Typical Underwater Tunnels in the Mainland of China and Related
State Key Laboratory of Shield Machine and Boring Technology, China Railway Tunnel Group Co., Ltd., Zhengzhou 450001, China
Received 31 May 2017
Revised 14 July 2017
Accepted 31 July 2017
Available online 8 December 2017
Drill and blast
In the past decades, many underwater tunnels have been constructed in the mainland of China, and great
progress has been made in related tunneling technologies. This paper presents the history and state of the
art of underwater tunnels in the mainland of China in terms of shield-bored tunnels, drill-and-blast tun-
nels, and immersed tunnels. Typical underwater tunnels of these types in the mainland of China are
described, along with innovative technologies regarding comprehensive geological prediction,
grouting-based consolidation, the design and construction of large cross-sectional tunnels with shallow
cover in weak strata, cutting tool replacement under limited drainage and reduced pressure conditions,
the detection and treatment of boulders, the construction of underwater tunnels in areas with high seis-
mic intensity, and the treatment of serious sedimentation in a foundation channel of immersed tunnels.
Some suggestions are made regarding the three potential great strait-crossing tunnels—the Qiongzhou
Strait-Crossing Tunnel, Bohai Strait-Crossing Tunnel, and Taiwan Strait-Crossing Tunnel—and issues
related to these great strait-crossing tunnels that need further study are proposed.
Ó2018 THE AUTHOR. