HKIA Contract 3205 – Deep Cement Mixing Works (Low Headroom)

Project Description

The Third Runway System of Hong Kong International Airport is a project to build a new runway on 650 hectares of reclaimed land north of the existing airport island. The construction of Three-runway System (3RS) commenced in August 2016.

The first phase of works included stabilising the soft mud in the reclamation area by Deep Cement Mixing (DCM) works, installing prefabricated vertical drains and laying stone columns, in order to support the seawall and the newly reclaimed land.

BSGL contract 3205 carried out soil improvement works by low headroom Deep Cement Soil Mixing using the Cutter Soil Mixing (or CSM) method in marine conditions (from barges).

CSM ground treatment is to serve as a stable foundation for the 3RS land formation. Soil is de-structurated by a mechanical tool and a binder (cement slurry) is injected into soft mud to increase strength and stiffness to 800kPa at 28 days strength. This results in a soil treated panel column.

BSGL works spanned between October 2016 and December 2020.

The detailed scope of works involved:

1) Geophysical Surveys; 

2) Supply and Placing of Geotextile and Sand Blanket under seawalls; 

3) Supply, Maintenance, Installation and Removal of Silt Curtain systems; 

4) Preliminary DCM trial panels; 

5) Supply and Installation of DCM panels within the Works Area; 

6) Coring, Sampling and Testing of DCM treated soils and reporting works; 

7) Environmental Monitoring and Protection Measures; 

8) Marine Mammal Monitoring and Dolphin Watching; and 

9) Cone Penetration Test and reporting.

The complexity of this project came from the immediate vicinity of the airport and the safety requirements that prohibited the use of equipment over 6m height.

16 CSM rigs were especially designed and built for low headroom conditions which achieved the works successfully, working 24 hours a day and 7 days in a week without ever interrupting the airport activity.

The typical panel size was 2.8 m x 1.2 m, average CSM toe level at -21.2mPD.

The average seabed level is -6mPD and headroom at +7mPD