Construction World September 2020

COVER STORY

FRANKI SUPPORTS THE GREAT

Paving the future for one of the most aesthetic infrastructure landmarks in Mauritius, the Frankipile team achieved another milestone with the successful completion of the foundations for a new iconic ravine bridge. By Roger Feldmann, Business Development, Franki Africa RIVER BRIDGE IN MAURITIUS

L ocated south of Port Louis, the A1M1 bridge – as it is commonly referred to – will effectively connect the areas of Chebel and 6RUª]H RQ HLWKHU VLGH RI WKH *UHDW 5LYHU 1RUWK :HVW 9DOOH\ DQG ͤQDOO\ join the main A1 and M1 arterial roads. The Road Development Authority of Mauritius (RDA) has been planning a bridge to link these two areas on the eastern and western side of the valley for some time in order to ease the growing YHKLFXODU WUDͦF FRQJHVWLRQ LQ WKH DUHD DQG SURYLGH D GHGLFDWHG pedestrian walkway between Chebel and Sorèze. Finally, on 11 April 2018, the government of Mauritius and the RDA launched the construction of the A1 M1 link as part of the larger road decongestion programme. Frankipile Mauritius International, a Keller Company, was appointed by the client to supply and install the specialised piled foundations to support the two piers of the bridge. “The new bridge is based on a classic extradosed design and is the brainchild of Systra International Bridge Technologies,” said Frankipile Mauritius contract engineer and manager, Mirvesh Jugurnauth. “Boasting a bridge deck length of 330 m and supported by two piers towering in excess of 80 m from the river level, the bridge is set to become a national landmark.” The bridge deck incorporates a dual lane asphalt surface for vehicles, a pedestrian walkway on each side and two observation decks, guaranteeing spectacular sunset views over the Indian Ocean. Between a rock and a hard place The comprehensive geotechnical report provided by ARQ Consulting Engineers and the position of the two piers, posed distinct logistical and technical challenges to the foundation solution. Firstly, it was clear that the piles needed to be founded in the hard rock basalt some 18 to 22 m below the river bed level. Secondly, it ZDV HYLGHQW WKDW WKH ͤQDO SLHU SRVLWLRQV ZHUH ORFDWHG LQ WKH ODUJHO\ inaccessible 100-m deep ravine, making it extremely complex for the heavy-duty piling equipment and materials to reach the site. 7KH XQGHUO\LQJ VRLO SURͤOH DW HDFK SLHU SRVLWLRQ UHYHDOHG D combination of silty gravels, colluvium, clay, rock layers and boulders, common in river beds. The pile design called for a total of 40 piles

per pier, and each pile was 1 080 mm in diameter. The piles were designed to carry a working load of 8,85 MN. Through careful coordination and planning with the main contractor (made up of the Transinvest-General Construction Co-Bouygues TP- VSL Joint Venture), the experienced Franki team were able to mobilise the large track mounted piling equipment to the engineered platforms at the pier positions in a safe and carefully controlled manner. Franki used a combination of the powerful Bauer BG20 piling rig to handle the drilling and a Liebherr 845 crane to service the site, weighing in excess of 70 and 50 tons respectively. This robust combination was well suited to handle the installation of the 1 080 mm Ø piles to a depth of 20 m. Belts and braces The Franki team were fully prepared for the anticipated ground conditions. ̸7R RYHUFRPH WKH FRPSOH[ VRLO SURͤOH D FRPELQDWLRQ RI URFN augers, coring buckets and a chisel were used. Where thick rock layers were encountered, a cluster drill was used to penetrate these layers,” explains Mirvesh Jugurnauth.” The cluster drill incorporates QXPHURXV VPDOO GRZQ WKH KROH '7+ KDPPHUV DQG LV VSHFLͤFDOO\ designed to penetrate hard rock. Having both methods available on site enabled the team to reach the required founding depth with relative ease, regardless of the ground conditions.” This “Belts and Braces” approach ensured Franki was able to meet the approved programme and complete the project on time and within budget. 'XH WR WKH XSSHU VRLO SURͤOH DQG WKH KLJK ZDWHU WDEOH WHPSRUDU\ steel casings were used to ensure the integrity of the pile shaft. The piles had to be cast underwater using a gravity fed tremie pipe system. The high slump, self-compacting concrete mix was transported to the pile positions using traditional readymix trucks. In order to meet the tight timeline of the contract, the Franki team worked a double shift each day. “All things considered, and with the strong commitment from the team, the project was plain sailing,” adds Yannis Mongelard, Frankipile country manager.

CONSTRUCTION WORLD SEPTEMBER 2020 20