Who we are

Henri Vidal, a French architect and engineer came up with a revolutionary idea of developing a new composite material using earth as a raw material. After five years of establishing the theory for his process and completing experiments on scale models, he filed the patent for Reinforced Earth® in 1963. Since its invention, Reinforced Earth® has found wide use in many different areas of civil engineering, notably in retaining walls, seawalls, dams, bridge abutments and foundation slabs.

The following three fundamental elements make up the patented general configuration of the revolutionary Mechanically Stabilized Earth (MSE) wall system.

1. Backfill: controlled frictional backfill materials
2. Reinforcement: steel or geosynthetic soil reinforcements that are attached to a modular facing system
3. Facing panel: facing systems vary and may consist of concrete panels, wire mesh, vegetative surfaces or semi-elliptical metallic panels

Reinforced Earth was established and started operations in Johannesburg, South Africa; at the time there was less than 100 000m2 worldwide (now over 50 000 000m2).

1st Reinforced Earth® structure in South Africa at Silvermine. A retaining wall on the corner of a sports field behind Westlake Golf Course – Cape Town.

Protective walls built in 1977 covering approximately 35000 m2. A contract given to Reinforced Earth for protective shelters at a military Air Base.

The Terre Armee Group’s second coal storage bunker was constructed at the Chewes Uranium Plant near Stilfontein in 1978. A representative from RESA, the EPCM engineer and the pre-caster all visited the first bunker, at the Kerr McGee Mine near Gillete Wyoming prior to its construction.

Tweepad was constructed in 1979 using ribbed steel reinforcing strips for the first time. The overall height of the structure is 42 m. The RHS facing the structure is tiered with 15 m lower and 27 m upper vertical walls. Henri Vidal the inventor of Reinforced Earth stood on top of both Table Mountain and Tweepad. He said that of the two Tweepad was the more impressive.

During January 1978, after exceptional rain a section a section of split-level dual carriageway highway on Road P39.1. near Krugersdorp, South Africa collapsed. At the failure the road was on a steep gradient as it climbs an escarpment. The road was constructed partly in cut and partly on fill, on a natural side slope of about 1 in 2. The failed section was about 60 m long and the lower carriageway dropped about 6 m. The failure was extended about 150 m down the slope, at which point the slide debris formed a tongue approximately 200 m wide.

It is revealing to note a sharp anticline situated beneath the road. The dip of the shale in the zone through which the failure was assumed to pass, changed from about 45 degrees on the exposed cut face to about 60 degrees at the outside edge of the excavation.

A number of structural solutions were considered ranging from a bridge across the gap to a row of large diameter piles tied back into the face and supporting a cantilevered deck. All these solutions were excessively expensive. A Reinforced Earth structure about 16 m high and 115 m long on the shoulder edge of a realigned carriageway provided the most economical and rapid solution.

The constituent materials:

Backfill: Sand was available from a commercial source 6 km away

Reinforcing strips: The strips, of maximum  length 11.5 m and minimum 4.5 m were galvanized steel with cross sections of either 40 mm x 5 mm, or 60 mm x 5 mm, with projecting ribs

Facing: Precast concrete panels 180 mm thick and overall panel size 1.5 m square each a with mass of about 1 tonne

The structure was instrumented at a section 16 m high with strain gauges, pressure cells and pull- out strips.    

The bridge carries the N1 freeway over a minor road and was constructed in 1980. The reinforcing strips are 60x5mm mild steel, high adherence, hot dip galvanised with yield stress – 250MPA and ultimate stress – 350 MPA.

The durability of the reinforcing strips was monitored after 11 years and again after 37 years.

In 2017 the average loss of thickness after cleaning was 15 microns per side and 10 microns per side after stripping of zinc. No pitting corrosion or loss of strength was evident.

