Gulf Construction Online - Metro set for historic run

Dubai Review

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Metro set for historic run

01 April 2009

THE date 09/09/09 is set to be a momentous one in the Gulf’s annals: it is the day when the region’s first metro – the Dubai Metro – begins operations. Globally, the ambitious project claims yet another distinction: it is the world’s longest fully automated rail network as one unit.

The $6.3 billion Dubai Metro has the potential to transform the behavioural pattern and lifestyle of many people in Dubai, while furthering the Roads and Transport Authority’s (RTA) goal of providing safe and smooth transport. It has been envisaged to include a total of four lines – the Red and Green lines which are currently under construction and the proposed Purple and Blue lines.
The Dubai Metro has a 75 km-long track that encompasses elevated, at-grade and underground sectors with 47 uniquely-designed stations. These include 10 underground stations strategically positioned in central Dubai, and 37 elevated stations.
The first phase of Dubai Metro, which is the Red Line, is scheduled to commence operations on September 9, while the second phase – the Green Line – is set for launch in March 2010. Some 23,000 and 18,000 passengers per direction per hour are expected to use the Red Line and Green Line, respectively.
The 52-km Red Line will have 25 elevated stations and four underground stations (Port Sayed, BurJuman, Union Square and Al Rigga) while the 23-km Green Line will have 12 elevated stations and eight underground stations (two being interchanged with the Red Line).
The overground section has a total length of 47.4 km, from Rashidiya to Jebel Ali for the Red Line and covering 15 km from Al Qusais 2 to Creek for the Green Line.
Speaking exclusively to Gulf Construction on the current status of the project, Adnan Al Hammadi, director, rail projects construction at the RTA, says: “Around 90 per cent of the work on the Red Line and 55 per cent of the Green Line has been completed.”
The tunnelling works on both the Red and Green lines was completed last December and the tunnel boring machines (TBMs) have been dismantled, he says.
About 90 per cent of the viaduct work on the Red Line and about 92 per cent on the Green Line has been completed.
The Dubai Metro project includes 60 km of viaducts – 45 km for the Red Line and 15 km for the Green Line. The viaducts comprise a series of precast post-tensioned concrete arches – supported by piers – that carry the railway track. The U-shaped section of the viaduct maintains the vertical rail alignment as low as possible to effectively contain the noise radiating from the track level in order to minimise the impact on the surrounding environment.
The viaduct decks, which have spans ranging from 20 m to 72 m, are erected using launching girders. The segments are pre-cast in steel moulds, cured and stocked in Jebel Ali Casting Yard.
“At peak time, a total of 40 segments per day will be produced using 20 types of moulds,” Al Hammadi points out.
The viaducts also carry the station concourse and platforms, effectively supporting most of the stations and the railway.
Turning to the work on the metro stations, Al Hammadi says: “Work is ongoing on all the 47 stations including the two stations at the airport terminals 1 and 3.
“On the Red Line, the first layer of cladding works is complete on the Rashidiya, Financial City, Business Bay, Al Quoz, Marina, Jumeirah Lake Towers and Al Karama stations. Glazing work is complete at Jebel Ali Industrial Area, while at Al Garhoud station the raised flooring is finished. At the Mall of the Emirates, the automatic fare collection gate room frame and raised floor is ready as is the first layer of cladding works.
“On the Green Line, the roof cladding for all overground stations is complete while other civil works are in progress.”

Metro stations
The metro stations reflect the modern metropolis of Dubai with key objectives of the design being safety and security of the public, minimising travel distances and entrances coordinated with pedestrian routes to other means of public transport.
Once inside, passengers will experience cool and calming interiors through a design based on the four elements of water, air, earth and fire. Throughout the stations, clear signage, lifts and facilities for passengers with special needs ensure a safe and quick journey on the Dubai Metro.
“The Rail Agency meets the international standards set by many developed countries since it benchmarks itself to countries like Hong Kong and Singapore in terms of special needs facilities,” Al Hammadi says.
The distinctive curved roofs of the elevated stations are the signature of the new metro, with their large shell-shaped roof evoking the heritage of pearl diving. This theme is extended to the underground stations and the smaller shell roofs of the stations, he says.
The overground stations are generally elliptical in shape. Elaborating on the design of these stations, Al Hammadi says: “The principal design philosophy is to have a station wrapped around the track but isolated from it in terms of vibration and deflection, with the exception of platform which is an integral part of it.”
There are three types of overground stations, one which is at-grade station and the second, which is elevated such that the whole station structure is carried on a raised concourse floor supported by main viaduct columns situated along the medians between highways. Type Three is a special station with a larger footprint to accommodate additional rail tracks.
Structurally, the station comprises structural steel main transverse arches with built-up box sections spaced at 6-m centres and with longitudinal rectangular hollow section ties spaced at 2.5 m centres. The stability of the structure depends on the portal action of the transverse arches and cross-bracing tensioned bars in the longitudinal direction.
The roof of the steel structure is partially clad with a metal decking with rear-ventilated cladding panels and glazing to meet the architectural and best international technical requirement in terms of watertightness, acoustics and insulation.
Lighting: Lighting of the stations will play a vital role in providing easy circulation of passengers, while creating a safe and secure atmosphere. Even ambient light levels will be maintained throughout the stations, while a higher level of lighting and special effects is being provided to meet specific requirements and enhance safety.
The lighting strategy includes:
• Day-lighting, which will be provided mainly in elevated stations through the glass walls and the scattered openings in the roof, as well as at one of the underground stations (Al Rigga Station) through providing special skylight features;
• Linear boom lighting;
• Special highlights; and
• Dynamic feature lighting.
Landscaping: All stations have been designed to fit in with the urban environment in which they are located and hence the landscape design around each station is an important element.
Designed to complement the stations and entrances, the landscaping helps direct passengers into the entrances and provides shading to open areas. The planting will include grass, shrubs and trees. Plants will be chosen based on their suitability to Dubai’s climatic conditions and require minimum maintenance and will be supported by an automatic irrigation system.
Landscaping under the viaduct is limited to hard landscaping – that is, lighting/reconstituted stone and concrete paving slabs etc – while soft and hard landscaping will be limited to 10 m in the vicinity of each station.

