A major rail tunnel project is under construction in west China, in Qinghai province on the line to Tibet. Bypassing the existing 4km long Guanjiao tunnel – a not insignificant structure itself in this remote region – the 32.6km long twin tubes are being slowly pushed through the base of the mountain barrier, helped by a rake of drill and blast adits.

The new rail tunnel will take on the name Guanjiao tunnel as it will replace the existing single tube, which sits high up the ridge. It is approached and departed from with difficulty by trains requiring extra engines to pull and brake along the exposed, looping tracks through the steep terrain.

The project site is on the Qinghai-Tibet (‘Qingzang’, ‘Qinghai-Xizang’) railway and lies to the west of Qinghai Lake and Xining, the capital of the province. At present, trains need to negotiate the rise of the tracks to the existing tunnel before easing down the far side of the ridge to then proceed further west to small settlements, like Ulan and Haixi and the next major stop at Golmud.

Then, turning southwest, the trains proceed onward through dozens more stations across the Qinghai-Tibet plateau and then into the Tibet Autonomous Region, to terminate after 1142km in the capital, Lhasa.

With recent investment and work that constructed that link to Lhasa by 2005, at altitudes of mostly more than 4000m, there is greater need, as expected, for bottlenecks along the previously established line to be removed. Bottlenecks such as the exiting Guanjiao tunnel, built a quarter of a century ago as part of the 815km long Xining-Golmud section. Xining itself was reached by rail in 1959.

When the new tunnel is completed, as part of the wider scheme to add a second line to Xining-Golmud section, the capacity of the entire railway will increase by half to 6 million tonnes annually.

Other key tunnels along the Xining-Lhasa route are the 1338m long Fenghuoshan tunnel, at an altitude of 4,905m, and the 1686m Kunlunshan which was driven through permafrost with complex geology and fracture zones. Aside from the existing Guanjiao tunnel, the longest tube on the route is Yangbajing, at 3345m.

Guanjiao Tunnel – Brief Overview
To bypass the existing Guanjiao tunnel there were three alternative alignments considered to cut through lower corridors in the mountain ridge, which had approximate lengths of 13km, 21km and 32km, respectively. The latter was selected and, while the longest, was also straightest and would give the highest transit speeds for trains – up to 160km/h.

The studies for the scheme also examined alternative excavation methods, using TBMs or drill and blast – each with different requirements for a series of long adits to provide both intermediate access and ventilation support.

Geology along the alignment corridor is extremely complex, both in the main bores and for the adits, and includes igneous, metamorphic and sedimentary rocks. There are a wide range of adverse ground conditions in different pockets of the project from high rock stress, karstic limestone areas and many fault zones to mud inflows and stretches of especially difficult groundwater ingress.

Construction work on the new Guanjiao tunnel began in late 2007. The parallel, single-track main bores are being constructed to run 40m apart and together call for excavated cross sections of approximately 90m2. The project is due to be completed by 2011-12.

To be built approximately 300m lower on the mountain than the existing tunnel, the portals of the new tunnel are at elevations of 3381m and 3324m above sea level respectively. The new Guanjiao tunnel slopes upwards from the portal at approximately 10 per cent on the eastern side and from about the middle region runs back down at 11 per cent to the west exit. Overall, the new route will cut about 4km from the present, prolonged train transit of the mountain.

Work on the project is split into two sections: west and east, with lengths of 15.25km (total tunnelling 30.5km) and 17.35km (total 34.7km), respectively. The west portion is being undertaken by China Railway Tunnel Group, part of China Railway Engineering Corp (CREC), and the slightly longer package in the east by China Railway 16th Bureau Group, which is a subsidiary of China Railway Construction Corp (CRCC).

While the total distance to be excavated for the main bores is approximately 65km, cumulatively, at more than 15km in combined length, the adits constitute a major drill and blast series of operations in their own right and have been much of the focus of the construction so far. Chinese tunnelling sources say that following the drill and blast preparations there will be TBM-driven excavations on the main tubes.

There are 10 main adits (plus an additional short tube) that are constructed as long, inclined bores that reach down into the mountain to open up the main bores and provide sufficient access and egress for workers and plant as well as providing support for ventilation and spoil removal. Four of the adits (numbers seven-10) are in the west package and the other six in the east, along with the additional bore (Z1).

In the west the total length of the 7m wide adits is 5.5km. The bores range in length from the longest, at 2333m (No7), down to 1619m, 1126m and 443m (No10) respectively.

In the east, most of the adits are more than 1km long, ranging from 637m to approximately 2800m. The Z1 bore is 205m long.

Developments as the construction has advanced have seen adits split in two to provide two points of access to the main bore construction zones, to improve construction logistics and programme flexibility and speed.

Spoil removal is employing conveyor belts with rock transported by truck for processing by crushers underground before being transported to the surface.

Wet-shotcreting systems have been provided by Putzmeister for the east package.

Part of the challenge for tunnellers and plant workers in adits and main bores has been working in cold temperatures and thinner air at high altitude, which makes activity tiring and more of a strain.

Further railway extensions
An additional reason for the need to debottleneck the Qinghai-Tibet route and increase rail capacity is yet further expansion of the line – onwards from Lhasa to Zhanmu via Shigatse and to Dali via Nyingchi.

Last month construction of the 253km long, single-track extension west to Shigatse was formerly launched. It is to include 29 tunnels with the longest to be approximately 10.4km. Beyond high altitude construction and generally complex geology that is anticipated, as ever, the tunnelling and bridge foundation challenges along the route also include geothermal ground conditions. A number of research projects have been established under a task force to address the problems.

Another extension of the line is also being considered from Shigatse south to Yadong, near where Tibet borders with India, between Nepal and Bhutan.

China is also in talks for links to Nepal.

Farther back along the line, at both Golmud and Xining, there are also plans for yet more new branches, further increasing the importance of these regional towns.

The recent construction and ongoing plans are part of the China Western Development strategy.


Location of the new Guanjiao rail tunnel in the Qinghai region of Western China with comparison of old and new tunnel routes Preparations at Guanjiao rail tunnel with the Putzmeister wet-shotcrete equipment Major tunnelling works and adits support the main twin bores