Washout in the Saint Petersburg Metro — an accident on the section between the "Lesnaya" and "Ploshchad Muzhestva" stations, which occurred as a result of the destructive impact of quicksand on the tunnels. The running tunnels had critically subsided, so they had to be closed and flooded. Passenger traffic on the section was suspended from December 2, 1995, until June 25, 2004 — the moment of commissioning after the construction of new bypass tunnels.

The prerequisite for the accident was the accelerated construction of the deep-level section for the 25th Party Congress. The tunnels between the "Lesnaya" and "Ploshchad Muzhestva" stations (the former is 14 meters below the latter) with a length of 450 meters were supposed to pass through a layer of Quaternary water-saturated deposits and water-bearing sands with water pressure of several atmospheres. At that time, it was considered impossible to bypass this aquifer, explaining that the sand layer here was thick and extensive. Deadlines were also pressing due to the need to open the country's first single-vault deep-level station — "Ploshchad Muzhestva." During the initial passage of the quicksand section (before the accident), standard cryogenic equipment was used — cooled brine was pumped ahead of the shield. The ground was frozen, and the shield passed through the section. After the accident, to quickly pass through the quicksand, a technology of freezing the ground with expensive cryogenic equipment was applied. To reduce the number of boreholes to be drilled, the number of pipes needed for freezing the ground, and the volume of freezing, engineers from "Lenmetrostroy" proposed an option of placing the tunnels one above the other. Although this significantly reduced the number of required boreholes and pipes, some experts believe it worsened the situation. During the elimination of the washout consequences, from 6,000 to 8,000 tons (according to various data) of liquid nitrogen were allocated. In the quicksand area, 15 freezing stations operated, 2,000 special boreholes were drilled, and the length of pipelines reached 350 kilometers.

On April 8, 1974, at about 16:30, during drilling of advanced exploratory boreholes in the lower tunnel, unfrozen soil was discovered, from which water was flowing. The quicksand at a depth of 90 meters had been detected much earlier, but freezing it was unsuccessful. The face began to fill with water through appearing cracks. Soon, the upper tunnel (which had no direct connection to the face) also began to fill. Emergency gates could not be fully closed due to the rapid inflow of quicksand, but all people were rescued. The tunnels were flooded for a kilometer, and a significant part of the frozen ground mass thawed.

Sinkholes appeared on Ploshchad Muzhestva and adjacent city highways, walls of houses and above-ground structures cracked. Traces of this incident remain in two production buildings of the NPO "Avrora," visible from Polytechnic Street: part of these buildings collapsed, and it was decided not to demolish them but simply to seal the floors from the street side. The penetration of quicksand into the metro tunnels was stopped by constructing a barrier near the "Lesnaya" metro station. To stop surface destruction, the workings were flooded — tap water was pumped into the emergency tunnels.

Repeated tunneling was carried out using ultra-low temperatures (liquid nitrogen with a boiling point of minus 196 degrees Celsius was used). This method was applied for the first time in world practice. To overcome the washout, nitrogen was supplied to Leningrad by all Soviet factories producing it. This allowed rapid work on creating a frozen soil plug and freezing the soil.

On November 30, 1975, the tunnel breakthrough was completed. The tunnel design was unusual, as was the washout situation: it had extraordinary strength. Journalist Stvolinsky wrote in the article "Road of Courage": "You walk along a hollow and smooth metal pipe stretched for hundreds of meters. Under your feet is the concrete track base laid on metal, behind the steel is concrete, behind the concrete are cast-iron segments. Only beyond them — the washout."

On December 2, a rally dedicated to the breakthrough was held at the "Ploshchad Muzhestva" station. On December 31, 1975, the entire section from "Ploshchad Lenina" to "Akademicheskaya" was commissioned with an "excellent" rating. At that time, the length of the entire Kirovsko-Vyborgskaya line from "Dachnoye" to "Akademicheskaya" was approximately equal to the length of the first Russian railway between Petersburg and Tsarskoye Selo.

