Fabric producer: TenCate Geosynthetics Asia
Fabric supplier: TenCate Geosynthetics
Engineer: Oriental Consultants Co., Ltd. and Japan Bridge & Structure Institute, Inc.
Design: Nippon Koei Co., Ltd.
Project manager: Sumitomo – Mitsui Construction Co., Ltd.
Installation: Truong Son Construction Co., Ltd.
Location: Haiphong, Vietnam
Please describe the project specifications.
27 km of geotextile tubes were installed to reclaim the 4.1 km by 26m wide works platforms and construct the 600,000 m3 dredged sediment containment facility for construction of Lach Huyen Bridge. The proposed 5.4 km bridge which accommodates a four lane highway spans across the combined estuary of Bach Dang River and Cam River. About 23 km of geotextile tubes were used for the construction of the reclamation dykes. The tubes were segmentally stacked up to 5 layers high for the construction of the works platforms. The tubes used for the construction of the reclamation bund comprised of circumferences of 4.6, 6, 7.5 and 9.5 m, with typical lengths 50 m. The works platform together with the tubes will eventually be embedded within a future land reclamation that will enlarge the Dinh Vu Development Area to approximately double its current size. A portion of 1.3 km of the bridge was constructed by the offshore method using work barges. A 1 km long channel along the alignment of the bridge was dredged to increase water depth sufficiently to allow the work barges to operate without any low tide interruptions. A dredged spoil containment facility was required to contain the dredged material. Geotextile tubes were also used to construct the perimeter dyke of the containment facility. It was constructed using geotextile tubes with standard length of 15 m and circumference of 9.5 m. The bottom level consists of two units placed side by side and a top unit placed centrally above that.
What was the purpose of this project? What did the client request?
A construction methodology that would overcome very soft ground conditions, withstand typhoons and avoid disruptions to construction activities (by the large daily tidal ranges) so the bridge could be completed within the targeted project duration. To allow bridge construction activities to be carried out on dry land expediently, two construction works platforms were reclaimed along the alignment of the bridge. The works platforms with approximate width of 26 m and 4.1 km in total length were built to RL 2.55 m; above the highest tide levels and out of reach of storm surges and impacting waves. Rock is commonly used to construct containment dykes for reclamation works but is difficult to source and expensive in the area. Sand is readily available and dredged from the channels nearby for the reclamation of the works platform. Dredging is carried out using a suction dredger. The dredged sand is stored in a temporary storage yard for use as reclamation fill to construct the works platforms. Since sand is readily available the geotextile tube solution became an economical alternative to the rock fill solution. It was very convenient to tap into the hydraulic delivery of the sand for the installation of the geotextile tubes. If the rock fill solution was adopted instead, not only the rocks have to be purchased at high cost and transported over a long haulage distance, the placement of the rock fill would have been very challenging in these tidal and very soft seabed conditions.
What is unique or complex about the project?
Bridge construction works require heavy machinery for installation of foundation piles, construction of bridge piers and launching of bridge sections. Very soft ground and adverse tidal conditions are the two main construction challenges. The very soft ground conditions create difficulty for machinery to work on. A significant portion of the bridge alignment is under shallow water either part of the day or all the time. Except for the narrow navigation channel, there is insufficient water depth available for marine barges and equipment to carry out continuous construction works.
What were the results of the project?
The geotextile tube solution allowed the use of locally available sand to replace rock for the reclamation and containment dyke construction works. This geotextile tube solution helped reduce construction costs and time. The Lach Huyen Bridge will be the longest sea crossing bridge in Vietnam, providing a shortened link between Haiphong and Lach Huyen Port, (currently under construction). The geotextile tube solution also survived a direct hit by Typhoon Kalmaegi during construction in September 2014.
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