Precast systems that blend in

Unlike monolithic cast in situ structures, the precast concrete products designed for environmentally engineered projects are purpose-built to match the terrain. Two classic examples are permeable pavers and retaining-wall block systems.

The wall reaches up to 7.1 m at its highest point

HARBOUR BAY SHOPPING PRECINCT

Space created for a large parking area

Corner detail as the wall follows site contours

The blocks were placed on a layer works comprising a 100 mm sand fill, 100 mm G5 sub-base and a 50 mm laterite layer

A section of the Terracrete driveway

Permeable precast pavers not only promote effective stormwater drainage, but add an important aesthetic element to low-volume road designs. The installation techniques are also well-suited to labour-intensive construction techniques and SMMEs for a wide range of other project requirements. In addition to residential and commercial developments, these include riverbank erosion protection and steep embankment stabilisations, such as bridge abutments.

“A key feature of hard-lawn pavers is the way they blend in, providing a unique parklike or pastoral effect that adds value to any living space at a competitive cost compared to conventional, impermeable concrete block pavers,” says Holger Rust, founder of precast concrete manufacturer Terraforce. “Within the residential space, this makes our TerracreteTM interlocking hard-lawn blocks equally applicable for affordable housing and upmarket projects.”

Manufactured locally and internationally by Terraforce licensees, Terracrete was introduced to the South African market in 2002 and has a well proven track record for durability. The units, available in varying shapes and sizes, can be laid in different patterns and used with or without ground anchors, depending on the application.

Glen Dirk Estate case study

Terraforce evaluates the durability and sustainability of its installed products on an ongoing basis as part of its research and development programme. A recent example is a site visit to the Glen Dirk Estate in Constantia, Cape Town. Late in 2017, 4 000 Terracrete blocks were installed to form driveway and parking areas. Some three years later, the vegetation is well established, and the system is functioning optimally.

For this installation, the blocks were placed on a layer works comprising a 100 mm sand fill, 100 mm G5 sub-base and a 50 mm laterite layer, cut to shape as needed around corners, and neatly finished with E1 edging. For the grass planting phase, the blocks were filled with topsoil and seeded with Cynodon dactylon, also known as Bermuda grass, which is a hardy, water-wise species.

“Acting as a natural filter, these versatile blocks positively contribute to the biodiversity and ecological value of the area, as well as provide a practical engineered solution,” adds Rust.

Harbour Bay

Soil retention strategies are the mainstay of environmental engineering. Property developments, for example, often require cut and fill slopes that consequently need to be stabilised to prevent erosion by the elements.

A prime example is a project in Simon’s Town, which entailed the construction of a new lifestyle and shopping complex. Built into a hill in the Dido Valley, several steep and exposed cut slopes had to be stabilised. Terraforce’s retaining-wall system was subsequently specified and installed by the appointed contractor, Dassenberg Retaining Systems.

“The platform was handed over to us by Civils 2000 in late 2017,” comments Georg Brand of Dassenberg Retaining Systems. “We then hand excavated the footing and filled it with 25/19 MPa reinforced concrete. The bottom third of the structure was installed with a double skin of Terraforce L11 blocks, which were also filled with 25/19 MPa concrete.”

Added reinforcement comprised Findrain 2 m c/c, Rockgrid 200/200 as tiebacks, and 3% sand-/cement-stabilised backfill. As a result, the Terraforce wall can carry a surcharge of 10 kN/m², 1.5 m away from the top, which comes in at 7.1 m above the parking area.

“One of the challenges we faced on-site was presented by a natural spring situated in the hill above the development,” adds Brand. “A soak-away had to be designed by Fred Laker of ICOS Engineering and a long-time Terraforce wall design specialist to effectively redirect the excess water towards the subsurface drainage. In total, 11 400 Terraforce L11 blocks were installed by our team, expertly overseen by team lead and foreman Rudi De Klerk,” Rust adds.

Finally, landscaping of the wall focused on the water-wise and indigenous vegetation of the area. Today, the sour figs trailing over the top and fynbos shrubs lining the foot of the wall add a softening touch to the retaining systems.

“Greening structures is a growing trend locally and internationally. Here, our systems provide the perfect balance in terms of engineering, aesthetics and the environment,” Rust concludes.

Available in varying sizes and shapes, Terracrete blocks can be laid in different patterns and used with or without ground anchors, depending on the application