The quicksand continued to wash out the tunnels throughout the section's operation, with a large amount of liquid entering the tunnels through drainage — about 60 cubic meters per day.

Since early February 1995, water inflow sharply increased. From February, the maintenance staff demanded a reduction in train speeds; from Friday evening until the start of service on Monday, the tunnels were completely closed for work.

Six months of efforts did not yield the required results, and on December 2, 1995, the newspaper "Saint Petersburg Vedomosti" published information:

"Due to urgent works on the metro section between 'Lesnaya' and 'Ploshchad Muzhestva' stations, from December 4, 1995, metro train traffic on the 'Ploshchad Lenina' — 'Akademicheskaya' section will be suspended every day of the week."

"Cracks appeared in the thick metal covering the tunnel lining rings inside the tunnels. Water with sand began to flow. This mixture eroded the metal like sandpaper. When trains were 'knee-deep' in water, and a 'shower' poured on the high-speed expresses from above, metro managers sounded the alarm... Installers screwed more than two thousand two-meter anchors into the upper tunnel's body, which became a kind of reinforcement. Then, behind the steel sheet stitched with anchors, a concrete mixture was pumped. By autumn, 60 meters of the most dangerous section in the upper tunnel, through which trains travel from 'Ploshchad Muzhestva' to 'Lesnaya,' were repaired. Feeling resistance, the element collapsed onto the lower tunnel. Repair workers clearly could not keep up with building protective reinforcements... On December 4, about 18 cubic meters of water-sand mixture burst into the section."

The tunnels could not be saved: on the night of December 5 to 6, the emergency headquarters decided to flood the two-kilometer section "Lesnaya" — "Ploshchad Muzhestva." The last use of the tunnel was the transfer of several trains from the "Severnoye" depot to "Avtovo." The trains were pulled by a diesel locomotive — the contact rail voltage was turned off for safety. Several train sets were sent to the "Nevskoye" depot, but by railway.

The newspaper "Saint Petersburg Vedomosti" reported: "On December 9 at 21:00, the gate at the lower end of the tunnel facing the 'Lesnaya' station was closed and welded. Immediately, its reinforcement with a concrete plug began."

Again, the tunnels were filled with tap water under pressure to prevent surface subsidence in the Ploshchad Muzhestva area and destruction of nearby buildings. During the suspension of traffic, city transport routes were changed: by Sobchak's order, a free bus route (No. 80) was organized; tram route No. 32 was significantly shortened and renumbered to No. 38. By February 14, 1996, a turnaround siding behind the "Lesnaya" station was restored, which had been used before 1975 when the station was a terminus. The "Ploshchad Muzhestva" station became a dead-end, using only one track; the connecting tunnel between the first and second tracks was located north of the station, i.e., toward "Polytechnicheskaya" station. It should be noted that until 1995, this turnaround siding never existed, but thanks to the station's design, its construction through the station complex's service rooms was completed relatively quickly. The first train arrived at the station on December 22.

Despite the introduction of the free bus route, it could not fully replace the flooded section, which greatly increased the load on some types of surface transport and on the metro stations of the Moskovsko-Petrogradskaya line — "Prospekt Prosveshcheniya," "Ozerki," and "Pionerskaya." The latter even operated in a special mode during morning and evening rush hours: in the morning — only entry, in the evening — only exit.

Only two train sets were used on the northern section of the Kirovsko-Vyborgskaya line; they traveled from "Devyatkino" station to "Ploshchad Muzhestva" and then departed from the same track they arrived on, returning back. Trains ran on schedule with an average interval of 10-15 minutes during the day and 15-20 minutes in the evening after rush hour; the schedule was posted at each metro station of the cut-off section.

Specialists from "Lenmetrogiprotrans" prepared several projects to restore the emergency section, mainly including the construction of bypass tunnels. Among the proposed options for eliminating the accident, the project for constructing new tunnels with the participation of the Italian company Impregilo NCC was chosen (a 20-year warranty was given, which is short since the first tunnel lasted almost as long).

