Update on Metro Projects in Europe and Asia

Amberg Engineering has been involved in several metro projects globally and this paper highlights some of their interesting and special aspects. Unfortunately, the restriction on paper length means other projects such as metros in Porto, Barcelona, Lisbon and Quito cannot be included.

U5 BERLIN: CLOSING THE GAP BETWEEN ALEXANDERPLATZ AND BRANDENBURG GATE
Project overview

Due to the former division of Germany into West and East, there was a missing section on Berlin’s underground Line 5. But the recent construction of the required tunnels and stations between Alexanderplatz and Brandenburger Tor meant the new line was able to open in winter 2020.

The U5 project comprises the construction of three new underground stations and a connecting double-track tunnel which will be constructed using shield tunnelling. The project is sub-divided into two construction lots:

• Lot 1 comprises the GWA (Gleiswechselanlage), the MUI (Museum Island) station, the UDL (Unter den Linden) station, the connection to the Brandenburg Gate (BRT) station and the tunnels connecting these stations.
• Lot 2 includes the construction of the new Berlin City Hall station and the connection to the existing tunnel in the direction of Alexanderplatz.

Two parallel tunnel tubes with a length of around 2.2km each and an outside diameter of 6.5m are planned. The tunnels were constructed between 2013 and 2015 by a slurry tunnel boring machine (TBM) with a liquid-supported working face using the so-called shield boring method. Planning and undertaking the shield driving are particularly influenced by the undercutting of the bank walls of the River Spree and the Spreekanal; the impact on the ongoing construction of the New Berlin Palace; and the connection to the existing Brandenburger Tor station.

Three new railway stations will be constructed using both cut-and-cover, and top-down method with open deep excavations.

Rotes Rathaus station was built using the cover construction method in the immediate vicinity of the Berlin Rotes Rathaus. The station includes the connection to the tunnels already in operation on the existing U5 line. Near the station, a track-changing system was constructed in cut-and-cover and in some areas using top-down construction. This is the point at which signalling begins.

Museum Island station is located in the area of the Spreekanal (See figure 1) and is currently still under construction. The platform area of the station was constructed from the two station shafts under the protection of mining-style ground freezing.

The existing underground line U6 and the new U5 intersect at Unter den Linden station. For the construction of the crossing structure, the existing tunnels have to be demolished underground and rebuilt in order to create the connections.

Geology

The geology is characterised by thick sand and gravel deposits that serve as groundwater reservoirs. Locally, the sands are overlaid by organically interspersed sands or peat and mud in sometimes large thicknesses. The average groundwater level is around 3m below the ground surface.

Shield driving

With an inside diameter of 5.7m, the tunnel tubes are lined with reinforced concrete tubbings. A block tubbing ring with a thickness of 350mm is planned. The ring width is conical and averages 1,500mm. Segment joints are sealed with a closed elastomer frame embedded in a groove. The seal must be designed for a maximum water pressure of 3bar. A drilling grid is provided in the segments to allow the annular gap to be re-injected. The tunnel tubes are driven one after the other. It is planned to drive first the tunnel tube for track 1, then the tube for track 2.

MUSEUM ISLAND STATION

Museum Island station begins on the eastern bank of the Spreekanal and ends in the area of the command tower (figure 1).

The building consists of two shafts at the station’s ends with associated entrances and dividing levels, as well as railway riser pipes in between. Shafts will be built with a maximum depth of up to 43m using cover construction – the same way as the railway shafts are constructed. The bottom of the construction pits is secured by means of deep-lying DSV-blocks and bracing grids above them.

TBM tunnelling and most of the station excavation works have been completed, but the concrete works on this project are still ongoing.

Before the mechanised tunnel driving reaches the station area, the retaining walls of the subsequent shaft excavation pits are constructed using diaphragm wall construction. Within the excavation cross-section, GRP reinforcement will allow the shield-driving machine to punch through the excavation pit walls. In front of these, DSV bodies are produced on the ground side in order to achieve a defined sealing of the annular gap using grout which is injected between the lining segment and the diaphragm wall itself.

