In the past 50 years, mainland China has made great strides in the construction of railway, highway, metro and hydraulic tunnels, and in underground powerhouses. More than 20 railway tunnels over 5km long and three over l0km have been built or are under construction. The three longest railway tunnels on the mainland are the 14.2km Dayaoshan Tunnel on the secondary line of the Hengyang-Guangzhou railway (already built); the 18.4km long Qinling Tunnel on the Xi’an-Ankang Railway (under construction); and the 12.7km long Changliangshan Tunnel on Shuozhou Huanghuagang Railway (under construction). There are also a large number of railway tunnels in difficulty geology. A total of 5300 railway tunnels with a total length of 2500km have been built.
Although extensive construction of highway tunnels started rather late compared with railway tunnels, the number of highway tunnels has increased rapidly in recent years due to the construction of high-class highways or expressways. At present, there are more than 450 highway tunnels with a total length of over 120km, of which about 80 tunnels are over 1km each and four are over 4km each. The longest highway tunnel on the mainland is the 4.7km Huayinshan Tunnel in Sichuan Province.
Besides the highway tunnels already built or under construction, several longer highway tunnels are under design or in the planning stage. They are the 8.6km long Xingui Tunnel in Fujian Province, the 6.3km long Wuzhishan Tunnel in Hainan Province and the 6.1km long Zhegushan Tunnel and the 8km long Nibashan Tunnel in Sichuan Province. It is worth mentioning that two immersed highway tunnels, one in Guangzhou and the other in Yongjiang,have been designed and built by Chinese companies.
A total of 88.5km of metros in four cities – Beijing (41.6km), Tianjin (7.4km), Shanghai (21km) and Guangzhou (18.5km) – have been built. Construction techniques for running tunnels and stations have been greatly improved, especially the running tunnels of the Shanghai and Guangzhou metros, where shield tunnelling has been successfully used besides the ordinary mining method.
There are more than 400 hydraulic tunnels over 400km long, and more than 40 underground powerhouses. The diversion tunnel for the Ertan hydropower station is ll00m long, 23m wide and 17.5m high and is the largest tunnel on the mainland. International competitive bidding is usually adopted for the construction of hydraulic tunnels, which promotes the importation and application of advanced technology and equipment; wet shotcrete and TBMs have been wldely used.
Railway tunnels
Application of NATM: this method was first adopted in the Xiaken Railway Tunnel on the Wanggang Railway. The 65m long, 20m deep tunnel was constructed in heavily weathered strata, where rock is weak and fractured with a high groundwater content. In accord with NATM principles, the tunnel was excavated in large cross section by presplit blasting or smooth blasting. Rockbolts and shotcrete were immediately installed to control deformation and a secondary concrete lining was applied when this rock was stable.
Because of the success of NATM in the Xiakeng Tunnel, the method was rapidly introduced to other railway tunnels, and Chinese engineers have built many tunnels in difficult ground using NATM.
Construction of long tunnels: among a number of long railway tunnels is the longest double-track rail tunnel – the Dayaoshan Tunnel (14.2km); the longest single-track tunnel -the Mihualing Tunnel (9.3km); and the longest twin single-track tunnel – the Qinling Tunnel (18.4km). During construction of these long tunnels, different methods and equipment have been adopted:
(1) Construction of a double-track railway tunnel
The Dayaoshan Tunnel is on the secondary line of the Hengyang-Guangzhou Railway. The main strata through which it passes are: Devonian dolomitic limestone and marl; Sinian or Cambrian sandstone; and slate and plate shale, in which more than ten faults have been found. The tunnel was designed and constructed using NATM. Swedish TH 286 hydraulic drilling jumbos with four booms were used. The tunnel was excavated in full face and blasted using smooth and presplit blasting in the hard rock sections and by presplit and controlled blasting methods in the soft rock sections. Shotcrete and rockbolts were used for temporary support and cast-in-place concrete for the secondary lining.
The 465m wide No. 9 fault is a large local fault with plenty of groundwater, which made construction difficult. In order to pass through it successfully, grouting was performed from the excavation face to consolidate the surrounding rock and stop water inflow.
Much advanced equipment was imported from abroad for construction of the Dayaoshan Tunnel, the first time in mainland China, and three lines of mechanisation were formed on the basis of this equipment: the drilling, mucking and wheel-less transportation line; the rockbolt and shotcrete line; and the secondary lining line. Since then, traditional partial excavation has been replaced by mechanised full face excavation in favourable geology and has provided unique experience for building double-track railway tunnels on the mainland.
(2) Construction of a single-track tunnel
The Mihualing Tunnel is located between Bangtao Station and Genglong Station on the Nanling-Kunming Railway. The strata along the tunnel comprise Middle Triassic sandstone intercalated with mudstone; and siltstone with less groundwater. The tunnel was also designed and constructed using the NATM. However, as it is a single- track tunnel, the pattern of construction used on the Dayaoshan Tunnel could not be adopted here.
After several studies, it was decided that gantry drilling jumbos should be used. They were LZ- 120D gathering-arm loaders made in China for loading and shuttle cars used for mucking. In December 1994, the monthly rate of advance was 502.2m in the exit section and 266.8m in the entrance section and 769m for the whole tunnel. All the equipment was made in China, except for the gantry drilling jumbos. Construction of the Mihualing Tunnel is a benchmark for the other single-track tunnels on the mainland.
