Construction World February 2019

Projects under the section flanked by the wall, using precast concrete culverts. The wall was built by simply sandwiching three six metre long panels between two 3 m high galvanised steel beam sections. Two of the panels were 120 cm wide and were positioned above Natural Ground Level (NGL) yielding a wall height of 2,4 m. The third or anti-trenching panel was 600 mm wide and was installed below ground to discourage people from tunnelling under the wall. This panel rests on two reinforced concrete footings at each end of an installation bay and supports the two slabs above it. The footings measured 1 m x 1,8 m x 400 mm (depth) and were cast on 450 mm re-compacted cement-stabilised soil. The beam sections were delivered to site with base plates and flanges already attached. After being bolted onto the footings, laser levelling was used for vertical alignment of the beam sections. Thereafter the panels were slotted between the beam sections by truck-mounted crane. Each panel was 120 mm thick as opposed to the beam section channels which were 150 mm wide. This left a gap of 30 mm which was filled with non-shrinking grout. Wooden wedges were used to hold the panels flush against one of the inner sides of the beam sections to facilitate the grouting process. After three days the grouting had cured sufficiently for the wedges to be removed and the remaining gaps caulked. Echo Group marketing director, Melinda Esterhuizen, says there are several advantages to this type of walling, speed of construction and cost being major considerations. “Eight to 10 bays or 48 to 60 linear metres were completed daily (eight hours). A conventional masonry wall would have taken two to three times as long with no advantage gained in strength or durability. In fact, because our panels have a compressive strength of 50 MPa, they are virtually indestructible,” said Esterhuizen.

A partially completed section of the wall in which Echo’s smooth soffits and the close-fitting tongue-and-groove jointing are seen to good effect.

Byron Haarhoff, managing director of BKH Construction, adds that Echo’s panels come with smooth soffits and don’t require maintenance. “They also have a tongue and groove jointing system to ensure that adjoining panels form a tight seal. Moreover, Echo cut out 200 mm x 200 mm sections at each end of the anti-trenching panels to ensure a snug fit over the steel flanges which provide additional support for the steel uprights. “Before actual site-work commenced we worked hand-in-hand with local businesses and community members, acquainting them with what the work would entail and using their input on the recruitment of local labour. We always use local community members in all our projects and in this instance we upskilled locals on concrete compaction, the drilling of bolt holes, bolting, grouting and the type of steel we were using for the uprights,” concluded Haarhoff. 

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CONSTRUCTION WORLD FEBRUARY 2019