Record circle line: highlights of the BCL construction

A month ago, the Big Circle Line (BCL) construction has been completed. On March 1, the last nine stations of the northeastern, eastern and southern sections were opened, and full-fledged train traffic was launched along the entire circle line at the same time.

The BCL became the longest circular metro line in the world. It is a unique transport facility: more than 70 kilometers and 31 stations. The BCL connects all radial metro lines, the platforms of the Moscow Central Circle and the Moscow Central Diameters.

At full tilt

It took only ten years to construct the Big Circle Line, and the stations were built in two or three years. Given the scale and complexity of the work, meeting such a tight deadline was a real feat for designers, architects, engineers and builders. About 20,000 specialists participated in this megaproject; the work went on around the clock on a three-shift basis. During the peak period of the BCL construction, over 11,000 people worked at the sites per day.

Most of the BCL stations are shallow stations built using the cut-and-cover method. Deep stations were built using the bored tunnel method in highly congested areas with a large number of utilities, the removal of which is long and expensive. The BCL has three such stations: Savyolovskaya, Rizhskaya and Maryina Roscha.

Giant digging machines

In the 1930 s, the tunnels were built almost by hand, whereas today the builders have the cutting-edge equipment, including tunnel-boring machines (TBM). The BCL tunneling work was carried out using six-meter shields and 10-meter giants designed for double-track tunnels.

A tunneling control center was established to facilitate the BCL construction. It helped specialists identify and solve any problems: the tunneling progress information was received in real time to quickly adapt the actions of the tunnel boring machine crews.

33 shields were used to construct the circle line. In 2020, Moscow set a world record: the metro was simultaneously built by 23 tunnel-boring machines, most of which were used to construct the future BCL. In addition, when constructing a double-track tunnel in the western section, the Liliya shield crew set a record: 500 linear meters per month.

Advanced construction

Since the Big Circle Line route passes through highly congested areas, it includes many underground utilities. During construction, specialists used an underground monitoring system. It helped find out how the work would affect the surrounding buildings, and where the foundations of structures located above the metro tunnels under construction should be strengthened.

When constructing the BCL western section (Terekhovo, Kuntsevskaya and Davydkovo stations), the designers used elements of information modeling technologies for the first time in the history of the Moscow metro construction. This step enabled them to connect the engineering systems of the station with each other, minimizing collisions during construction. When constructing the BCL eastern section (Klenovy Bulvar, Nagatinsky Zaton, Pechatniki, Tekstilshchiki and three tunnel structures), the designers developed a single 3D model. The use of information modeling elements and 3D models streamlined many workflows, improved design solutions and reduced the construction time.

Water inflow, quicksand and other enemies of tunnelers

However, utilities were not the only problem of the BCL builders. Almost two kilometers of tunnels passed under large bodies of water such as the Moskva River, Yauza and Nagatinsky Backwater. The longest track among the BCL underwater tunnels is located on the eastern section between Nagatinsky Zaton and Klenovy Bulvar stations covering an area of 550 meters.

Underwater tunneling is a technically challenging process. Workers cannot dig a trench to repair the shield and to replace the cutting tool of the tunnel-boring machine on the extended sections under water bodies. This requires caisson work using special structures called pressurized caissons.

In addition, Moscow soil holds too much water, it accumulates in caverns. The water is retained in loamy and sandy areas. To control moisture, specialists used equipment to lower the water level. Quicksands, masses of fine sand and silt mixed with clay and saturated with water, like a sponge, are also an obstacle for tunnelers. Such complex areas were frozen using liquid nitrogen or refrigeration units.

Unique conveyor and vibration damping plates

To build the metro line in challenging areas, experts resorted to other innovations. For example, a round 40-meter shield chamber non-typical for the Moscow metro was built for tunneling work in the Rizhskaya-Sokolniki section. A unique vertical conveyor was designed specifically for this facility. The use of a conveyor belt allowed specialists to automate the production of up to 600 tons of soil per day and significantly speed up tunneling.

In the eastern part of the BCL, between the Tekstilshchiki and Pechatniki stations, builders used an extraordinary technology for lowering a 10-meter shield. They used a portal system capable of lifting loads weighing up to 1,200 tons. With its help, the shield elements assembled on the surface, including the head part weighing 870 tons, were moved to the shield chamber. This decision ensured reduced installation time of the tunnel boring machines and simultaneously work at other sites. The shield is commonly lowered in parts and assembled underground.

Under the Moscow International Business Center, trains travel along the uniquely designed tracks with vibration-damping plates, which reduce the load on the structures of high-rise buildings.

The longest escalator and new generation materials

While constructing the Big Circle Line, another record was set: the longest escalator in Moscow appeared at Maryina Roscha station. It is 130 meters long. It is four meters longer than the previous record holder, the escalator Park Pobedy station.

All the BCL stations have an individual architectural design. For example, Elektrozavodskaya is decorated with a large panel, 163 meters long. Battle of Heroes by Alexander Rukavishnikov displays a collective image of the defender of Ancient Rus. ’

The design of six stations, including Mnevniki, Terekhovo, Maryina Roscha, Rizhskaya, Nagatinsky Zaton and Klenovy Bulvar) was selected as part of international architectural competitions. Engineered quartz, a durable and wear-resistant man-made material, was used at Vorontsovskaya and Novatorskaya stations for the first time in the history of the metro. It allows specialists to use a wide range of colors when finishing. Fiberglass was used at Terekhovo station. It is a light and durable material of the new generation.

About 10 types of natural stone were used to finish the BCL stations. Three types of Sayan marble, Polotsk marble and Baltic granite were used when facing the walls. Siberian, Shimanovsky and Kambulatovsky granite were selected as the flooring material. The walls and floors of some stations are decorated with gabbro and labradorite.

In addition to unique materials, the BCL stations feature unique finishing technologies. When decorating Nagatinskiy Zaton’s lobby, specialists used a rare stone intarsia technique: fish images were made in a marble support with recesses filled with paint; the platform area features mosaic panels with giant reservoir inhabitants. Terekhovo station was decorated with the silhouettes of human figures, which were applied to the columns using digital concrete printing.