The Severomuiski tunnel is located in one of the most isolated and hostile areas of the globe. A place where links with the rest of the world are few, regional development is limited, and the climate conditions range from -40°C for weekly averages in the long, dark winters to highs of +40°C in summer.
Severomuiski is the longest of 11 tunnels totalling 33km on the 3,300km long Baikal-Amur Magistral (Railway), or BAM, to link (from the west) the existing Ust-Kut railway station on the River Lena in central Siberia to Komsomolsk on the River Amur in the far east (Fig 1). Passing to the north of magical Lake Baikal - the largest and deepest body of fresh water on the planet - the line was approved in the early 1950s during Stalin’s rule of the former Soviet Union to provide a second Siberian rail route to Vladivostock. The first TransSiberian line, running 1,000km to the south and along the Chinese boarder, was considered vulnerable to potential military action by Russia’s powerful Asian neighbour. The new line was also intended to open up central and eastern Siberia to mining and other primary industries including logging.
At 15.3km long the tunnel passes through the 20-30km-wide Severomuiski mountain range which forms the watershed between Lake Baikal and the River Vitim and has peaks that rise to 2,500m high. In addition to wide zones of permafrost and many thermal hot springs of up to 60-70°C, the mountainous region is highly seismic with up to 360 earthquakes of between 1-4 on the Richter scale shaking the region per year.
Work on the politically high-profile railway started in the early 1970s with excavation of the Severomuiski Tunnel starting in the mid-1970s. Since then tunnelling crews and engineers have persisted doggedly to complete this often-cursed tunnel. A last blast finally achieved hole through on March 30, 2001, some 27 years after starting, to reward all who had dedicated much of their lives to the project.
The tunnel passes through a most complex series of weathered, faulted, and tectonically disturbed granite. Along with hundreds of smaller faults of between 10-50m wide (as many as 300 encountered during excavation) four major fault zones of up to 800m wide were identified and expected to present serious difficulties (Fig 2). Nothing however could prepare tunnellers for the reality.
During early planning, a twin tube, double track facility was advocated to match the rest of the line, but the alternative smaller 18m2 pilot tunnel, parallel and about 15m from the axis of a 60m2 single-track main tunnel, prevailed. The pilot was proposed as a high-speed TBM drive, using, for the first time in Russia, imported hard rock TBMs. As well as providing advanced notice of geological conditions along the main tunnel alignment, the pilot would provide drainage, improve ventilation and present an opportunity for additional points of attack.
Five divisions of the former Soviet Union Ministry of Transportation Construction were assigned to excavate the tunnel (Table 1). After gaining access to the remote locations, work started with the sinking of an original three planned intermediate access shafts and procurement of two TBMs for the pilot tunnel.
The plan was to have pilot excavation progressing from both portals and up to 300-400m ahead of the main tunnel portal headings. Main tunnel excavation would also progress in both directions from the intermediate access shafts once excavated, to have the tunnel completed by 1987, ready for inauguration with the rest of the railway.
For the pilot a 4.5m diameter Robbins machine was launched in January 1978 at the east portal, and was followed in May 1979 be a 4.56m diameter Wirth TBM to progress from the west portal. True to their primary purposes, the pilot tunnel drives warned early of the incredible difficulties to be encountered. From the start, the pilot TBMs were plagued by huge and sudden flush flows of water mixed with sand and rubble that clogged and jammed the cutterheads.
|Table 1: Six construction divisions worked on the tunnel|
|TO-21**||920.4m||4,318m||1978 to final completion|
|TO-27||Built the housing camps and surface installations|
TO = Tunnelling Division of the USSR Ministry of Transportation Construction
**TO-21 is now restructured as the BAM Tunnelstroy Construction Management division of the part privatised BAM Tunnelstroy joint stock company headquartered in Yekaterinburg in central Siberia
Although fault zones were anticipated, their full extent was only defined by aerial and satellite geological surveys undertaken once construction had started. Earlier investigations were only possible at the portal zones. The first of the four major regional faults, called pass, was identified as running parallel with and along the tunnel alignment axis from the eastern portal. The second, called the Angarakan Depression, located near the western portal, was defined as a 65km long feature that would create a fracture zone of some 400m wide at tunnel alignment. The third zone, located near Shaft 3, predicted mainly seismic and tectonic discontinuities and faulting and fractured rock in bands of up to 10-15m wide and 5-6m deep. The fourth major fault zone, by far the most powerful and extensive, and anticipated to harbour vast volumes of ground water and highly weathered and fractured rock, lies just east of Shaft 1 and would extend for about 800m at tunnel elevation.
In each of these fault zones, major changes to original design parameters and alternative excavation methods would be required. At an early stage, cored probe holes ahead of the tunnel faces became mandatory both to investigate conditions and provide information on which redesign specifications and excavation methods could be based.
