surface with services.

Pearce says that Franki is concluding installing the capping beam and are currently busy hanging the facial panels on the quay wall. “This has been a challenging project but we are proud of our ability to work in marine conditions – a skill that we have acquired throughout the company over many years. Apart from knowledge and experience, the most important ingredient for jobs of this nature is teamwork and we had that in abundance on this job,’ concluded Pearce.

Job 2: P.E. Jetties

In September 2014 Franki Africa’s Cape branch was appointed, on an Alternative Design, as sub-contractor to Haw & Inglis on the PE Lead-in Jetties Contract, which comprises two components:

  •  ŸA 40-ton slip converted into a 90-ton boat hoist jetty comprising two sets of connecting jetties of 16 bays each; and
  • Two lead-in jetties for the 1200-ton slipway consisting of a Northern Jetty (with 30 bays) and a Southern Jetty (with 39 bays).

Franki was responsible for the entire pile installation operation, whilst Haw & Inglis undertook the concrete deck structure in accordance with Franki’s design.

According to Franki divisional director, Roy Louw there was a concern about the effects of vibrating through the 4.0m seabed, drilling a 1.5m rock socket and having a crane walking out on to the jetty before the concrete had gained sufficient strength. “For this reason we finally decided to install 610mm diameter piles using the Rotapile or ODEX method as this would be the least risky and would also allow quicker access. I’m pleased to say that this decision certainly proved to be the correct one”!

But this meant ‘back to the drawing board’ – quite literally – for alternative design and drawings and the design of the single tube guide-frame. At the same time Franki requested permission to proceed with the soil investigation, as the last one was conducted on the quay way back in 1975, and no geotechnical information was available on the lead-in jetties.

In early January 2015, the Franki Durban team commenced with a geotechnical investigation and the results were totally unexpected! The seabed was found to be 3.5m – 6.0m thick with a boulder layer of 12.0m – 18.0m thick before the bedrock was encountered. This completely vindicated the decision to opt for the ODEX piling method!

With the soils information available a test pile to 3 000kN, twice the working load, was undertaken. “With the test pile passing with flying colours, we proceeded with the pile installation, now only required to be 9m deep below the seabed with a minimum 3m socket into the boulder layer,” explains Louw.

As the team became more adept at drilling into the boulders, productivity increased significantly. It managed to complete the 30 piles on grid-lines A and B on the 90-ton boat hoist at an unprecedented rate, coming from 22 days behind the programme to only 8 days.

In the beginning of August 2015 piling commenced on the Northern Jetty of the 1 200-ton slipway, which was completed on the 5th of November 2015, 13 days ahead of programme. The equipment was quickly transported over to the Southern jetty and the installation momentum was kept at a high standard. Piling to the Southern jetty was completed on the 9th of March, a staggering 53 days ahead of programme.

“This has been a monumental team effort,” says Louw. “From the management of the complex contractual issues to the safety management and the welding team and everyone else this team raised the bar in terms of performance,” Louw concluded.