Among the many projects underway in China and being bored by shields from NFM Technologies/NHI, the tubes being excavated for the Yintao water tunnel, in Gansu province, and the rail tunnels near Tianjin, south east of Beijing, face contrasting geological challenges with their quite different lengths and environments.

NFM/NHI has supplied two hard rock shields to Yantao for two consecutive long drives that form only part of the colossal water conveyance scheme, and two slurry machines for separate tunnel works to create an urban link tunnel in Tianjin, and at the east end of the high-speed extension from Tianjin to the district of Tanggu, to the south east and next to the coast.

Geology on the Yantao drives comprises extensive single tube bores through granites and schists and other rocks of varying intact structure and stability, ranging from good to weak, across the rural landscape. The much wider but shorter urban bores at central Tianjin and Tanggu district have to contend with classic alluvial conditions of soft ground and high water tables.

The tunnelling works at the Yantao drives have been underway for much longer than on the city centre rail bores where the Tanggu shield has yet to commence excavation, and will do so as the Tianjin TBM nears completion of its run.

Taken together, the projects help show some of the range, scale and nature of many of the tunnelling schemes underway across the country.

Yintao water tunnel
The Yintao project is a major water transfer scheme under construction in north west China to improve industrial, urban and agricultural development, especially for growing maize and cotton on irrigated land. It is one of a number of large, statesponsored projects to strategically share and redeploy water resources from the south to northern areas.

Yintao has two parts to the overall scheme – the Jiudian Gorge Water Control Project and the Water Supply Project, respectively. The latter is being constructed in two phases and will divert water from the Tao River, a tributary of the Yellow River. Tunnelling for the first phase is underway, and includes 18 tunnels with a total length of almost 97km.

Excavation of the sections of the water transfer tunnel will be mostly by TBM with only a minority by drill and blast. Other major civil engineering structures and works on the scheme include three main canals with combined length of 150km and 12 pipelines totalling more than 113km.

Construction work on the overall Yintao scheme began in 2006 but, for the first phase, excavation of the two drives (T7, T9) at the northern end of the main tunnel alignment commenced in 2009. For the tunnelling works two NFM/NHI hard rock TBMs are being employed, and the contractors are: China Railway Tunnel Group (CRTG), on T7; and, the Chinese- Italian JV contractor CMC Ravena with Sinohydro Engineering Bureau 4, on T9.

The TBMs are driving comparable lengths of approximately 17-18km and while they are both 5.75m diameter, and the standard internal diameter of the concrete lining is 4.96m, they are not a pair. One is a short single shield, the other a short double shield – the former arrangement having been elected to help counter potential difficulties with a stretch of squeezing ground along the alignment, which passes through clay and argillite.

Geology on the route of the double shield is mostly rock, comprising silty sandstone with granite, gneiss and marble inclusions, with no risk of squeezing conditions. Both TBMs are driving at altitudes of approximately 2200m a.s.l., and cover to the alignments is up to 350m.

Tunnelling – Yintao
The two hard rock TBMs were launched just over a year ago, both boring southwards. The machine on the T7 section set off in December 2009 and the double shield was launched on T9 in February 2010.

On the T9 drive, the double shield has a total thrust of 21,420kN and its nominal and breakout torques are 5,000kNm and 6,350kNm, respectively.

Like the single shield on T7, the rotation speed of the cutterhead is up to 7.9rpm with seven electric motors and the maximum speed of advance is 120mm/min. Their cutterheads are equipped with disc and reamer cutters, and have vertical offsetting of 50mm.

The backup train on T9 has 15 gantries whereas there are two more on T7.

By late April 2010 each machine had bored more than 2.5km, and their best weekly advances had then achieved 252m (T9) and 317m (T7), respectively.

The performance rates on the T9 machine have continues to improve and in September 2010 the best weekly advance reached 434.6m.

By then, the progress rates for the best day and month were 86.7m and 1463.7m, respectively, and achieved in conglomerate with boulders, gravel and sand and some mud content, more than 10km, or almost 60 per cent, into the 18.25km long drive. The double shield is erecting lining of 1.6m long rings of 280mm thick hexagonal segments, each weighing 5.2 tonne and four to a ring.