The first major inrush came early, on the Wirth TBM pilot drive as it was working through the Angarakan Depression from the west portal. The situation was retrieved by installing comprehensive dewatering systems both from the surface and from within the tunnel headings. A fourth access shaft was also sunk to attack the fault zone from the opposite side and uncover the buried pilot TBM. In this particular zone and for the first time in the industry, drill rigs were used to drill horizontal and inclined drainage holes of up to 500m long. Millions of cubic meters of water were extracted and eventually the pilot drive restarted.
From the east portal, also under the influence of extensive surface dewatering systems, the Robbins TBM made reasonable progress through similarly disturbed geology. At every turn tunnellers were met with setbacks. Even crossing minor faults of 10m wide resulted in major flush flows of sand, water, mud, and rubble. Eventually, the Robbins TBM came to a final stop at Shaft 2 after completing 6.7km of the pilot tunnel, setting a monthly advance best of 308m.
To make up for time lost at the west portal, a second Wirth TBM, was procured and launched from the bottom of Shaft 2 to advance westward toward the ominous fourth fault zone. This open gripper machine completed a further 4km of the pilot before being stopped. Meanwhile the first Wirth TBM was eventually completely defeated by the strata approaching the fourth fault zone. Conditions beneath an overburden of some 320-360m were described as "extremely nonhomogenious" and "appearing as if rock debris were swimming in the running clay-sand substance. The permeability coefficient was so low that the ground would not give off the water."
To tackle this material a third Wirth TBM was procured to start a new pilot heading eastward from Shaft 1 toward the fourth fault zone. This time, the machine was shielded and had a larger 5.76m diameter to install a heavy cast iron segmental lining. It was also launched on a new alignment to avoid adverse stress-redistribution affects on each tunnel. After only a few hundred meters however, it was evident that this TBM was also being defeated by the geology and it was withdrawn. It was said that the machine went on to work successfully excavating metro running tunnels for the city of Yekaterinburg in north-eastern Siberia. Excavation of the pilot from Shaft 1 continued using hand mining and hand-held drill+blast methods.
Work on the main tunnel headings encountered the same difficulties only magnified by the larger 8.5m and 9.5m diameter profiles. Like the modern TBM technology imported for the pilot, the main tunnel drives were also geared with state-of-the-art imported tunnelling equipment. This included Atlas Copco drill rigs, 3- boom gantry-type drilling jumbos from Tamrock of Finland and Furukawa of Japan, powerful loaders, heavy load haulage vehicles and muck cars, modern shotcrete units with imported additives, 12m long travelling concrete lining shutters, and high capacity concrete pumps. Where ground conditions permitted, monthly progress was as much as 200m/heading on the main tunnel drive and more than 300m/heading in the pilot tunnel. But all efforts were humbled by inrush volumes up to 4-5,000m3/h under hydrostatic pressures of up to 30 bar!
At Shaft 2, the deepest of the four shafts at 335m, water inflows were so great as to flood the shaft. To control this ingress three sumps fitted with 10 x 300m3/hr capacity pumps were installed.
In addition to dewatering and drainage systems, other techniques were employed to control water ingress and consolidate fractured rock. Ground freezing using liquid nitrogen was used at Shaft 2 and, although successful, was too expensive to apply on the scale needed. Grout injections, using various grout compositions from cement-silica to claycement and chemical polymer, were introduced and applied under subcontracts by Soletanche of France and Kokinboring of Japan.
Chemical grouting proved most successful. It was used to treat more than 180 faults, each 10-80m wide and for a total of more than 1.5km, and was perhaps the single most influential technique contributing to the survival and ultimate success of the whole tunnel project. Another technique used effectively and often in conjunction with chemical grouting was forepoling using 32mm diameter x 25-30m long rebar in various configurations to create protective umbrellas over unstable faces in fault zones.
Several immediate and permanent lining systems were used. These included permanent cast iron segments erected in the shield driven sections as well as reinforced insitu concrete linings with various drainage and waterproofing systems. Through the 550m long Angarakan Depression, the final lining of the main tunnel comprises 1m thick x 4-5m wide compartments of concrete filled steel cased panels with pre-installed rebar. The surface dewatering system in the zone, comprising 240m deep wells on 20m centres, was maintained until after this permanent lining was installed however once discontinued, about a year after excavation and over the following 20 years, high deformation of the robust permanent lining was recorded. Special expansion/deformation joints between the steel panels were installed every 36m to compensate as the full hydrostatic load of the restored ground water table came to bear. In 2002, during the TunnelTalk visit, the lining was said to be performing well under stabilised conditions.
It was clear from an early stage that the tunnel would not be completed in 1987 as planned. It was decided a detour should be built to allow for the line’s inauguration. The bypass, comprising 25km of track, opened in 1984 but, with gradients of up to 40‰, three heavy-duty electric locos were required to pull each train over the pass. As tunnel delays lengthened and costs increased, a second bypass with two hairpin tunnels of 1.7km and 800m long to reduce gradients to 18‰ maximum, was built and opened in 1989. During the dark days of the mid-1980s it was said that a special BAM committee, established to assess the situation, seriously considered complete abandonment of the tunnel and use of the second detour as the permanent mountain pass. However, at 56km long, trains on the second detour take 1.5 hours to complete a journey that will take 12-15 minutes through the 15.3km long tunnel, on maximum 7‰ gradients and at train speeds of 60-80km/hr. It was this fact and the determination of the tunnellers that saved the project.