The platform hall is located in the area of the Spreekanal and is constructed under the protection of mining-style ground freezing. The minimum overlap between the frozen mass and the Spreekanal bed is around 4.5m. Creating the frozen mass is by means of horizontally-controlled boreholes with a maximum length of 105m. The frozen mass is then covered by the bed of the Spreekanal.

Due to the geometry of the station, it is necessary to drill the entire length of holes from one side. The planned static thickness of the frozen mass is 2m. Excavation of the platform hall will be achieved by a three-cell cross section consisting of one central and two side galleries.

The construction sequence envisages excavating the centre tunnel next to the side tunnels and then the side tunnels with a time lag in the mining dome driving with immediate bottom closure. The excavation is carried out by roadheader. The tunnels are secured with shotcrete. Excavating the side tunnels is carried out in the course of a widening of the cross-section in the area of the segment tubes. For this purpose, the segment tubes have to be broken off in partial areas and the excavation has to be secured. Installation of the reinforced inner lining in the centre tunnel takes place before the crosssection expansion in the side tunnels begin. Following the driving in the side tunnels, the reinforced inner shells are produced in the side tunnels and connected with the inner shell of the centre tunnel by friction. The thickness of the inner shells varies but is at least 450mm.

BRUSSELS METRO NORTH
Project overview

The new fully automated M3 metro line of Brussels will connect the northern suburbs directly with the city centre, passing through a densely-built area. The project includes the design and structural conception of seven new stations, a 4.5km-long single-tube tunnel with parallel tracks, a depot, a maintenance centre and all auxiliary infrastructure.

During the early project phases, it was decided to impose very strict requirements on the scheme in terms of safety, accessibility and reduction of disturbance (site and environmental impacts).

Requirements associated with the project imply the use of more complex techniques for the construction of the stations than those generally used. This high complexity is the result of integrating a series of very tight constraints including:

• Geological and hydrogeological conditions.
• High degree of urbanisation in the project area.
• Presence of listed buildings.
• Very limited space on the surface for construction sites.
• Geometrical and functional requirements of stations And
• Request to limit the number of expropriations.

Brief project description

The project is divided into three main civil engineering lots. Lot 1 comprises works for the crossing below the railway grid at Brussels North Station and the connection to the existing line.

Lot 2 includes the works for the maintenance centre and the depot. And Lot 3 – the biggest in terms of investment cost and complexity – comprises all civils works for constructing the tunnel, the seven stations and the connecting ramp to the maintenance centre.

Crossing the railway grid

To be able to connect the new bored tunnel with the underground structure of the existing line, a new tunnel section must be built below the 12 railways of Brussels North Station’s grid.

The embankments of Brussels North railways station were built hurriedly after the end of the Second World War using possibly all kinds of material, including metal objects and large objects. Here, extremely heterogeneous ground is anticipated. Due to the rushed build, the low overburden, combined with a risk of settlement of the existing tracks, it was decided to retrieve the TBM before passing under the tracks and to build the connection using a more conventional, method. The actual concept consists of building two longitudinal galleries from two shafts at each extremity of the crossing, and a multitude of transverse galleries linking the two main ones.

Temporary retaining walls are then executed with jet-grouting from the two main galleries. The whole complex of galleries is then filled with reinforced concrete to create a temporary structural roof slab.

After the construction of this temporary structure, the excavation underneath the actual structure can start. The soils are removed via the extremity shafts.

Tunnel

Due to the length of the planned tunnel and the high degree of urbanisation of the project area, it was decided that tunnelling would be carried out by a tunnel boring machine (TBM). The advantage of this technique is that it allows excavation and ground support with a very high advance rate (about 10m–15m/day, depending on conditions). Moreover, the process takes place with a very high degree of security and surface disruptions are minimised (compared to cut and cover).

Most of the tunnelling take place in the Bruxellien (coarse sand with local presence of harder concretions); Tielt (very fine silty to clayey sands with clay lenses) and Kortrijk formations (clays, sometimes silty or sandy). The groundwater table generally lies between 1m–10 m below ground level.

It was decided that a single tube configuration with parallel tracks is the optimal geometry for this project as it allows for reduced investment costs, reduced technical risks, increased operation flexibility and easier jobsite logistics. in the end, the inner diameter of the bored tunnel was fixed at 8.9m with an expected bore-diameter of 10m.

