Line 3 TBM drives complete for Riyadh Metro 16 Feb 2017

TBM excavations for the Orange Line 3 of the massive metro construction project for the city of Riyadh in Saudi Arabia have been completed by the ArRiyadh New Mobility (ANM) consortium led by Salini-Impregilo. In a report delivered to TunnelTalk from Underground Construction Manager Moriello Vincenzo, and TBM Operations Manager Bonfanti Omar, of Salini Impregilo for the ANM Consortium, the end of TBM operations for the Line was celebrated in the presence of Riyadh Governor HRH Prince Faisal bin Bandar Al Saud at the reception shaft on the far side of the Qasr Al Hoqm Downtown Station, one of three iconic landmark interchange stations on the extensive new metro system (Fig 1).

Celebrating a successful breakthrough

Final breakthrough for NFM Line 3 TBM

Commissioned by the ArRiyadh Development Authority (ADA), the Orange Line 3 of the six-line network is more than 40km long, with 5.7km aligned underground in single-tube, twin-track TBM drives and eight of its 22 stations also underground in open cut station boxes.

Moriello and Bonfanti confirmed that, after a peak performance of 20m/day and 600m/month, the single 10.16m diameter NFM TBM employed on the Line broke through to complete the last of its six drives. “From the launch shaft on the west end of the underground alignment, the TBM broke through into the open boxes of six of the open-cut stations and bored through the location of two others, with station box excavation beginning after the TBM drive-through,” explained Bonfanti.

TBM excavation on Orange Line 3 for the NFM EPBM was carried out in challenging geological conditions beneath an overburden of 25m to 35m, and in places below a high water table. The geology of Riyadh comprises a fractured sedimentary limestone layer sandwiched between two thick layers of breccia. Soil conditioning with foam, polymers and bentonite slurries have been required to manage high water pressures and tough terrain on the many TBM drives. Geology comprises limestone between two layers of breccia and a 5m layer of alluvium at the surface. The limestone, which can also contain solution or karstic features, has a reported UCS of up to 130MPa and an RQD of 90%.

On its journey for the ANM Consortium, the NFM TBM broke through into the massive open box excavation of the Qasr Al Hoqm Downtown interchange station where two of the new lines meet. The Orange Line 3 single tube, double track running tunnel is at the lower elevation with the single tube, double track running tunnel of the Blue Line 1 on the upper level. Accommodating the breakthrough, and launch again, of the TBMs working on the two lines and with simultaneous excavation of the station box resulted in a complex set of temporary works and intricate logistics within the massive box excavation.

Located near the Governor’s Palace in the heart of Riyadh, the iconic Downtown interchange station is designed by the Norwegian architect firm Snøhetta together with One Works and Crew and will be a landmark structure. Its entrance will be covered by a massive inverted cone made of stainless steel that will provide shade for passengers and channel sunlight into the underground station.

Fig 1. Network of the Riyadh Metro

Project progress

The Salini Impregilo-led (ANM) consortium is one of three consortia involved in construction of the $23 billion, six-line Riyadh Metro project. Awarded as five large design-build contract packages that include installation of M&E and supply of the rolling stock for each line, the full network is 176km long with about 49km and 35 of the total 85 stations aligned underground (Fig 1).

With group leader Salini-Impregilo (Italy), the ANM Consortium includes contractors Ansaldo (Italy) Larsen & Toubro (India), Nesma & Partners (Saudi Arabia); rolling stock suppliers Bombardier Transportation (UK and Canada), Ansaldobreda (Italy); and engineers Hyder Consulting (UK now part of the Arcadis Group of The Netherlands since 2014), Worley Parsons (USA) and IDOM (Spain). Construction of the 40km long Orange Line 3 with its 22 stations, including construction of Qasr Al Hoqm Downtown Station and the Western Metro interchange stations, plus M&E installation and supply of rolling stock, was valued at US$5.2 billion at time of award.

The BACS Consortium of Bechtel (USA leader), Vinci (France), Siemens (Germany), Almabani General Contractors (Saudi Arabia), Consolidated Contractors Company (Saudi Arabia), and engineers AECOM (USA) is completing the Blue Line 1 and the Red Line 2 and the Al-Olaya and King Abdullah Financial District interchange stations. The contract for the construction of the two lines, including installation of the M&E systems and supply of the rolling stock, is valued at more than US$9 billion: $6.561 billion for the Blue Line and $2.88 billion for the Red Line.

TBM excavation was through limestone and breccia

BACS procured four 10.25m diameter Herrenknecht multi-EPB and open mode TBMs to excavate more than 17.5km of single-tube, double-track tunnels on the 38km long Blue Line 1 with 22 stations The concrete segments for the Line 1 running tunnel drives were manufactured in a plant supplied by Herrenknecht Formwork.

The Red Line 2 is 25km long with 13 stations and 3 interchange stations and is aligned mostly at grade (15km) and elevated and with a 2km long section of NATM work for the transition into and out of the Red/Blue Line underground interchange station on King Abdullah Road (Fig 1).

The NATM work, designed for BACS by Gall Zeidler Consultants, was advanced using roadheaders through the limestone and breccia geology on a topheading of 10-11m wide x 5m high, bench and invert sequence. Following primary support of steel fibre shotcrete, a full hydrostatic waterproofing membrane system was installed and the tunnels of 1km either side of the underground station were lined with insitu concrete.

Line intersections at the Qasr Al Hoqm Downtown Station

Work on the Blue Line contract advances with installation of the emergency egress and ventilation shafts along the single-tube, double-track TBM running tunnel. The shafts are off-set to the axis of the running tunnels and are connected with NATM excavated adits. The rectangular shafts of 14m long x 9m wide and 25-30m deep will house both emergency stairways and elevators.

The FAST Consortium of FCC (Spain leader), Samsung (Korea), Alstom (France), Strukton (The Netherlands), Freyssinet (Saudi Arabia) and engineering companies Typsa (Spain) and Setec (France), is completing a total 64.6km of track and 25 stations for the 30km long Yellow Line 4, the 13km long Green Line 5 and the 30km long Violet or Purple Line 6 for a procurement value of about US$8 billion. Scope of the lines includes supply of a total 69 trains for the three lines.

Complex accommodation of TBM drives in the Qasr Al Hoqm Downtown Station box

The consortium deployed two 9.77m diameter Herrenknecht EPBMs to excavate the single-tube, double-track running tunnel for the entirely underground 13km-long Green Line 5. It was a Green Line TBM that recorded the first TBM breakthrough on the project, when the machine emerged into the 25m deep Salah-al-Din cut-and-cover station box in October 2015 to complete the first 1.2km of it total 5km long drive. The two machines were launched on the Green Line in April and June 2015 and after reaching progress rates of up to 260m/week, both machines reached their final breakthrough a year later in mid-2016.

The Yellow Line 4 and the Purple Line 6, both about 30km long, are mostly at-grade and elevated constructions.

The trains to be procured by each of the three consortia for the network are of the same uniform style and design with the trains for each line identified by their colour. The automatic driverless trains will run at a maximum speed of 100km/hr.

Construction of the extensive metro network, together with an equally extensive plan for metro bus services, will be vital for the city's future sustainability. The population of Riyadh is to increase from its current 6 million inhabitants to a projected 8 million by 2030. The new metro and bus systems will reduce traffic congestion and lower pollution. At present, about 2% of the city’s population uses public transportation.