Utilisation rates saw 49 per cent of the time in excavation, 27.8 per cent in regripping and 18 per cent dealing with faults and corrective maintenance. Slightly more than 5 per cent of the time was taken by cutter changes and planned maintenance. The TBM is working with an electrode system to scan the ground up to 30m ahead of the face for problem areas as well as suitable sections to help plan maintenance works, says NFM/NHI.

Since then, those best day, week and monthly advance rates remain in place and the TBM had bored a total of 11,542m by mid-February 2011, a year into the drive.

However, the TBM on T7 – having bored 2633m by June last year – has been at a standstill for the last eight months. Details surrounding the stoppage, and plans for the remainder of the drive, were not immediately available.

To date, almost 14.2km of tunnel has been excavated on T7 and T9.

Tianjin rail link – tunnels
Global financial centres carry ever more weight today and the latest being developed, by China, is in Yujiapu in the Tanggu area of the key city of Tianjin. Naturally it is attracting significant investment in transport links, one of the key elements of which is extending the highspeed rail line out of Beijing to Tianjin through to the Tanggu and Yujiapu areas.

The main line is designed to have ‘Bullet Train’ services run faster than 300km/h and came into service two and a half years ago. Once completed, the extended line will allow journeys between the Beijing and Yujiapu in less than an hour. The current, 120km long journey from the capital to Tianjin takes half an hour, and the extension will add a further 60km link between Tianjin and Yujiapu where the trains would travel at more moderate speeds.

At the eastern end of the high-speed extension, in Tanggu, to take the link into Yujiapu financial district the line goes into a twin-track, single tube 10.6m i.d. tunnel that runs near the Haihe River.

Geology comprises sand, clay and silt, and the groundwater level is high in the river zone. The overburden along the tunnel alignments ranges from 7.5-15.6m. The 2.25km long tunnel is being built mostly by TBM with a relatively short section constructed by cut and cover methods.

The contractor is China Railway Construction Corp’s (CRCC) Bureau 16.

Separately, towards the western end of the new link, in Tianjin, a tunnel is to be constructed to connect two key stations in the city – Tianjin West and Tianjin. The interconnection tunnel – Dongguan – will help to make Tianjin West station one of the largest rail hubs in the country, connecting into the existing high-speed line to Beijing and a number of others.

The Dongguan tunnel is to be 5km long with about 42 per cent of the length bored by TBM. Early in the drive the shield is to pass below the Haihe River with only about 9m cover – less than the tunnel diameter.

TBMs
NFM/NHI have designed and delivered two Benton’ Air shields to bore the separate tunnels – the link into Yujiapu financial district and the interconnection between the stations in Tianjin, respectively. The company says that due to the soft ground, high head of water from the groundwater level and the large bore excavations needed in dense urban environments it was decided that slurry machines should be used.

The TBM on the Dongguan tunnel was launched in September 2010 and is due to complete its drive by August this year. NFM/NHI reports that good progress is being made with availability rates high – above 95 per cent since launch.

Excavation of the Tanggu/Yujiapu bore, at the end of the high-speed extension, is scheduled to start in June this year. The TBM will be launched by CRCC slightly west of Tianjin station, on the east bank of the Hiahe River, and then pass below to the west bank and run almost parallel to the channel before turning west and rising to finish the drive.

The TBM will have main thrust of 140,700kN, and cutterhead power and speed of 2030kW and up to 2.5rpm. The nominal torque from the cutterhead drive is 17,500kN.m

Concrete lining for the Tanggu/Yujiapu bore is to be formed of 1.5m long rings built from 500mm thick segments.

From the TBM bored section towards, but stopping short of, Tianjin West station the final section of the Dongguan tunnel will be built by cut and cover.


Location map of Yintao water tunnel showing T7 and T9 sections Geology along the T9 section on Yintao water tunnel, being bored by double shield NFM/NHI machine TBM utilisation on tunnel T9, Yintao project Hard rock TBM from NFM/NHI for T9 drive of Yintao water tunnel Longitudinal profile of TBM and backup train about to bore T9 section of Yintao Rail link tunnels in and near Tianjin NFM/NHI 11.97m diameter slurry TBM for Tianjin’s interconnection tunnel