The biggest challenge for the tunnel’s construction is settlement control and mitigation. A detailed settlement analysis was performed and resulted in an extensive monitoring concept.

Stations

The station design integrates some very constraining factors, such as the high degree of urbanisation in the project area, the presence of listed buildings, and the requirement to limit the number of expropriations. As a result, the complexity of the design increased. Finally, after a thorough analysis of the site conditions, it was decided to realise sections of the platform zone – non-accessible from the surface – using a combination of microtunneling, ground freezing, timbered trenches and jet grouting to create a strong and sealed structure. Ground freezing is designed to be sufficiently strong and completely watertight to allow the safe construction of the platform zone structure. This method is chosen for four of the seven new stations on the M3 Line.

GRAND PARIS EXPRESS, LINE 17, LOT 3

The new metro Line 17 in Paris, France connects Bourget RER station and Le Mesnil-Amelot. This line is part of the new metro extension project of Grand Paris Express, which links Paris suburban areas and downtown. In 2030, this line will connect Le Bourget Airport and Charles de Gaulle Airport.

It comprises 19.5km of automatic metro line, 14km of which are in tunnel, five new stations and 14 complementary shafts. Lot 3 tunnel is a 6.5km-long, single tube tunnel extending from Tremblay-en-France to Le Mesnil-Amelot station. South to north it crosses all airport infrastructure of Charles de Gaulle Airport, including taxiways, runways and terminal buildings.

The main challenges of the design are:

• The very limited cover at the TBM launching point (only 3m);
• The geology, which contains traces of gypsum and in which there is a risk of encountering cavities in the airport area;
• Crossing Charles de Gaulle Airport, including two runways, taxiways, airport facilities (Sheraton hotel, luggage sorting facility, etc.) as well as a TGV and RER line. Here, settlement control and mitigation is the biggest challenge. The design in the airport zone includes 2D FEM settlement calculations; an extensive risk analysis with definition of mitigation measures; estimation of residual risk costs; and a high-level monitoring concept and coordination with ADP and SNCF (already in the early stages) to define tolerances and find the best solution in term of access to infrastructure, mitigation measures, etc.

AHMEDABAD METRO EAST-WEST CORRIDOR MEGA-PACKAGE UG2

Gujarat Metro Rail Corporation (GMRC – formerly known as Metro-Link Express for Gandhinagar and Ahmedabad (MEGA) Company) is implementing the Ahmedabad metro rail project in the state of Gujarat, India. Phase-I has a total length of 40.03km, of which around 6.5km is underground and the rest elevated. The project will connect the four corners of Ahmedabad City through two corridors and 32 stations.

The North-South corridor has a total length of 18.87km connecting APMC to Motera Stadium, comprising 15 stations and is completely elevated.

The East-West corridor has a total length of 21.16km connecting Thaltej Gam to Vastral Gam, with 17stations en-route. Of this, a roughly 6.5km stretch is underground with four underground stations; the remaining is elevated with 13 stations. The underground section is divided into two packages – UG1 & UG2 with two stations each.

The total cost of the entire Phase-1 metro rail project is estimated to be around US$1.4bn.

The architectural finishing and civil works of underground package UG-2 was awarded by GMRC to Larsen & Toubro (L&T) which appointed Amberg Engineering as detailed design consultant for the architectural and structural works. The scope of works in the project is as follows.

Project data

The project has a length of around 4.3km with two stations (170m and 270m length, built by top-down construction). Tunnel excavation is undertaken by two TBMs, each mining around 3.3km. At the west portal there is a ramp and cut-and-cover section of 280m length. The entire alignment of the UG2 package (described below) was awarded to L&T.

Bored tunnel

To construct the bored tunnels, two EPB TBMs have been deployed. Geological setup in the terrain mainly consists of filled-up soil underlying layers of silty sand (SM), clayey sand, and clayey soils of low-to-medium plasticity. The ground water table is low at around 12m-14m below EGL.