(3) Construction of a twin single-track tunnel
The 18.5km long Qinling Tunnel, located between Qingcha Station and Yingpang Station on the Xi’an-Ankang Railway, consists of two single-track tubes 30m apart. The tunnel, with a maximum depth of 1600m, passes through mainly composite granite and gneiss. A pilot tunnel for the second tube was driven by drill+blast and will be enlarged after the first tube is put into operation. In January 8 1995, the No.1 Engineering Bureau and the No.18 Engineering Bureau of the Ministry of Railways started construction of the pilot tunnel heading from both the entrance and exit portals.Equipment used included gantry drilling jumbos; 4-boom hydraulic drilling jumbos; ITC 312 loaders, etc., greatly improving construction effectiveness. In the very hard rock, maximum monthly advance was up to 456m and the average was more than 200m, the best advance rates for railway tunnels on the mainland.
For the construction of the first tube, two 8.8m diameter TBMs manufactured by Wirth were employed. The Tunnel Engineering Bureau and the No.18 Engineering Bureau of the Ministry of Railways began construction at both the entrance and the exit portals in December 1997 and February 1998 respectively. The best advance rate is up to 528.1m/month and 40.5m/day; average monthly advance rate is 312m. The central section of the first tube was excavated by drill+blast to fit construction programme requirements. The first tube broke through in August 1999.
Construction of tunnels in difficult geology: among the 5300 railway tunnels on the mainland, many were constructed in difficult geology. The construction of the tunnels on the Nanling-Kunming railway, which was opened in 1997, is a typical example of working in unfavourable ground. There are 258 tunnels with a total length of 194.6km on this railway. During construction, difficulties such as weak surrounding rock; high stress; shallow depth; uneven pressure; karst; water inflow; faults; gas; and high seismic intensity have been overcome one after another. Completion of the Nanling-Kunming Railway demonstrates that tunnels can be built in mainland China in almost all unfavourable ground conditions.
All the tunnels constructed in mainland China have been built by drill+blast except the Qinling Tunnel. Other construction methods such as the shield and immersed tube methods will be employed for building some railway tunnels in special geology. The Ministry of Railways is considering the Beijing- Shanghai high-speed railway crossing the Yangtze River in Nanjing by means of an immersed railway tunnel. The feasibility study is now under way.
Highway tunnels
Highway tunnels with large cross sections: building 3-lane highway tunnels is a pre-requisite when 6-lane expressways are being constructed. On the mainland, several tunnels with three lanes are under construction: the Shanxinpo Tunnel in Yunnan; the Kaoyishan Tunnel in Guangdong; the Tieshanping, Yixuedashan and Zhenwushan tunnels in Sichuan; and the Tanyugou Tunnel in Beijing, etc. The highway department has carried out research into the type of structure and the excavation method and support measures to be used in 3-lane highway tunnels, resulting in a number of useful findings, which have been used in the construction of the tunnels mentioned.
Highway tunnels under water: the 2761m Dapulu Tunnel, passing under the Huangpujiang River in south west Shanghai, was opened to traffic in 1970. This tunnel is the first highway tunnel under a river to be constructed by a shield on the mainland. The shield was a 11.3m diameter mesh type mechanised shield machine with a hydraulic mucking system.
On May 1 1989, another tunnel, the 2261m long Yan’an Donglu Tunnel, which passes under the Huangpujiang River, was driven by the same kind of shield. Because of economic development and increased traffic in the Pudong area, the third tunnel under the Huangpujiang, which is 2193m in length and is called the secondary Yan’an Donglu Tunnel, was constructed by shield and opened to traffic in 1996. Experience gained from construction of the three tunnels will be useful for future construction of large diameter highway tunnels under river by shield.
On January 8 1994, the first immersed tunnel in the mainland to be designed and built by Chinese companies – the Zhujiang Immersed Tunnel in Guangzhou – was commissioned. The 33m wide, 8m high tunnel, is 1239m long overall, includes 517.5m in approaches on both banks, 264m in the mined sections and 457m in the immersed tube section. It consists of two tubes for a highway (each tube containing two lanes), one tube for the metro and one small tube for cables.
On August 8 1995, the second immersed tube on the mainland, the Yongjiang Immersed Highway Tunnel in Zhejiang Province, was commissioned, which, with a width of l l.9m and a height of 7.5m, has a total length of 1019.5m and a length of 420m in the immersed section. Construction of the two immersed highway tunnels demonstrates that immersed tube techniques have been accepted on the mainland. At present, two new immersed highway tunnels, one in Shanghai and another in Yongjiang, are in design and will be constructed in the near future.
Metro construction
The first section of metro on the mainland was built in Beijing and was opened in the late 1960s. After that, the first section of the metros in Tianjin, Shanghai and Guangzhou were put into use in 1980, 1994 and 1998 respectively. There are in total 88.5km of metro lines in service in these four cities. During construction of the Beijing and Tianjin metros in the 1960s and 1970s, cut+cover was widely adopted because the buildings were widely spaced in these cities at that time. Between the 1980s and 1990s, shield and mining methods were adopted for the construction of metros to reduce disturbance on the surface and to avoid the relocation of surface buildings, underground cables and pipes.
During construction of the first line of the Shanghai Metro, seven shields were imported for driving running tunnels under busy streets. Advance rates were 4-6m/day on average, l 8m maximum; and 150m/month on average, 320m maximum. In the early 1990s, the shield method was also used for construction of the running tunnels on Line 1 of the Guangzhou Metro. It is reported that the shield method will be used again in some sections of Line 2 of the Guangzhou Metro.
NATM has also been widely adopted for construction of both running tunnels and stations in the Fuxingmen-Bawangfeng line of the Beijing Metro and Line 1 of the Guangzhou Metro in the 1980s and 1990s. NATM is still a most important principle used in the construction of metros on the mainland.
Cut+cover has increased for construction of metro stations in recent years, e.g. in the construction of three stations on Line 1 of the Shanghai Metro in the early 1990s and was later adopted for construction of the Fuxingmen-Bawangfeng Line of the Beijing Metro and Line 1 of the Guangzhou Metro.
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