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DECEMBER • 2016
Construction
WORLD
30
Civil Engineering and Building Contractors (outside South Africa)
A
3
The Senqu River Bridge Project involved the con-
struction of a four span, 140-metre-long composite
steel and concrete bridge over the Senqu River in
the Quthing district of Lesotho, near the town of
Mount Moorosi. Two kilometres of approach roads
linking the Phamong and Quthing districts were
also constructed as part of the project.
SENQU RIVER BRIDGE PROJECT
The Phamong district is situated in a very rural, isolated area in the
southern regions of Lesotho. For many years the only access for
the people of Phamong to the bustling business district of Quthing
was to cross the Senqu River by ferry or on foot.
When the mighty river is in flood, which can be for up to four
or five months of the year, there is little or no access. The building
of this facility was therefore essential to give the people of
Phamong access to vitally needed goods and services from
the Quthing district.
The Senqu River at the project’s location is approximately
150 m wide and has a large sand bed up to 25 m deep in some
places. When the river is in full flood, up to 2 500 m
3
of water
hurtles down between the river banks. For this particular reason,
the design of the bridge dictated a solution which required the
launching of large steel girder truss sections across the river,
followed by the casting of a 250 mm in-situ thick concrete deck
with New Jersey parapets. The four spans of the bridge vary in
length between 30 m and 40 m.
The bridge substructure consists of two abutments situated on
the banks of the river and three piers up to 15 m in height situated
within the river bed. The substructure is founded on 1 100 mm
diameter oscillator piles which vary in depth between 8 m and
22 m which are socketed into the bedrock. The bridge has four
spans varying in length between 30 m and 40 m.
In order to execute the piling and construct the piers, a temporary
rock fill causeway was constructed across the river, which allowed
the dry season river flow to pass through unabated. Access to
the pier foundations for piling and construction equipment was
via this causeway. Due to the large seasonal floods which occur
in the wet season, it was essential that the pier foundations were
constructed during the dry season.
The bridge deck consists of three 2 m deep steel girders laced
together with cross bracing and a 250 mm thick, 12 m wide in-situ
concrete slab cast on top of the beams with in-situ New Jersey
parapets constructed on the sides of the deck.
Twenty metre sections of the three steel girders were pre-
assembled on the launching platform situated behind the eastern
abutment and launched in phases across the river. Launching was
done with the use of two 150 ton jacks mounted to the east bank
abutment with 20 m being jacked out over the river at a time.
The composite steel and concrete deck structure in
combination with the elongated T section piers set against the
back drop of the vast Lesotho mountain range makes for a visually
appealing landscape.
The 2 km of approach roads have a surfaced width of 9 metres
with the layer works generally consisting of a G7 lower and upper
subgrade, a cement stabilized G5 subbase and a G2 crushed stone
base. The Cape seal surfacing consists of a 13,2 mm aggregate
seal and fine slurry.
Local labour working on the project were employed from the
areas around Mount Moorosi and Phamong.
Employees were also educated on life skills, HIV awareness
and environmental awareness. Once the project is complete,
all employees will be issued with a certificate confirming there
involvement in the project and the exposure and training in the
above mentioned areas.
Some 38 000 shifts have been recorded with no lost time
injuries. Given the location of the project and the limited
construction knowledge of the local community working on the
project, this is a remarkable achievement.
Project information
• Company entering: Stefanutti Stocks
• Client: Lesotho Roads Directorate
• Start date: 20 March 2012
• Project end date: 5 October 2015
• Main contractor: Stefanutti Stocks Lesotho
• Consulting engineers: SMEC Consulting
Engineers in association with
Elite Consulting
• Subcontractor: Pennyfarther Engineering
• Cost of project: M150-million
(Lesotho Maloti)
Highly Commended