Vol 20 No 6 (06-2011)
Site Formation and Foundation Works for Property Development at TW7 Tsuen Wan West Station (Contract TWTL No. 403)


Background

The MTR Corporation Limited (MTRCL) has planned three property projects, namely TW5 which is located above Tsuen Wan West Station; TW6 near Tsuen Wan Park and TW7 near Waterside Plaza at the West Rail Tsuen Wan West Station. Among the three, TW7 is the initial project to be constructed. The project, which is developed jointly by the MTRCL and Queensway Investments, a subsidiary of Cheung Kong (Holdings) Limited, occupies 2.37 ha area and is located at the southeast of Tsuen Wan West Station, bounds by Tsuen Wan Road on the northeast and Wing Shun Street on the south. Seven towers are to be built upon the completion of the foundation work. It is expected that
1,740 residential units will be provided and the gross floor area occupies about 113,064 sq. m.

About the Project

Kin Wing Foundation Limited (Kin Wing) was awarded as the main contractor of the site formation and foundation works. The construction work of about 18 months has commenced in September 2009 and was completed in April 2011.

Scope of the work is as follows:

1. Design and construct the bored piles foundation for seven towers.
2. Design and construct the pile caps for seven towers ( Post-tensioning for three towers)
3. Design and construct the excavation and lateral support (ELS) works
4. Design and construct the site formation works (including retaining wall, soldier pile wall, drainage system and rock slope formation)

Construction of Piles

The Contractor needed to construct 82 large diameter bored piles in which the deepest ones are 35m underground. These piles, with diameters range from 1800mm to 3200mm, have included 45 piles of 32m diameter which are the largest bored piles used in the MTRC property development projects up to present. During the peak period of the works, eight reverse circulation drills were used simultaneously to speed up the progress.

Piles Details

- 45 nos. of 3200mm-dia bored piles
- 4 nos. of 2200mm-dia bored piles
- 2 nos. of 1500mm-dia bored piles
- 8 nos. of 3000mm-dia bored piles
- 20 nos. of 2750mm-dia bored piles
- 3 nos. of 1800mm-dia bored piles
- Total 82 nos. of bored piles

Construction of
Pile Caps

Since three out of the seven towers are situated above the two West Rail train tunnels and the alignment of the tunnel passes right through the middle of the site, there is limitation when choosing the installation spots. As a result, the piles are installed at two sides of the site to avoid the tunnel area but it makes the distance between two opposite piles a lengthy 32m. In other words, a 32 meter-span pile cap has to be built. This also implies that traditional way of constructing pile cap is unfeasible in that area. Finally, post-tensioning method was adopted to build this large span pile cap. This is also the first time such method is adopted in the MTRCL's pile cap construction work.

Environmentally-friendly

Environmentally-friendly construction has always been developers and contractors' concern, thus it has always been taken into consideration that whether building materials are reusable or not. Firstly, materials excavated from site formation are sorted. Suitable rock materials are chosen to be reused in other construction projects while steel and metal are collected to be recycled. Treated waste water of the works is utilized in sprinkling the road surface and wheel-washing. The tailor-made noise and dust barriers equipped with sprinkler head are invented to mitigate noise and dust generated from excavation. To satisfy the concept of "Green Construction", solar traffic warning lamps are also adopted in the site.

Industrial Safety

The contractor puts industrial safety in first priority that every access in the site has already been smoothened or covered by anti-slip planks. In an attempt to strengthen workers' consciousness in construction safety, a reminding assembly was held for workers every morning; the contractor and sub-contractors meet regularly in striking to improve construction procedures with advanced safety precautions. "Zero accident and Zero Non-compliance" has achieved with all the above efforts throughout the construction period.

Challenges

In the project, pile caps with the largest span width up to 32m are built above the railways. Taking into consideration also the utter importance to assure the safety for the operation of the railway line, computerized automatic deformation monitoring system has been installed into railway tunnels for real-time 24-hour tight supervision.

Besides, the "post-tensioning" method in building pile caps requires at least 3m space in placing bulky equipment. Therefore, additional peripheral design and construction has to be carried out for excavation and lateral support (ELS) works.

Conclusion

With the completion of the site formation and foundation works for property development at TW7, residential projects will hence be commenced on site while approximately seven building blocks will be constructed, providing almost 1740 residential units.


Courtesy acknowledgement :
MTR Corporation Limited
Cheung Kong (Holdings) Limited
Kin Wing Foundations Limited
for providing the above information and photos