Design and Construction of the Emoyeni Reservoir by Knight Piésold for eThekwini Municipality, KwaZulu-Natal

COMMENDATION Design and Construction of the Emoyeni Reservoir by Knight Piésold for eThekwini Municipality

The design and construction of the Emoyeni Reservoir was unique in that several aspects in both areas deviated from previous designs and construction techniques.

Traditional structures incorporate several movement joints to allow for movement and shrinkage of the concrete while still maintaining water-tightness. The client (eThekwini Municipality) had used this concept design for most of the existing reservoirs in and around the Durban area. The problem with these designs is that they relied on the construction of the joints and specifically the water bars to be undertaken correctly. Any errors or movement of the water bars during the concrete pours result in the water-tightness being compromised. This has resulted in many of the existing reservoir developing leaks.

For this design, Knight Piésold decided on a different approach, doing away with the movement joints in the structure. As this was a very large concrete structure (100 m x 35 m x 8 m), the removal of movement joints required careful modelling. Furthermore, the previously utilised tapered wall width was changed to uniform walls. The modelling of the structure showed that the uniform walls performed better as a propped cantilever with smaller crack width, and made the reinforcing designs at the corners simpler and easier to construct. Construction joints were still required; however, the specification on these was given careful consideration and was closely monitored during construction. Although the steel quantity increased in order to mitigate cracking, this cost was offset against the savings in water bars, as well as the decrease in construction duration and the lower risk of leakage. These design changes resulted in a structure that was commissioned with zero leaks and a high quality of concrete. This large structure was constructed in the heart of a high-income residential suburb with very little working space and with cognisance of issues such as noise pollution, dust pollution and traffic congestion. Furthermore, the existing water storage system that was on-site needed to be operational throughout the contract duration.

One of the unique construction techniques utilised on the walls was to pour the 8 m high walls in a single lift. This was done to reduce the number of construction joints, as well as the construction duration.

PROJECT TEAM

Client: eThekwini Municipality

Consulting Engineer:

Knight Piésold Consulting Contractor: Afrostructures

Occupational Health & Safety:

Engelbrecht and Associates