Diaphragm wall quays for Myanmar Mega-Port (Dawei Seaport)



Christopher Carr and Maki Onodera, Halcrow (Thailand) Ltd., Bangkok, Thailand



The Dawei Sea Port (DSP) is the centerpiece of a multibillion dollar infrastructure and industrial development project in Myanmar. Major elements of the project include a new port and industrial zone located in southern Myanmar (near the town of Dawei) and highway and rail systems connecting the port to central Thailand, to provide access to transportation infrastructure to South China and other regions within Southeast Asia. The developer will be the Dawei Development Company Limited (DDC) and the general contractor will be the Italian-Thai Development Public Company Limited (ITD). The DDC was established by ITD after being awarded a 75-year concession by the Myanmar government to develop the Dawei Development Project, an ambitious project comprising an industrial estate covering nearly 204 square kilometers, oil and gas facilities, a deep sea port, power plants, steel mill, shipyard, a new township, and a transborder road/rail/power link with neighboring Thailand.

The port development will ultimately include 55 berths, including terminals for containers, general cargo, liquid cargo, LNG, coal and iron ore. In 2011 the Halcrow-Aurecon Design Consortium (HA) was awarded a contract by ITD for master planning, data acquisition, feasibility and optimization studies, and the detailed design of the port. This article provides a brief overview of the DSP project and a detailed discussion of the unique quay wall system that will be used, with concrete diaphragm walls (slurry walls).

Port layout

The layout of the port features a breakwater-protected Outer Harbor and an L-shaped Inner Harbor. The Outer Harbor will be used for berths with open pile supported structures, including the liquid and Dry Bulk terminals, the LNG terminal, and the tug base. The Inner Harbor will be used for the container and general cargo terminals, and will have closed quays constructed using diaphragm walls. The Inner Harbor will have a depth of 16meters while the Outer Harbor will have a depth ranging from 14meters to 20meters.

The first phase of construction includes facilities for the Outer Harbor and the initial portion of the Inner Harbor, together with dredging, reclamation, and shore protection works, see figure 4. The breakwater system has an overall length of approximately five kilometers and will be constructed with dynamically stable rock breakwaters ( ‘berm breakwaters’), using widely graded armor stone produced from a quarry located adjacent to the site. Extensive 3D physical model tests were performed in order to optimize the port layout and breakwater design, at the Canadian Hydraulics Centre (CHC) and the Council for Scientific and Industrial Research (CSIR) in South Africa. Comprehensive coastal numerical modeling studies were also performed in support of the design work and to assess environmental impacts. Modeling issues of special concern include the potential for deep scour holes near the tip of the breakwaters, and the potential for excessive wave agitation at the container terminal caused by the penetration of long period (infra-gravity) waves, due to prolonged periods of high swells during the Southwest monsoon.

Diaphragm wall quays

Conceptual designs and comparative construction cost estimates were developed for a number of alternative quay wall design concepts, for both in-the-dry and in-the-wet scenarios for the basin excavation and quay wall installation. Anchored wall options included steel sheet pile walls with king piles, and diaphragm walls with single and multiple rows of tiebacks. Gravity wall options included steel sheet pile cells, concrete block walls, concrete caissons, and slip-formed concrete gravity walls. Platform quays were also considered, including various types of pile supported platforms with revetments.

The selected concept uses a concrete diaphragm wall with a single row of tie rods. This scheme was selected because it offers relatively low lifecycle costs, and provides important advantages from both design and construction standpoints. The diaphragm wall system consists of 1.5 meters thick wall panels with T-section panels at the locations of the fenders and bollards, which are spaced at 12.5 meters. The wall superstructure, above Low Astronomical Tide (LAT), features a precast concrete fascia wall system that is connected with cast-in-place elements. The tieback system consists of 110 millimeter diameter x 46 meter long tie rods, spaced at approximately 2.1meters, connected to a precast concrete deadman. Bored concrete piles are used for the foundation of crane beams at the container quays.

Typical cross-sections of the quay wall are shown on Figures 5 and 6.

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