Civil Engineering December 2021 | Vol 29 No 11

Civil Engineering December 2021 33 K night Piésold was appointed by eThekwini Municipality’s Water and Sanitation Unit (EWS) as the consulting engineers for the design and construction supervision of a proposed 30 Mℓ rectangular reinforced concrete reservoir at the Emoyeni Reservoir site. The site is located in Hillcrest in the Outer West region of the eThekwini municipal area. The existing Emoyeni Reservoir was a 5 Mℓ circular, reinforced concrete reservoir which was supplied by a DN500 offtake off the Western Aqueduct, a major supply pipeline running from Pietermaritzburg to Durban. The water demand from the res- ervoir supply zone has grown to the extent that the old reservoir was no longer able to meet the EWS standard for bulk water storage of 48 hours. A new 30 Mℓ reservoir was therefore proposed by EWS adjacent to the existing 5 Mℓ reservoir. CAPACITY In the inception stage of the project it was determined that a 30 Mℓ reservoir could not be accommodated in the space available at the proposed site. It was initially decided that a 30 Mℓ would be constructed but the old 5 Mℓ reservoir would be demolished. The reservoir site is in a densely popu- lated residential area. Following a stake- holder meeting, the residents adjacent to the site disapproved the size and proximity of the structure to the site boundary. The reticulation system was modelled using Bentley WaterCAD software and the future demands introduced to the system. Following a 48-hour simulation it was determined that the reservoir size could be reduced to 25 Mℓ, excluding the old 5 Mℓ reservoir. This resulted in a smaller footprint with more space between the structure and the surrounding houses and required the demolition of the old reservoir. In order to keep the system live, the reservoir would be constructed in two chambers such that the old reservoir could continue to operate while chamber 1 was being constructed. Only once chamber 1 was complete and commissioned could the old reservoir be demolished and chamber 2 constructed. The overall size of the reservoir is 98 m long × 34 m wide × 8.2 m high. 4 m of the reservoir is below ground level and 4 m above ground level. The limited space available on the site posed a challenge. With a 5 m deep excavation required, and only 2 m to 3 m of working space around the structure, a normal battered excavation was not pos- sible. The excavation required the slopes to be vertical and an earth reinforcing system in the form of earth anchors, wire mesh and gunite was designed in conjunc- tion with the geotechnical engineers. STRUCTURAL DESIGN The reservoir design deviated from the standard designs historically used by EWS. Instead of multiple movement joints in the floor and walls, the design called for no movement joints in the walls to prevent leaking. Swellable water stops were chosen for the floor joints as a cost- effective and simple means of enhancing water tightness. There is a movement joint between the main dividing wall of the two chambers. In order to mitigate the shrinkage cracking resulting from the lack of movement joints, additional reinforcing was required. Another innovation was to use a uni- form wall thickness as opposed to tapered walls. This resulted in the wall mid-height crack width reducing from 0.17 mm to 0.15 mm for the uniform wall. A UNIQUE DESIGN The design and construction of the Emoyeni Reservoir utilised unique design and construction methods. The success of the project, specifically the water tightness of the finished product, makes it worthy of recognition within the industry.  SANRAL SA I CE 2021 Nat i onal Awards Category: Techn i cal Excellence FINALIST Technical Excellence category (Sponsored by Maccaferri SA) KEY PLAYERS Client: eThekwini Municipality Consultant: Knight Piésold Contractor: Afrostructures Construction of 25 Mℓ reinforced concrete reservoir The new Emoyeni Reservoir Uniform wall thickness was used instead of tapered walls