During the planning of the construction of the City of Cape Town’s Integrated Rapid Transit (IRT) system, which includes the Bus Rapid Transit (BRT) system, Usazasa Road was designated for an upgrade to a dual lane road, owing to the increase in traffic these rapid transit systems would instigate in the Killarney Gardens area.

Contractors Martin & East were responsible for the project, which formed part of the construction of Atlantis Integrated Rapid Transport Corridor – Potsdam Road from Blaauwberg Road to Usasaza Road – and included road works, a new bridge, services accommodation and appurtenant works.

When the contractors excavated the box cut for Usazasa’s new road layer works, they discovered a layer of saturated clay. Due to the poor drainage properties of clay, these water logged sections of the box cut had to be stabilised. A layer of 19mm stone wrapped in bidim A4was selected to drain these sections. In this case, the bidim A4 also acts as a separator, preventing contamination between the selected layers and the clay.

Vehicle or embankment loads increase pore pressures considerably in the soft sub-grade, which decreases the effective shear strength proportionately. Bidim allows the water under confining pressure to pass through into the free draining base materials while retarding movement of particles. Experience has shown that up to50% less fill material is required when using bidim as a separation layer.

Due to the effectiveness of the bidim A4 in performing the separation and drainage roles, relevant sections of Usasaza Road were quickly reinstated, thereby allowing the remainder of the project to continue to completion without interruption.

Bidim has the added advantage of being environmentally friendly as this engineered fabric is 100% produced from recycled polyester cool drink bottles. The bidim content in the Usazasa Road project equates to 56,757 2-litre cool drink bottles.