For the rehabilitation of Rietvlei Dam near Pretoria a physical hydraulic model study of the by-wash spillway was conducted to help in the comparison of various options. The options included lowering the FSL with 2.2 m, raising the crest, widening the spillway and combinations of the latter two. Lowering the FSL would have reduced the effective storage by 31% and was not considered a long term feasible solution. It was concluded that widening the spillway and raising the NOC wit approximately 3 m would be the best option. The design for the raised wall required that there be a amount of flexibility in the completed structure and the designers found the Reinforced Earth method of retaining wall construction ideally suited for this purpose.

The Institute of Civil Engineers presented its National Award for the Most Outstanding Civil Engineering Achievement of 1990 to the Northern Access Route (Km 0 – Km 56) to Katse Dam in Lesotho. The road includes the 3 000 m high Mafika Lisiu Pass over the Malutis, one of the highest mountain ranges in Southern Africa.

In order to facilitate easier passage of heavy vehicles through the 15 m radius bend a 50 m approach section was reduced from an average road gradient of 14% to 5%, with a grade of 2.5% through the bend. The total road width of 8 m was increased to 14 m.

In order to accomplish this geometry a 130 m long Reinforced Earth retaining wall was designed. The maximum height is 18 m. The tight 22m radius of the facing elements and the height of the wall required that it be tiered to ensure the necessary flexibility of the  facing elements. The reinforcing strips are HA steel. The weather in the Malutis can change in minutes to rain, hail or mist. The local weathered basalt backfill from just above the structure originally to be used was too wet and due to daily showers could not be compacted at optimal moisture content. Consequently a free draining crushed doleritic basalt backfill was borrowed from a pit at the foot of the pass.

 The approach embankment to the Malibamatso  Bridge has  slopes which would be submerged by the Katse dam. These had to be battered back from 1.5:1 to 2.5:1and then picked up vertically with a  6 m high TerraTrel  faced Reinforced Earth structure to attain the original grade of the road.

The road to the Pelaneng Adit crosses a high embankment with a large ARMCO culvert. A tiered Terratrel faced Reinforced Earth structure provided cost savings by reducing the culvert length.

First application of Reinforced Earth® in a Quay Wall Structure – Richards Bay.

In order to extend the quay in the dry in the future – a 16 m high cut off Reinforced Earth structure was constructed at the same time as the quay, When the quay is extended the Reinforced Earth structure will serve as a dam wall to allow the extension to take place in the dry.

Just North of the Tropic of Capricorn, in Botswana, a TechSpan™ bridge has been erected over the main rail route from Gaborone to Francistown in just 4 days. This is the first TechSpan structure in Africa.

The design comprises a three-hinged arch with footings on either side of the railway line. The precast concrete elements weigh up to 13 t each, and two mobile cranes were used to position the elements. The span of the bridge 7,6 m and the rise 6,3m, to accommodate a single trach of the Botswana Railways making provision for future electrification. Each element is 2 m wide and the overall length of the structure is 30 m. The ends are scalloped or tapered from the height of the structure down to the ground. The wing wall is not an arch, but acts as a propped cantilever, which is positioned into a concrete slot. All the vertical joints were sealed with geofabric strips, When all the segments were in position a ring beam was cast to prop the top end of the wing wall  elements. A crown beam was placed along the top of the structure to tie in the elements longitudinally.

The 35 precast elements were cast in South Africa and transported by 12 trucks into Botswana. Cranes with a lifting capacity of 50 t were needed to be on-site off-load the trucks and then to proceed with the construction.

Once all the elements were in place and ring beams are cast backfilling to provide a metre coverage over the top began. Backfill should not be able to go up more than half a metre higher on one side than on the opposite side because of the nature of the structure. Crusher dust was used for three metres on either side of the structure. Beyond this normal backfill was placed.

An innovative concept for the widening of fills over an existing side fill has been implemented on the National Route 2 (N2) across the Great Kei River in the Eastern Cape Province of South Africa.  Ten retaining walls have been constructed in which soil nails are combined with a Reinforced Earth structure to allow for the accommodation of traffic during construction, widening of the fills and compliance with overall stability requirements. This solution economically satisfies the technical and environmental requirements and has potential to be used more extensively for widening projects in the future. This innovation was the first time that  an embankment slope was “linked” to a Reinforced Earth structure now branded in the Group as TerraLink®.

