Dry weather flow interceptor, Tai Kok Tsui, Hong Kong

Dry weather flow interceptor, Tai Kok Tsui, Hong Kong

NEC has been adopted to deliver a dry weather flow interceptor and pumping station at the outfall of a large storm drain in Tai Kok Tsui, Kowloon, Hong Kong. Substantially completed in October 2022, the complex HK$106 million (£11 million) project helps to improve water quality and mitigate odour in New Yau Ma Tei Typhoon Shelter and West Kowloon coastal area in Victoria Harbour.

The Drainage Services Department (DSD) of the Government of the Hong Kong Special Administrative Region engaged a joint venture of China Metallurgical Group Corporation and Top Express Construction Engineering Limited to build the interceptor under an NEC3 Engineering and Construction Contract (ECC) Option C (target contract with activity schedule) in December 2017. DSD’s harbour area treatment scheme division was the NEC project manager, with Binnies HK Limited acting as the NEC project manager delegate and NEC supervisor. 

The work involved building a three-storey sewage pumping station and nine 4.8 m wide, 3.5 m high penstocks across the Cherry Street box culvert where it discharges into the typhoon shelter. The pumping station wet well, screen chamber and valve chamber were constructed in a deep sheet-piled excavation in reclaimed land next to the sea. To save time, most concrete elements were manufactured off-site and lifted into position using a 400 t floating crane. Despite challenging working conditions and supply chain inflation, the project was completed on time and within budget. 

Cherry Street box culvert collects storm water run-off, the majority of which is polluted, from most of the busiest areas of the Kowloon peninsula. During dry weather, the new penstocks now divert the flow via a new pumping station to Stonecutters Island sewage treatment works, effectively preventing the pollution load from entering the typhoon shelter. The contract included constructing a new 85 m long waterfront promenade above the interceptor, which opened in December 2023. On account of its innovative design and delivery, the contract won the NEC Water Project of the Year award in 2020.

Contractual partnering

DSD now uses NEC Contracts for most of its infrastructure procurement programme following a successful initial trial in 2012. According to DSD Senior Engineer Paul Law, ‘The NEC requirement to work in a “spirit of mutual trust and co-operation” leads to contractual partnering and close communication between all parties. Together with the NEC early warning and compensation event procedures, this helps resolving problems and differences that would otherwise have developed into disputes.’ 

He says the ECC target cost option was chosen for the project for four reasons. ‘The scope of works was well-defined, the contract allowed a fair risk sharing between the employer and the contractor, it provided an incentive for the contractor to save cost and achieve early completion, and DSD’s successful experience in using Option C on two previous projects provided us with confidence.’

Law says the project faced various challenges and risks, not least working in a congested waterfront site measuring just 1,650 m2. ‘At the beginning of the project, the forecast of the final price for work done to date was increased as the returned tender prices of the sub-contract works were higher than that in the activity schedule. This immediately led to a pain situation.’

He says two special task forces were then set up to ensure smooth project delivery and keep pain shares to a minimum. ‘A senior management task force was established to resolve intricate problems as quickly as possible. It also enhanced the payment mechanism to deduct the pain shares by monthly increments and to reduce the risk of payment disputes among all parties.’ 

Adopting innovation 

cherry2.jpgDSD Engineer Bernard Chan says a risk-to-opportunity (RTO) task force was also set up to propose the adoption of innovative ideas and other ways to enhance performance. ‘The aim of the RTO task force was to achieve mutual objectives including early completion, cost savings and zero accidents. Its proposals were implemented under NEC compensation events with joint effort and support from the project manager, the supervisor and the contractor in a collaborative manner.

He says examples included the use of design for manufacture and assembly for most of the concrete elements. ‘The project adopted the concept of off-site fabrication followed by on-site installation. This arrangement reduced activities in the congested site, relieved pressure on labour resources, allowed originally sequential activities to be done concurrently and enhanced product quality.’ 

Chan says another example was the novel use of a new desilting robot. ‘Over 400 m of the existing culvert was found to be silted up, which could affect the penstock installation and delay completion of the interceptor. The RTO task force proposed using DSD’s new remote-control robot to assist the silt clearance, which minimised the duration of hazardous entry by workers and avoided dry-season-only working. The hydraulic performance of the drainage system was quickly and cost-effectively improved.’

He says another innovation was artificial-intelligence monitoring. ‘Site activities were monitored in real time to identify any hazardous moves by workers, particularly during the Covid-19 pandemic. This significantly improved the safety performance on site, resulting in zero accidents.’

Chan concludes, ‘Although this project was full of challenges and risks, the project team embraced the NEC “spirit of mutual trust and co-operation”. By collaboration with the suppliers, subcontractors, future maintenance parties, utility undertakings, adjacent residents and operators, we were able to overcome the challenges and risks together, completing this environmentally beneficial project on time and within budget.’

Project highlight video

Benefits of using NEC

  • NEC requirement to act in a ‘spirit of mutual trust and co-operation’, resulted in contractual partnering and close communication between all parties. All contracting parties were working as a team under an amiable and trustworthy relationship.
  • NEC early warning and compensation event procedures helped to resolve potential problems disputes before they materialised. These greatly reduced the chance of cost overrun and project delay.
  • ECC Option C provided fair risk sharing between the employer and contractor and incentivised the contractor to save cost and achieve early completion.
  • Despite physical and financial challenges, NEC-inspired collaboration helped ensure the project was delivered on time and within budget.
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