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Herolds Bay Sea Wall


Herolds Bay is a small, quaint seaside village in the southern Cape Province. It is known for its sheltered location and idyllic beach, that occasionally comes under attack by the sea in winter. During these months, the homes built close to the beach need protecting from the waves reaching all the way up their front doors and causing flooding and damage.

Herolds bay wall aerial view of beach front

Aerial shot of the Terraforce wall, 2006

Herolds Bay sea wall along the beach front prevents flooding

The Terraforce wall in October 2019!

The existing retaining structures were structurally ineffective and not aesthetically acceptable, and the client, George Municipality, instructed the construction of an improved beach protection wall that would satisfy both structural and aesthetic requirements.

Project team

Engineers: Tuiniqua Consulting Engineers, George Office.
Contractor: New Heights
Terraforce blocks: Mobicast

The new wall in 2019

Herolds Bay new beach front wall

The retaining wall protecting homes close to the beach

Says Paul Goedhart, Pr Eng, Tuiniqua Consulting Engineers, who conceptualised the new wall: “The old Herolds Bay beach protection wall, a combination of various materials and construction techniques, was frequently damaged during winter storms and the Municipality wanted a new uniform wall between the beach and the road which would withstand the sea forces but would also provide an accessible and aesthetic barrier. To meet these requirements a stepped reinforced precast concrete block wall was designed. The wall was founded on the underlying rock since the level of the beach sand varies due to the wave action. In so far this was possible the old wall structure was left in place.

“Where the depth of the rock level was unpractical for normal excavation the wall was built on a reinforced concrete strip footing which was founded as deep as practically possible. A reinforcement fabric was used to anchor the wall to the compacted cement stabilised backfill material behind the wall and enough drainage was provided to reduce hydrostatic pressures. The top of the wall was finished off with an in-situ concrete coping.”

Work in progress on the wall in 2004Construction of the new wall was started in April 2004 and was completed in October of the same year. During that time the team was challenged by high sea levels and high-water table.

 


Goedhart explains why the Terraforce retaining wall system was chosen: “Terraforce L13 blocks were chosen due to the substantial constructed mass that they offer, and 13,500 units were made with a custom-made concrete mixture – 30 MPa with a minimum of 400 kg cement per m³ of concrete – by Mobicast, Southern Cape Terraforce licensed manufacturer. The stepped wall creates an accessible interface between the beach and the roads/lawns. The blocks could also be easily secured together with reinforced concrete and the transition to ramps and stairs was easy to achieve.”

As would be the case with most challenging projects, where few dare to tread, lessons were learned. During particularly heavy storms in 2006 and 2008 some damage occurred to the wall.

 

 

At one point, where bedrock was too deep to be reached, the foundation was undermined, and a small section collapsed. The section was rebuilt on reinforced concrete caissons which were sunk down to the rock level with an added gabion/gabion mattress apron below normal beach level to prevent a new collapse.

At another section, relatively minor damage occurred as a result of the drainage behind the wall proving inadequate to deal with excessive and rapid water ingress. This was easy to fix with the section being reinstalled with better drainage measures. So far, these measures have lasted till today, weathering any further powerful storms.

Withstanding the storms…

 

winter storms at Herolds Bay

Withstanding storms till now!

Terraforce sea wall, Herolds Bay

 

Project team

Engineers: Tuiniqua Consulting Engineers, George Office.
Contractor: New Heights
Terraforce blocks: Mobicast

 

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Terraforce
Reversable hollow-core retaining blocks

4 Huguenot Avenue Oranjezicht
Cape Town
Western Cape
South Africa
8001

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