A temporary launch shaft was constructed at Kalupur to launch the two TBMs that operated at a maximum depth of around 24m-25m below ground level and have successfully passed below sensitive areas, such as the existing Indian Railways operational line, a few multi-storey buildings and many old and highly dilapidated buildings that made this section very challenging, given the stretch passes through the old city of Ahmedabad.

The entire tunneling on the project has now been completed, with TBM breakthroughs having occurred at Ghee Kanta station. Station structures are also now completed and finishing works are currently in progress.

Cross passages/emergency exits connecting the two tunnels are to be constructed using the New Austrian Tunnelling Method.

To understand ground behaviour, continuous ground monitoring is carried out using different instruments. Sensitive structures and critical buildings are fitted with a 24-hour monitoring system using data loggers.

Underground stations

Under package UG2, two underground stations are to be constructed – Ghee Kanta and Shahpur. Both are being constructed by top-down construction methodology comprising installation of diaphragm walls followed by sequential excavation and casting horizontal slabs. There are three slabs – roof, station concourse and base, with an island platform in the centre. Proper instrumentation and monitoring schemes based on settlement analysis and BDA is prepared and is being implemented on site to prevent any settlements in nearby structures.

Due to limited ground space availability at Ghee Kanta station, the station length has been restricted to 170m, with functional rooms being accommodated on the flared sides. It is a non-typical underground station: the large area in the centre of the station poses challenges for structural design, especially the construction sequence with regard to high-rise buildings with their basements in close proximity. The other station, Shahpur, is around 270m long. All underground structures are being designed with a 120-year service life.

One end of the Ghee Kanta station will be used as a receiving shaft for the TBMs launched from Kalupur launch shaft, while the other end will be used as a launching shaft for TBMs constructing the bored tunnel towards Shahpur station. The shaft areas have already been constructed and the works are now ongoing in the central part of Ghee Kanta station. The D-wall activity at Shahpur station is also nearing completion. Construction works on this project are still ongoing.

MUMBAI METRO LINE 3 – PACKAGE 7

Mumbai Metro Line 3 (MML3) is 33.5km long and the first underground metro line between Colaba–Bandra- SEEPZ, passing below Mumbai’s most congested and populated areas. Estimated cost is around US$4.3bn.

MML3 will have 26 underground stations and will connect Cuffe Parade in the south of the city to SEEPZ in the north central area. It will provide connectivity to important places, with minimal disturbance to road traffic and structures, and will minimise land acquisition costs compared to an elevated metro option.

Construction of MML3 is considered to be one of the most challenging metro projects to deliver, as it has to pass below congested areas, old buildings, multi-storey buildings, the Mithi River, overground metro/railways, airport, flyovers, water bodies, heritage structures and many other important infrastructures.

The project is being delivered by Mumbai Metro Rail Corporation (MMRC). Total works have been split into seven construction packages. The Larsen and Toubro STEC Joint Venture – which was awarded construction of MML3-Package 7 – appointed the Amberg Engineering/STUP Consultant Joint Venture as detailed design consultant to deliver the design work.

MML3-Package 7 comprises the construction of three underground stations, namely Marol Nata Station, MIDC Station and SEEPZ Station; a 7.1km TBM tunnel;14 bored tunnel cross-passages; and a 200m cut-and-cover tunnel and ramp section to enter into the depot.

Bored tunnel

To construct the bored tunnels, two EPB and one dual-mode TBM were deployed. Geology mainly comprises top residual soils underlain by weathered rock and bedrock. These machines have bored mainly in rocky strata comprising mixed ground conditions with breccia, basalt and volcanic tuffs of different weathering grades, and a high groundwater table.

TBMs have successfully passed below sensitive structures, such as Mumbai Metro Line 1 (elevated metro line); Mariott Hotel (5.7m clear cover); three Sahar Airport flyovers (piles in 4m proximity); JVLR link road (pile foundation with 2.5m lateral cover), and numerous dilapidated buildings.

High water ingress was reported at several locations and treated with grouting to enable safe tunnelling. Of the 7.1km, the machines have bored more than 6km without any major issues. So far, the performance of the EPBM machines is better than the dual-mode TBMs.

