This 420m long multi-faceted retaining wall structure is comprised of three, and in one section four walls at this upmarket shopping mall. Over 46 000 blocks, which were designed to allow for curved walls, were supplied to cover S-shaped walls spanning a combined total of 2 570m2.
Despite the walls’ eye-catching attributes, public safety rather than aesthetics was the prime motivator for shoring the embankment with terraced walls.
Wall construction was complicated because it was undertaken while the centre was fully functional. This restricted the working area and a section of the parking basement adjacent to the embankment had to be used for temporary storage of the excavated soil.
Detailed logistical planning was required to counter the restricted working space and a ramp was built to provide access to the upper wall sections. Besides excavating and stockpiling the soil, an existing precast concrete drainage channel, which ran along the bottom of the embankment, had to be temporarily filled to provide adequate and unimpeded access to the lower wall section. Provisional drainage was installed in this section during construction. Dust was another problem and the on-site ground water was used to damp down the soil.
Although the embankment soil was sufficiently stable for backfill purposes, particular attention had to be paid to drainage due a water spring in one section of the embankment, which ran continuously. Sub-soil pipes were placed at the bottom of the cut face and outlet pipes were run from the cut faces to the bottom of the walls. Sausage drains were placed against the cut faces of the upper walls and the outlet pipes drained onto the flower beds of the lower terraces. M100 piping was used for drainage where the water flow was at its heaviest.
To ensure that the walls were structurally sound and well drained, low-fines concrete was used for the backfill material of the lower wall. This wall varied in height between one and three metres and, in one three metre section, the wall was built around a substantial quantity of rock.
The upper walls were built to between one and two metres high at an angle of 80˚ and all had concrete foundations. Excavated soil was used as backfill material for the upper terraces which were reinforced with WG4 geosynthetic. In addition, a layer of bidem was installed under the second to last layer of blocks on all the walls for erosion protection.
The CRB blocks were also used to construct two staircases to provide access to the terraced gardens.
