Civil Engineering October 2021 | Vol 29 No 9

Civil Engineering October 2021 33 PROJECT DETAILS AECOM was involved from inception through to the design stage, construction monitoring and close-out. Construction commenced in September 2017 and the project was completed in November 2020, on time and within budget. The design proposal recommended the replacement of the existing problematic sewers with the following: Q Q 1 245 m HDPE-lined concrete bulk sewers (DN 900 mm to DN 1 000 mm) Q Q 3 094 m GRP bulk sewers (DN 350 mm to DN 600 mm) Q Q 1 486 m uPVC collector sewers (DN 110 mm to DN 355 mm). The detailed hydraulic design was done using PCSWMM modeling software and the pipeline material design was done according to manufacturer availability, client preference, resistance to sulphuric acid attack and suitability to site condi- tions. The selected materials and size combinations are proven technology for sewers and will offer a long lifetime. The project also included: Q Q 94 concrete manholes Q Q Two above ground gravity-flow sewer pipe bridges (DN 350 and DN 1 000) across the Plankenbrug River, including associated river hydraulic modelling Q Q Two temporary sewage pump stations (300 ℓ/s each) and one temporary screening station for sewage over- pumping around the construction works Q Q Reconstruction of a 150 m long × 4 m high river retaining wall to protect the new sewer Q Q Stormwater intercept structures to di- vert polluted stormwater and low flow runoff from the Kayamandi township into the sewer network and not to the downstream Plankenbrug River Q Q Installation of bulk sewers by means of no-dig methods underneath live provin- cial roadways and railway lines (90 m microtunnelling DN 1 170 mm, 40 m pipe jacking DN 1 050 mm, 50 m hori- zontal directional drilling DN 250 mm) Q Q Reconstruction of 900 m municipal roadways following sewer installation underneath Q Q Two open-cut railway line crossings. Environmental and social governance improvements following completion of the project included: Q Q A reduction in pollution previously caused by sewage leaking and over- flowing into the river Q Q Interception of polluted stormwater runoff from the Kayamandi township will improve the river water quality Q Q A reduction in health risks to the local community as extremely high E. coli counts were observed in the river water prior to the new sewer implementation Q Q During Phase 3 of the works, the con- tractor was only allowed to ‘clear and grub’ using labour-intensive methods. In addition, all unskilled labour was local, providing employment oppor- tunities, increasing skillsets and work experience Q Q The new bulk sewer will unlock upstream housing development oppor- tunities, which there is a high demand for in this area. AECOM approached the design of the new sewer in a systematic manner, according to best practice sewer design codes, including Stellenbosch Municipality’s own design guidelines. Regular meetings and workshops were held with the client to ensure design expectations were met. Due to the challenging terrain, a total of six route options for Phase 2 were Existing sewers along the Planken­ brug River were replaced The pipe bridge was designed to withstand the force of water in the event of major flooding