A new non-dredged technology for Tung Chung East reclamation

The Tung Chung New Town Extension (TCNTE) is the first new town project via reclamation since 2003, following the completion of the last phase of reclamation of the new town development projects in Tseung Kwan O and Tung Chung. The project has adopted the latest environmentally-friendly reclamation technology – the non-dredged “Deep Cement Mixing” (DCM) method, which reduces impact on water quality and marine ecology nearby and takes a shorter time than the traditional reclamation method to complete the works. Last year, the Under Secretary for Development, Mr LIU Chun-san, paid a visit to the reclamation site in Tung Chung and was briefed by colleagues from the Sustainable Lantau Office (SLO) on the details of the new reclamation technology and the eco-friendly construction approach.

Forming 130 hectares of land

The TCNTE project covers the areas on the eastern and western flanks of the existing Tung Chung New Town and reclamation is mainly carried out in Tung Chung East, forming 130 hectares of land, which is equivalent to the size of about six Victoria Parks. According to Chief Engineer of the SLO, Mr WONG Kwok-fai, Alfred, the reclamation works, commencing at the end of December 2017, are in good progress. The first parcel of land formed by reclamation was handed over to the Housing Department for housing development in March this year, a process which took less than 30 months to complete, for construction of about 10 000 public housing units. Besides, an eco-shoreline design will first be adopted along the 4.9-kilometre-long seawall in the project to improve the coastal ecosystem and enhance biodiversity. The whole reclamation project is expected to be accomplished in 2023.

Non-dredged reclamation method

Tung Chung East reclamation is the first public works project using the DCM method for reclamation where no dredging or removal of marine mud on the seabed is involved.

The Contractor’s Senior Resident Engineer, Mr CHEUNG Kin-wai, Chris tells us that the DCM method involves the injection of cement slurry from works vessels into marine mud by “mixing” them together. Each works vessel can carry up to 480 tonnes of cement. In the course of the mixing process, three sets of mixing shafts on the works vessel auger into the marine mud layer, mixing the cement slurry with the soft marine mud while rotating. The marine mud will be solidified to form a strong and hard cement mixing column. These cement mixing columns will form a DCM treatment zone in the seabed to support the seawall to be constructed above and fill materials to be deposited.

Reducing the environmental impact of the works

Senior Geotechnical Engineer of the SLO, Mr CHEUNG Kin-tak, Henry, says in comparison with traditional dredged reclamation method, the DCM method does not involve the removal and transport of marine mud, which can reduce the dispersion of suspended particles in water and effectively lower the impact on the water quality and marine ecology in the nearby waters. In addition, since no sea transport is required for dumping of marine mud, it helps reduce carbon emissions. Taking the works in Tung Chung East as an example, it eliminates dumping of marine mud by 4.4 million cubic metres and marine traffic by 17 600 vessel-trips.

Turning construction waste into land resources

The reclamation project in Tung Chung East includes a recycling element as well. Inert construction waste from construction works is used as the reclamation filling materials, turning waste intended for disposal into valuable land resources. The so-called inert construction waste refers to the construction and demolition materials generated from excavation and demolition procedures during construction, such as concrete, asphalt, stones, etc., which are collectively known as public fill. Currently, the whole reclamation project is about half completed. Regarding the mix of fill materials, 60 percent of the materials are inert construction waste while the remaining 40 percent are manufactured sand. When the reclamation is completed, the final figure is expected to be about 70 percent of the fill materials being inert construction waste with the rest being manufactured sand.

Implementing various mitigation measures

One of the challenges of this reclamation project is how to conduct monitoring and quality management in the reclamation area. Mr Chris CHEUNG says that to ensure there will be no environmental impact from the works, the project team has implemented various mitigation measures, including setting up vertical steel barriers and silt curtains along the periphery of the reclamation site to prevent the outflow of silt particles and to minimise the impact on water quality. The project team has also put in place the Environmental Team and Independent Environmental Checker to conduct seawater sampling and testing regularly for monitoring the water quality. This will ensure that the marine ecology will not be affected. Other mitigation measures include using quality powered mechanical equipment and protective noise barriers to control the noise level generated from the works.

