Major Project in One of the Most Expensive Cities in the World


Classified as one of the most expensive cities in the world, Luanda is the capital and largest city of Angola, a former Portuguese colony in south-west Africa. Conditions have been gradually stabilizing since the end of the Civil War in 2002, and reconstruction is in full swing – thanks also to the country’s vast mineral resources. Building work is in progress all over the country.

BAUER Spezialtiefbau GmbH from Schrobenhausen, Germany, has been active in Angola since 2002 and established BAUER Angola Ltd. in 2007. The company is currently working on a number of projects, the largest of which is the Teatro Avenida, a residential and business complex in the center of Luanda.

The 20-storey building will incorporate five levels of underground parking, several floors of office space and apartments, and a gym. The ground floor and first floor will house a theater and other entertainment facilities. Bauer Angola has been involved in the project right from the preparatory phase, among other reasons because the existing 42 m deep excavations were insufficient. The base of the foundation piles put out to tender lies as much as 51 m below ground, and nothing was known about the soil directly beneath the foundation level. Consequently, four holes down to a depth of 55 m were drilled prior to starting the contract, and two pile tests under twice the working load (2 x 550 t) were carried out as final preparations.

For the actual building foundations 220 piles in lengths of up to 31 m were produced. The excavation base of the underground levels extending down to a depth of 21 m necessitated corresponding empty bores, so the bores had to be sunk down to depths of up to 51 m. Two BAUER BG 28 rigs were deployed. Then 10 m of casing (1180 mm) was set, down to 32 m depth dry-drilled using a drilling tool (1060 mm). Down to the final depth the bore was supported by bentonite slurry. After sand, stone, silt and clay, the bottom layer – again comprising sand – contained confined ground-water. This is influenced by the Atlantic Ocean, which is just 300 m away, so all the piles had to be constructed from the current surface level.

At present the 44 staff – working day and night – are using a BAUER GB 60 grab unit to construct 6000 m2 of diaphragm wall (800 mm thick, 30 to 33 m deep) as a temporary retaining wall for the basement levels. The diaphragm wall is being tied back by almost 900 anchors in 19 to 24 m depths, using a KLEMM KR 806 and a BAUER UBW 06. Anchor sleeves are being built in to the reinforcement cages of the diaphragm wall in order to prevent subsequent coring of it.
All the anchors have to be executed below the ground-water level. To finally lower the ground-water, six wells will have to be sunk at a depth of 23 m each.

The project – Bauer Angola’s largest to date – is scheduled for completion in August. The next major contract, involving the foundations for seven bridges, has already begun.

Source: BAUER Spezialtiefbau GmbH

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