The northern side of what is locally known as the Kei Cuttings, comprises a road characterised by high, steep cliffs on the upslope side of the road and long relatively steep embankment fills on the downslope side. This torturous, steep and dangerous section of the road required widening to enable safe passing and adequate sight distance. Cutting into the high upslope cliffs would be both impractical and costly so that any widening would have to take place on the downslope side.

Following discussions between all parties an innovative and economical solution was proposed. This solution required a combination of a nailed system and a much narrower Reinforced Earth mass.  A typical cross-section of the composite soil nail and Reinforced Earth structure is shown. This solution allows for the accommodation of two-way traffic; limits the excavation required for the RE mass; satisfies the internal stability requirements of both the temporary nailed structure and the RE structure, the composite nailed / RE structure and also the overall stability requirements of the widened embankment. Finally, it provides a pleasing natural visual appearance.

Desalinated sea water is pumped over 50 km from the Atlantic seaboard to the mine situated in west- central Namibia.

Constructed in 2009, Trekkopje Uranium Mine’s reservoirs have proved the benefits of Reinforced Earth® technology. Successfully withstanding the Namib. Fast track construction was a key consideration for going the Reinforced Earth route, plus the need to counter aggressive corrosion and elevated temperatures.

The design brief called for the building of six adjacent and interconnected reinforced concrete water retaining structures complete with concrete roofs. Each reservoir was to have a capacity of  9Ml, making the total capacity 54Ml. The project needed to be completed in eight months.

One of the tenderers, Target Projects offered an alternative solution. This consisted of two 27Ml units composed of Reinforced Earth walls with lined vertical inside faces and a 1V:2H outer embankment slope. The sidewalls and floors of the containment area would be covered with an impermeable geosynthetic liner.

The alternative concept also provided for a rigid concrete roof. The roof requirement was subsequently omitted by the client. The alternative was accepted for the following reasons.

• Shorter completion time
• Simpler process to dismantle and rehabilitate at the end of the mines life
• Vertical sides to accommodate a rigid roof structure (although not subsequently adopted)
• Cost advantages
• Flexibility and suitability for poor founding conditions

Reservoir geometry

The original water depth of 6,5 m was retained giving a reservoir size of 64.5 m x 64.5 m x 6.5 m deep . The overall depth of 7.5 m (0.5 m freeboard and 0.5 m embedment) was the maximum height.

Constituent materials

The facing was non-reinforced concrete, the joints were sealed.

A synthetic strip (GeoStrap) was connected to the panels by way of  synthetic sleeves (GeoMega) cast into the panels providing a fully synthetic connection

Locally available sands were used for both the common and RE backfill

Design

Internal and overall stability, drainage and hydraulic considerations were addressed.

Follow up:

After the initial pilot stage ended in 2013 full-scale production at the mine was mothballed pending optimal economic conditions. Reservoir water is being used  for drinking water, mine maintenance and leach pad trials. No leaking has been detected from the reservoirs after seven years of operation.

 Since the reservoirs are not covered the loss of water is solely due to evaporation which is approximately 2m per annum at the mine. The lining appears to be in good condition and no maintenance or replacement lining is envisaged in the foreseeable future.

The compressible panel is a simple method of increasing the flexibility of a precast concrete cladding and has been successfully used on numerous high tip walls.

Two channels fastened to the back of the panels with cast in bolt sleeves allow for handling and placing the panel into the structure. Once the reinforcing strips have been attached to the whole panel, the upper half panel bolts are removed. The upper half of the panel is now free to settle and rotate relative to the lower half of the panel.

Very heavy loading on top of the side-walls required a coarse free draining backfill and a flexible TerraTrel cladding. Galvanized steel reinforcing strips were used, not only in the RE mass, but also as base reinforcement to tie the bases of the walls from splaying.

With the expansion of Reinforced Earth South Africa into Africa, it was imperative that got more people on the ground and what better city to open a satellite office than the Mother City itself, Cape Town.