The tunneling shield "Victoria" began constructing a new route about 200 meters away from the old alignment and 20 meters higher. There were funding difficulties during the elimination of the "washout." The washout became a tool of political struggle; promises to solve the problem were made by everyone — from deputies at all levels to the governor of Petersburg (Yakovlev). The new governor (Matviyenko) named the deadline: the end of June 2004, and the elimination of the washout consequences was completed.

The elimination of the "washout" consumed significant resources from the federal and city budgets and effectively slowed the development of the Saint Petersburg Metro for several years. (According to some data, the total cost of the work exceeded $145 million, half of which was contributed by the federal budget, the other half by the city.)

The new tunnel is called the "caterpillar": it has rubber joints and can oscillate together with the soil.

The "washout" section is under constant monitoring; according to metro employees, there are no grounds for concern that a situation similar to that on the Kirovsko-Vyborgskaya line in 1995 could occur elsewhere in the metro.

Construction chronology:

November 21, 2001 — the tunneling shield "Victoria" was lowered into the shaft.

February 2002 — tunneling began.

March 2002 — the "Victoria" shield settled half a meter in the tunnel, and the Italian-Swedish contractor — a consortium of Impregilo and NCC companies — faced huge penalties; the tunnel commissioning for the city's 300th anniversary was seriously in doubt.

April 11, 2002 — tunneling work was stopped.

June 2002 — visit of the government commission of Gosstroy.

June 26, 2002 — the Italian government discussed the unsatisfactory work of the "Impregilo" company in Saint Petersburg and appointed a government curator — the "Rocksoil" company (Italy).

July 2002 — the Russian Tunnel Association completed the examination of the modified part of the design documentation and issued a positive conclusion (changes were required after the April incident). The consortium made changes to the shield design and carried out its upgrade.

August 2002 — the tunneling complex passed test trials after the April stoppage and modernization.

September 4, 2002 — tests were stopped again.

September 20, 2002 — tests were finally completed.

December 6, 2002 — the tunneling complex, moving at high speed, hit "hard underground formations" (according to some data — a concrete collector, according to others — glacial boulders). As a result, many tunneling drills were broken. French divers had to be called, who worked under pressure of more than 5 atmospheres. Work had to be stopped for several months.

January 2003 — repair completed and tunneling resumed.

May 5, 2003 — tunnel passage in one direction completed. Repair of "Victoria" and preparation for digging the second tunnel.

August 27, 2003 — start of working tunneling of the return tunnel from "Ploshchad Muzhestva" to "Lesnaya."

November 27, 2003 — tunneling works completed.

May 26, 2004 — the first test train passed through the new section.

June 5 — "Vyborgskaya" and "Lesnaya" stations closed.

June 12 — stations north of the "washout" were closed.

To ensure passenger transportation, the free bus route No. 80 was extended to "Ploshchad Lenina" and the Finland Station. Also, bus line No. 100 to the Ruchyi railway station was activated. The construction was planned to be completed by the 300th anniversary of Saint Petersburg, but the restoration of through traffic on the 1st line took longer. On June 26, 2004, Russian President Putin solemnly opened the section, traveling through the former washout tunnel on a special train consisting of two cars. As metro builders promise, the washout problem is closed for at least 50 years. At 19:20, passenger traffic on the emergency section was fully restored, and the washout became history.

Metro builders working on eliminating the washout had to pass through the emergency section frozen to ultra-low temperatures. At the face, the temperature dropped to minus 50 degrees Celsius. Workers wore felt boots and several pairs of pants.

When a real threat of destruction hung over the houses on Ploshchad Muzhestva, residents' feelings were often overheated by the press. For example, all of Russia was alarmed due to flooding of Polytechnic Street with water caused by a pipeline rupture hit by a passing truck. When water from the pipe began flooding the surface part of the washout, people feared an underground catastrophe.

After part of the buildings collapsed following the washout, a man could be seen on the street offering a large sum of money to a brave person who would enter his destroyed office and carry out a certain briefcase.