In 1990, with the headings separated only by the dreaded fourth fault zone, the project was faced with a different crisis - the political collapse of the USSR. In the general economic decline during the first years of the ‘new Russia’, the project suffered serious funding problems. As well as severe shortages of materials and supplies, wages were often up to eight months in arrears. By working on, under extreme living and working conditions, the tunnellers ensured that the project once again survived. The crisis was eventually overcome when the new Russian Railway Ministry secured a stable source of project funding.
Following this, the project had to survive the upheaval of the country’s on-going so-called ‘democratic revolution’. The impact on the project was the restructuring of the tunnelling divisions of the former USSR Ministry of Transportation Construction (TOs) into ‘open-ended joint stock companies’ or OAOs with private enterprise shareholders and a majority holding retained by central government. At Severomuiski, TO-21 was restructured into the BAM Tunnelstroy OAO and, together with the Construction Management Division of the company, was charged with completing the tunnel project.
In 1997, with stable funding in place, a final push was initiated to complete Severomuiski through the last, fourth fault zone in the shortest possible time. This effort was rewarded at the end of 1997, on December 5, with final hole through of the pilot tunnel. But over the final meters of the main tunnel drive, an enormous collapse of material and inrush of water occurred. Once again a new plan was needed to recover. This took the form of a 1 km long drainage tunnel excavated parallel to and off the main tunnel.
Again highly successful chemical grouting was undertaken to stabilise the situation and allow main tunnel excavation to restart.
In the most difficult conditions excavation started with small side wall adits at the main tunnel invert that were backfilled with concrete before excavating the full cross section in multiple phases on a top heading and sequence of three benches (Fig 4). The composite lining of steel arches and reinforced concrete cast behind steel formwork panels was built as an integral part of the phased excavation cycle. For the final 400m through the heavily chemically grouted zone, cast iron segments were erected within an open-face shield, followed by a permanent reinforced in-situ concrete lining.
Main tunnel breakthrough finally occurred on 30 March 2001 and the two headings of the drainage tunnel were then also holed-through in September 2001 to provide for continued drainage of still high volumes of ground water ingress. Even today, with the tunnel lined and treated to control water ingress, ground water flows at the portals measure regular volumes of 800-1,000m3/hr/tunnel kilometer. Some 3,500m3/hr flows from the 7km of uphill tunnel from the west portal and another 6,000m3/hr over the 8km of uphill tunnel from the east portal.
The triumphs of these breakthroughs however were overshadowed by a final irony. In 1998 Russia’s economic and financial meltdown completely wiped out any savings or pension funds that workers and engineers might have accrued over their years of employment in Siberia. It also threw the project once more into financial crisis. With previously secured funding, the project avoided having to borrow further funds, but the crisis did impact those owning money to BAM Tunnelstroy. These included government client organisations. In an ever tightening and vicious circle, TunnelTalk was told that OAO part-privatised joint stock companies like BAM Tunnelstroy must pay corporation tax, but that delayed payments from clients resulted in interest owed on late payment of taxes. The government owes some US$143.3 billion in foreign debt as a result of the former Soviet collapse and the 1998 economic crisis. Paying this debt is a heavy burden on the country’s fledgling capital-market based economy.
Fortunately for BAM and the Severomuiski Tunnel, future financial uncertainties will have no effect. After completing the finishing works the first train passed through the tunnel in December 2001 and official inauguration is planned for December 2002.
In addition, through years of struggle and setback, Severomuiski escapes the label of a tunnel defeated by political, financial or geological difficulties. Where other projects such as the Supercollider project in the United States were stopped due to withdrawal of government administration support, Severomuiski was not. As a tribute to tenacity and inventiveness, the first tunnel to be defeated by geological conditions alone is yet to materialise.
At the regional head office at Nizhneangarsk on the north side of Lake Baikal, Technical Department Manager, Valerian Kutylovsky and Leonty Tikhonov Deputy General Direct (Economics), presented an informative introduction to Severomuiski, but it was after a 300km, 10 hour drive to the project site, that Kutylavsky with Vladimir Fediukin, General Director of BAM Tunnelstroy’s Construction Management division, and Victor Voloshko and Gennady Terzimanov, Deputy Chief Engineers, related the full story.
As TunnelTalk continued its tour of Russian tunnelling projects in September/October 2001, it met with several senior management engineers who had worked at Severomuiski - among them Vladimir Bessolov, formerly Chief Executive Officer of the Serevermuisk Tunnel from 1977 to 1991 and now Project Manager of the Lefortovo Highway Tunnel in Moscow, and Marat Rakhimov and Yuri Nosson Senior Engineers for KazMetroStroy on the Metro project in Kazan. With each meeting this epic project was discussed and it soon became obvious just how extreme conditions were. Severomuiski certainly deserves its place in the international tunnelling hall of fame.