Underground stations

Under Package 7, three underground stations are constructed – Marol Naka, MIDC and SEEPZ. All three were constructed using bottom-up construction methodology. This saw excavation of the station box first and subsequent construction of the station building. Secant piling was adopted for retaining the top residual soils and weathered rock, whereas rock bolting and shotcreting with wire mesh were used as primary support in the rocky conditions.

Due to limited ground space availability at Marol Naka, station platforms are planned to be constructed under 250m long tunnels running parallel on either side of the station box. Platform tunnels are connected to the station box by 16 connecting tunnels. Of these, 12 will be used for public access and four will be used for other services. Below is a diagram of Marol Naka station box with platform and connecting tunnels.

Most of the temporary work and excavation of station boxes has been completed. Construction of the station wall and slabs is in progress at all three stations. At Marol Naka, the bored tunnel is constructed first and is now enlarged into a 12m-wide platform tunnel using NATM. Pre-consolidation grouting is carried out to consolidate and restrict water ingress into excavation faces. Platform tunnels are supported using shotcrete, wire mesh, systemic bolting and lattice girders as primary support. These tunnels will be supported with RCC lining and designed for a project life of 120 years.

Continuous ground monitoring has been carried out using different instruments. Sensitive structures such as metro piers and critical buildings have been fitted with 24-hour monitoring using data loggers. Considering the urban environment, blasting is avoided for enlargement of the TBM tunnels.

Construction work on this project is still ongoing.

STOCKHOLM METRO, TUNNELBANA, ODENPLAN – ARENASTADEN – HAGASTADEN
Project overview

This 4km-long project comprises:

• 2km two-track tunnel
• 2km one-track tunnel
• Two intersections, three escape routes
• Two access galleries, two ventilation shafts
• Three stations, two in rock formations, one in cut-and- cover
• Conventional drill and blast heading, cover ranging between 3m–40m
• Geology is characterised by competent crystalline formations of gneiss and granite, and a covering layer of clay moraine and filling grounds. The following aspects highlight the special aspects of the project:
• Tunnelling in an urban area with low cover and below buildings of sensitive settlement;
• Complex logistics for site installation with limited space and access
• Difficult connection to existing network and need to be planned and completed over a few night shifts and two summer breaks of a few weeks duration.
• Several existing facilities to be crossed with low cover, without incurring any damage or operational restrictions.

BIM and 3D geotechnical models

The entire project design was achieved using BIM with co-ordination and clash-control based on results of 3D-model calculations, and also the determination of quantities by modelling. Due to various changes and a bulk quantity of technical disciplines working in parallel, the modelling task was the most time-consuming part.

The stations were analysed with a 3D numerical analysis, as those areas have a complex geometry with big spans, several weakness zones and occasionally, low overburden. The acquisition of the Rhino Plugin Griddle, developed by the Itasca group, allowed us to perform seamless geometry transfer from Rhino to FLAC3D.

FLACD as a routine was generated to show the influence of the weakness zones within the analysis. The routine conducted two separate numerical analysis runs. One contains no weakness zones and is used as a reference case; and the other is modelled with them, allowing quantification of the influence. The quantification is performed by checking the difference in the absolute displacement magnitude and by examining the ratio of the displacements in both cases. The methodology and all work to analyse models, compile results and associated reports were developed by Amberg.

Less complex areas were analysed using 2D numerical analysis in Phase 2, with explicit joint network modelling.

The quantities were estimated in a 3D model. The volumes were used to calculate the excavation volume and blasting efforts for each round-length class. The surfaces were used to calculate the quantities of shotcrete, bolts, grouting, drainage mats, etc.

CONCLUSION

Highlights and details have been described for each of the above projects. The interesting topics range from soft soil or mixed ground conditions for the TBM drives; construction of an underground station by means of ground freezing; passing under existing runways and airport buildings; passing under an existing railway station; undertaking the entire project using BIM; and construction in densely populated parts of mega-cities such as Mumbai.

All these hurdles must be faced and overcome when building metro projects globally. The photographs which have been received of the finished or ongoing construction works prove the correct work was undertaken by the design teams.

We would like to thank all our clients and partners for this effective and successful cooperation.