The tunneling shield "Victoria" was specially created for this project: such tunnels will no longer be built. Therefore, it was planned to install it somewhere as a monument (a debatable claim; according to other data, "Victoria" was already used. It was simply modernized for this work). It was 0.5 m in diameter wider than standard tunneling shields, which caused specialists to worry about the reliability of the resulting tunnel.

The quicksand freezing project was developed by GIPKh (Leningrad, State Institute of Applied Chemistry). Following the successful passage of the emergency section, its employees were supposed to be awarded. However, GIPKh management rudely refused further cooperation with the metro builders. The prepared award sheets were canceled.

Remnants of pipes through which liquid nitrogen was pumped can still be seen in the Lesotechnical Academy park.

During the operation, due to nitrogen vapors being heavier than air, local residents were evacuated. Excess gas was discharged to a height of 100 meters using special installations.

In Saint Petersburg, in memory of the "Washout," bus routes No. 80 and No. 100 will never be used again. The free bus No. 80 ran between the "Ploshchad Muzhestva" and "Lesnaya" metro stations from December 1995 and made its last symbolic trip on June 29, 2004. Bus No. 100 (also free) operated from June 12 to 20, 2004, between the Ruchyi railway station and the "Ploshchad Lenina — 2" metro station.

Groundwater in the Saint Petersburg Metro

1950 — For the construction of the "Ploshchad Vosstaniya" station, to combat groundwater at the site of the former Ligovsky Canal bed, a caisson was used for the first time in the Leningrad metro.

1954 — washout during the construction of the first phase of the "Avtovo" metro. Waters of the Krasnenkaya River seeped into the pit. Elimination by brine freezing. The station stood until 2005; repairs began in 2006 and were expected to finish in 2009.

1955 — soil collapse during the construction of the inclined passage of "Pushkinskaya." Due to the elimination of consequences, the station was commissioned later than other stations of the launch section.

During the construction of the "Ploshchad Vosstaniya" — "Ploshchad Lenina" section (commissioned in 1958) — the Koven washout, an ancient branch of the Neva, was located at the section between "Ploshchad Vosstaniya" and "Chernyshevskaya."

During the design of the Moskovsko-Petrogradskaya line, a station was planned near Mars Field, but reconnaissance revealed not only an underground river flowing there, which caused the Koven washout, but also that the Neva's bottom had a depression at this point. It was decided to bypass the underground river from below. This decision resulted in the famous slopes with a steepness of 60 thousandths (the so-called "roller coaster") and the absence of a metro station near Mars Field.

1975 — washout during construction.

1993 — penetration of groundwater into tunnels on the "Chyornaya Rechka" — "Pionerskaya" section exceeded allowable daily norms. Repairs began, lasting exactly ten years. They were carried out exclusively during night windows, so only the earliest passengers noticed the traces.

1995 — breakthrough of the operating "Lesnaya" — "Ploshchad Muzhestva" section.

During the operation of the "Prospekt Prosveshcheniya" — "Vyborgskoye" electric depot tunnel, there were large leaks. There are no underground rivers in this area, but tunnels intersect water-saturated horizons; an extensive system of lakes formed on the site of flooded peat workings is located close to the depot and tunnels. According to the official version of city authorities, this problem influenced the decision on the opening dates of the "Parnas" station.

During the construction of the transfer tunnel from "Dostoevskaya" to "Vladimirskaya," an incident occurred related to water penetration into the workings. The situation was corrected in less than a week. During the incident, train traffic was not stopped; trains passed the station in transit with speed restrictions.

2008 — increased penetration of groundwater into tunnels on the "Staraya Derevnya" — "Komendantsky Prospekt" section, built in the late 1980s but commissioned only in April 2005. Repairs began, carried out during night windows.

Sources:

https://ru.wikipedia.org/wiki/Размыв_в_Петербургском_метрополитене

https://www.spb.kp.ru/daily/26402.5/3278346/

https://subterramuseum.ru/library/lectures/razmyvy-v-metro-prichiny-i-likvidatsiya-posledstviy/

https://dic.academic.ru/dic.nsf/ruwiki/1115189