JG Afrika, a leading South African engineering consultancy, appointed by main contractor Leomat Construction jointly devised an innovative approach to swiftly and cost-effectively replace a treated-process water pipeline from Tugela Mill to a discharge point on the Tugela River that had reached the end of its design life.
Notably, the Sappi Mandeni Treated-Process Water Pipeline Replacement Project received an award for technical excellence in the South African Institution of Civil Engineering’s regional awards programme.
Developed in 1945 to produce container board and lignosulphonate for the export market, the mill is one of Sappi’s oldest purpose-built operations and remains a significant employer in-and-around the town of Mandeni, KwaZulu-Natal.
Tugela Mill’s treated-process water pipeline was previously transferred via a 1m-diameter underground pipeline over a distance of 3,5km to the effluent discharge point on the Tugela River, while also passing through the suburbs and parallel to the Mandeni Stream.
The pipeline was showing signs of fatigue and Sappi, therefore, issued a design and construct tender to completely replace the existing pipeline.
Importantly, the existing pipeline had to remain operational until the new infrastructure was completed to avoid any production disruptions at the mill. The transition from the old to the new infrastructure would then have to be finalised within a nine-hour shutdown period.
Moreover, the new pipeline had to follow the existing route as closely as possible to comply with environmental requirements. This is in addition to being constructed within 3m of the existing infrastructure to ensure that all the construction works were undertaken within the current 8m-wide servitude.
It also needed to be sized to accommodate a flow rate of 50Ml of treated effluent per day.
Sappi decided to adopt a design and construct approach to accelerate the project delivery by eliminating additional supply-chain processes and enabling the contractor to procure pipe materials while the detailed design was being finalised. This, most notably, mitigated project risk quickly and made the main contractor the single point of responsibility.
Importantly, this method would ensure close collaboration between the client, as well as the JG Afrika design team and contractor, while also creating an environment that encouraged experimentation and invention by all representatives of the professional team.
From the outset, the focus was on devising a high quality, yet cost-effective solution that would reduce any potential environmental and reputational risk in an extremely short timeframe, maximise efficiencies and mitigate the impact of construction activities.
Neal Bromley, a JG Afrika Technical Director, says that the firm benefited from this approach by being able to incorporate Leomat Construction’s wealth of construction knowledge, including in terms of buildability of the pipeline and construction techniques, into its designs at a very early stage to ensure a positive outcome.
“It was the bold step of appointing Leomat Construction and JG Afrika by Sappi that provided the space the professional team needed to be innovative and creative. The solution was conceptualised at tender stage and modified and developed throughout the course of the project according to prevailing conditions,” Bromley says.
JG Afrika and Leomat Construction were awarded the contract to replace the treated-effluent pipeline based on their innovative approach that entailed replacing the aged treated effluent pipeline in two distinct phases.
The new pipeline was first completely constructed and commissioned above ground and laid within the servitude. This permitted the treated effluent to be transitioned from the old to the new infrastructure in a very short timeframe thereby alleviating most operational risks associated with the continued operation of the old pipeline.
The Class 10 high-density polyethylene pipeline (HDPE) pipe was butt-welded in 12m-long sections to create robust and durable joints. This enabled the pipe to be pressure tested and commissioned in only six months versus an estimated 18 months that it would have taken using conventional trenching methods.
The second phase entailed “re-excavating” the old pipe trench to remove and recycle the existing steel pipe. Thereafter, the new pipeline was lifted and relayed into the trench.
This approach provided significant cost savings considering that all of the rock had already been removed when the original pipeline was constructed, while the bedding and blanket placed under and around the old pipeline could also be reused.
Sappi’s specification for HDPE piping material and the slightly reduced hydraulic capacity from the outset played a large part in facilitating this unique solution. As an extremely flexible and durable material, the pipe could be double-handled by the main contractor without the risk of damaging it.
Calculations undertaken by JG Afrika during the tender stage also indicated that the pipe diameter could be reduced from the initially proposed 1m to 800mm due to a reduction in the volume of treated effluent over the years through various process improvements. This, in turn, would also facilitate the use of existing pipe sleeves for crossings in critical areas to provide further cost and time savings for the client and reduced public inconvenience.
The many pipeline crossings required innovative thinking by both the design and construction teams. Crossing of the one arterial and three residential roads were completed during the first phase of the project.
Certainly, one of the biggest challenges and highlights of this component of the project was crossing Old Main Road which runs outside the mill and serves as the main entrance road into Mandeni.
The professional team initially intended to use the existing steel pipe under the road as a sleeve for the new infrastructure and, in so doing, eliminating the need for pipe-jacking or excavation. However, a camera inspection revealed that this section of the pipeline was clogged by a large quantity of rocks and stones.
The team had to think on their feet to avoid delaying the project. The existing steel pipeline was removed, and the new HDPE pipeline fed through the existing concrete sleeve. The new pipe was then welded to the pipeline above the ground on either side of the road. This entailed careful planning and coordination as there was very little scope for error.
Another challenge was the crossing at the Mandeni Stream. The pipeline was first laid along the bank and up against the downstream face of the weir until it reached the opposite bank. It was then temporarily anchored to the weir to ensure that it did not wash away during any storm events. Leomat Construction was then able to cut open the crest of the weir and remove a portion of the steel pipeline encased inside. The balance of the steel pipe was used as a sleeve for the new HDPE pipeline.
The professional team received significant praise from Sappi for its innovative approach, as well as the high quality of its workmanship which was completed on time and budget.