The TCNTE project is one of the major initiatives of the Government's multi-pronged approach to increase land supply in the medium to long term. It will also allow Tung Chung to further develop into a comprehensively-planned new town with a large population capacity and adequate local and regional community facilities. During the course of construction, the project team has been actively communicating with relevant stakeholders, local community and residents, concern groups and green groups with a view to striking a balance between development and conservation for achieving sustainable development.

 
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The Secretary for Development, Mr WONG Wai-lun, Michael, says that the Tung Chung East reclamation works commenced at the end of December 2017 and the first parcel of land formed by reclamation was handed over to the Housing Department for housing development in March this year, a process which took less than 30 months to complete.
The Secretary for Development, Mr WONG Wai-lun, Michael, says that the Tung Chung East reclamation works commenced at the end of December 2017 and the first parcel of land formed by reclamation was handed over to the Housing Department for housing development in March this year, a process which took less than 30 months to complete.
Pictured is the first parcel of housing land formed by reclamation in Tung Chung East (circled in blue).
Pictured is the first parcel of housing land formed by reclamation in Tung Chung East (circled in blue).
The Under Secretary for Development (USDEV), Mr LIU Chun-san (left), paid a visit to Tung Chung last year and was briefed by colleagues from the Sustainable Lantau Office (SLO).
The Under Secretary for Development (USDEV), Mr LIU Chun-san (left), paid a visit to Tung Chung last year and was briefed by colleagues from the Sustainable Lantau Office (SLO).
Chief Engineer of the SLO, Mr WONG Kwok-fai, Alfred says that the reclamation works in Tung Chung East will provide land in phases.
Chief Engineer of the SLO, Mr WONG Kwok-fai, Alfred says that the reclamation works in Tung Chung East will provide land in phases.
The Contractor’s Senior Resident Engineer, Mr CHEUNG Kin-wai, Chris (left), tells the USDEV, Mr LIU Chun-san (right), that the “Deep Cement Mixing” (DCM) method involves the injection of cement slurry from works vessels into the marine mud by “mixing” them together. A DCM treatment zone is then formed in the seabed to support the seawall to be constructed above and fill materials to be deposited.
The Contractor’s Senior Resident Engineer, Mr CHEUNG Kin-wai, Chris (left), tells the USDEV, Mr LIU Chun-san (right), that the “Deep Cement Mixing” (DCM) method involves the injection of cement slurry from works vessels into the marine mud by “mixing” them together. A DCM treatment zone is then formed in the seabed to support the seawall to be constructed above and fill materials to be deposited.
Senior Geotechnical Engineer of the SLO, Mr CHEUNG Kin-tak, Henry, says that the non-dredged method refers to reclamation not involving the removal of marine mud on the seabed, which can reduce the dispersion of suspended particles in water and effectively minimise the impact on the environment while no sea transport for marine mud dumping is required.
Senior Geotechnical Engineer of the SLO, Mr CHEUNG Kin-tak, Henry, says that the non-dredged method refers to reclamation not involving the removal of marine mud on the seabed, which can reduce the dispersion of suspended particles in water and effectively minimise the impact on the environment while no sea transport for marine mud dumping is required.
The Tung Chung New Town Extension project covers the areas on the eastern and western flanks of the existing Tung Chung New Town. Pictured is an artist’s impression of the Tung Chung East extension area.
The Tung Chung New Town Extension project covers the areas on the eastern and western flanks of the existing Tung Chung New Town. Pictured is an artist’s impression of the Tung Chung East extension area.
To ensure that the project will not affect the environment, silt curtains in the picture (shown in yellow) fully enclose the 130-hectare reclamation site to prevent the outflow of silt particles.
To ensure that the project will not affect the environment, silt curtains in the picture (shown in yellow) fully enclose the 130-hectare reclamation site to prevent the outflow of silt particles.
To ensure that the project will not affect the environment, silt curtains in the picture (shown in yellow) fully enclose the 130-hectare reclamation site to prevent the outflow of silt particles.
The DCM method involves the injection of cement slurry from works vessels into the marine mud layer and “mixing” them together. Each works vessel can carry up to 480 tonnes of cement.
The DCM method involves the injection of cement slurry from works vessels into the marine mud layer and “mixing” them together. Each works vessel can carry up to 480 tonnes of cement.
The DCM method involves the injection of cement slurry from works vessels into the marine mud layer and “mixing” them together. Each works vessel can carry up to 480 tonnes of cement.

6 December, 2020

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