Construction technique
Commenting on the technique used to construct the elevated sections, Al Hammadi says: “The launching girder method – commonly used in erecting segmental bridges and railways – is utilised to lift and position the viaduct segments for the elevated sections. The 10 launching girders deployed on this project are strategically placed at various locations and moved upon completion of the planned number of spans.
He continues: “The girders provide a fast-track installation process which enables a complete viaduct span to be erected in about two days. Concrete segments are pre-cast and transported to the various sites. A total of 12,730 precast concrete segments will be used for the Red Line, each weighing about 50 tonnes. The girders are positioned over a span to be constructed and supported by a tower connected to the end of the deck and the next pier.
“Standard beams are used for positioning single or double-track segments with lengths varying between 20 and 44 m, while special girders are used for single-track stations (Nakheel and Rashidiya).”
The underground stations were constructed using the “top-down” method, which entails construction of concrete diaphragm walls – also known as retaining walls – as the first step of construction, followed by excavation just below the roof slab level of the underground structure, with the diaphragm walls and bars supporting the soil at the sides.
The roof slab is then constructed, providing a support across the excavation. Access openings on the roof slab are provided to proceed downwards to the base slab level of the structure.
The next level of slab is constructed, and this process continues downwards until the base slab is completed. Upon completion of the base slab, the side walls are constructed and the intermediate steel structures are progressively removed. The access openings on the roof slab are then sealed and the ground is subsequently back-filled and reinstated.
The project introduced the use of a TBM in Dubai. The TBMs were used to dig tunnels over 8.5 km long – two were used for the construction of both the Red Line and Green Line, while a third was used solely for the Green Line.
The TBMs employed in this project are of the earth pressure balanced (EPB) type with confined pressurised excavation chamber. They are equipped with cutting heads including special blades for cutting weak rock as well as a foam injector at the excavation face for improving the fluidity of the excavated spoil, thus decreasing the damage to the cutting heads, according to Al Hammadi.

Main power stations
The project has three main power stations (MPS): MPS 1 and MPS 3 feed the entire Red and Green lines and the entire power rail and the stations, while MPS 2 – located at Union Square – acts as a standby station should there be an electrical fault at either stations, according to Al Hammadi.
MPS 1 and 2 have been completed, energised and handed over by the contractor to RTA and Dubai Electricity and Water Authority (Dewa), while MPS3 is now undergoing equipment testing before its energisation, he says.

On the track
Trial operation of Dubai Metro was launched last September by Sheikh Mohammed bin Rashid Al Maktoum, Vice-President and Prime Minister of the UAE and Ruler of Dubai. The train ran for 11 km between Jebel Ali Station and Ibn Battuta Mall Station.
According to the scheduled timelines, the longest train run was successfully conducted from Jebel Ali to Emirates station, covering approximately 49 out of 53 km on the Red Line at a speed of 50 kph, says Al Hammadi.
He continues: “Currently 44 trains have arrived at the depot at Jebel Ali and the post-delivery visual inspection on 42 trains has been completed. Four trains have been delivered out of the planned 17 for the Green Line. The Red Line track and power rail installation is complete. The routine dynamic tests are complete on 25 trains. Around 25 per cent of the installation on the operational control system is complete.
“The test track has been extended to Marina station and static tests have been started at Jebel Ali Industrial, Jumeirah Lake Towers and Marina stations.”
Among other works, the platform screen doors (PSDs) for 10 stations have been installed.
With the project now nearing the much awaited-date, what else is left to be done?
“There are a few activities left to be done on the metro, which the entire project team is fully committed to complete on time,” Al Hammadi comments. “The main activities for the Red Line include the completion of the fitting-out works and cladding installation to the stations and entrance pods, completion of the viaduct emergency evacuation staircases, completion of the access roads to the stations, fitting-out and cladding of the car-parks and depots, and testing and commissioning of the sophisticated railway systems. Most, if not all, of these activities have already started and every effort is being exerted by the project workforce to complete these as quickly as possible.”

Proposed lines
Meanwhile, for the Purple and Blue lines, the RTA has commenced a study to update and develop the planned metro and tram lines with the aim of developing an integrated rail transit masterplan.
“A consultant has been on board since February to study and determine the rail lines that are required to meet the future demand in Dubai up to the year 2030,” Al Hammadi indicates. “The results of the study will be revealed in December and depending on the economic situation, future extensions of the rail would be implemented as necessary.
“The study will also define appropriate alignment corridors for the proposed lines, the required locations for stations and depots, type of technology for each line, overall rail network requirements, identify the best integration locations with existing rail and other modes of transport, including private developers transit systems and provide a capital cost estimate and implementation programme for the proposed new lines,” he concludes.