Franki – changing the skyline of Luanda

Over the years Franki has done some landmark geotechnical work, providing interesting, innovative and often brilliant solutions for a vast range of differing geological conditions. But few are more special than its recent work in Luanda, Angola where it has completed several projects on 5-million year old relic beaches, where the sea has receded and where the building occurs at various levels on these ancient beach slopes. Each position brings with it its own unique geological challenges and appropriate solutions. This story is about two of these current projects.

 

Franki’s connection to the first project, Total E&P Office Tower, goes back at least three years when it was appointed by the client, Bayview, to do the technical investigation and to assist in the preparation of the foundation investigation report and preliminary design for the lateral support and piled foundations. The project then went out to tender two years ago.

 

Franki was not successful. Its resources, at that time, were tied up on two major projects in close proximity to the Total Office Tower, which meant factoring in the costs of bringing in new resources and machines resulting in Franki being knocked out on price.

 

The project was awarded to a well known European competitor to Franki in Angola, which completed the installation of soldier piles, but its proposed foundation piling solution was not suited to the geotechnical conditions and its contract was terminated.

 

So, Franki was called in again and successfully negotiated with the client and main contractor, Soares Da Costa – whom Franki had met eight years previously when work first commenced on the Torres Atlantico project, also in Luanda - to redesign the foundation solution and expedite the works to recover the circa two months lost time.

Franki, with its prior knowledge of the conditions through its original design input, opted for the piled solution outlined in its initial geotechnical support documentation. “The Continuous Flight Auger (CFA) pile was the optimal solution for these conditions and with the equipment now available, we were able to successfully complete the pile installation and to contribute significantly to bringing the project back on track,” says Franki technical director Gavin Byrne.

 

He adds that the completion of the lateral support that had been partially completed by the previous company was also part of Franki’s contract. “Here it was necessary for us to redesign the anchor tie-back,” says Byrne.

 

503no x 650mm diameter CFA grout piles with a working load capacity of 2250kN have been installed on the Tower block and parking area. 58no Titan micropiles are currently being installed on the Utility block of the project. 155no, 52/26 Titan lateral support anchors have been installed for the lateral support on the project.

 

The soil comprised dense, fine and medium beach sand to depths in excess of 40m and the pile depth, an average of 16m, was determined by the load capacity requirement and the overall settlement limitations required by the Tower block.

 

Rod Schultz, director of Franki África Sucursal Angola, says that one of the challenges on this job was the partially constructed building on the site, which was commenced before the Angolan Civil War and ultimately abandoned with a basement and its piling structure intact. “We had to accommodate the piles that had been installed for this project in our foundation solution and geometry,” says Schultz.

 

Byrne says that another challenge has been the differing cross-cultural design practices. “Countries have differing standards, which must be taken into account. In this case, there were some significant complications with respect to varying interpretations of the validity of the design.”

 

Ultimately, it was agreed, that to verify the design and to help solve the problem, Franki would constantly monitor the settlement of the structure on a regular basis. “Thus far the pile performance has been completely validated,” says Byrne.

 

With the second project, the Kinaxixi MXD Complex, Franki also has a long history, in particular with the Korean project management team, Space Group, the main contractor, Soares da Costa and the Korean professional design team. As with the Total E&P project, Franki did the geotechnical investigation and assisted the professional team in the design of the lateral support and foundations for the project.

 

The Kinaxixi MXD Complex is a large development the size of a city block in Luanda comprising commercial, retail and residential space and up to five basements for parking. The main body of foundation work involves lateral support for excavation depths up to 25m below ground level.

 

While the geology of the Kinaxixi site is similar to the Total E&P site, it is not identical because it is positioned on the plateau above the Total site. “This site is characterised by a semi-continuous band of hard rock Calcrete/Sandstone up to three metres thick,” says Schultz.

 

Franki proposed a two-stage excavation operation. The first comprised a soil-nailed solution for the upper six metres followed by a soldier pile and anchor lateral support for the remaining 10 to 18-metre deep excavation.

 

Schultz says that this solution was developed to eliminate the costly and time consuming drilling of soldier piles through the hard rock Calcrete/Sandstone evident in the upper six metres of the soil profile.

 

“The old, uncharted services, mainly on the east excavation face, are quite a challenge on this job,” says Schultz, “but the biggest challenge is to accommodate the unforeseen elevated and localised saturated soil conditions and we have put forward an alternative to cater for these conditions.

 

The lateral support design was modified for these unforeseen conditions and we are currently awaiting approval to mobilize jet grouting equipment to install soil cement columns between the soldier piles to stabilise the excavation face.”

 

The final phase of the project is the development of a foundation solution for the tower block structures. Two options - raft or piled foundation - are currently being evaluated by Franki and a decision will be taken once it has determined the in-situ soil compressiblity and strength parameters on the relevant portions of the site.

The completed phase of the project comprises 1150 no soil nails, 4,200 square metres of gunite and 310 no micropiles and more than 370 soldier piles. The remaining work on the second phase comprises the installation of up to five rows of Titan anchors and 7,500 square metres of gunite arches and possibly 90 jet grout columns.

 

Byrne says that Franki’s wide product range and innovative approach have resulted in appropriate and economical foundation solutions for these contracts. “Each solution is different for each project as are the modification and installation processes which suit the unique conditions of each site,” he concluded.

 

Franki Africa – of which Franki África Sucursal Angola is a subsidiary -  is part of the JSE-listed Esorfranki group. The company’s capabilities,include piling, soil-investigation, lateral support, ground improvement, micropiling, grouting, cut-off walls and marine works. It has more than 40 production rigs and a staff complement of more than 900. With respect to cross-border work, apart from in Angola, where it also pioneered a new method of jetty construction in Luanda harbour, it is active in other African countries and the Indian Ocean Islands, where it also used its unique jetty construction for the Seychelle’s Fishing Authorities..

 

 

Issued on behalf of:                                                  

Esorfranki Limited                                                     

Tel: (011) 822.3906                                                   

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Contact: Ms. Tammy Davies                                                 

Website: www.esorfranki.co.za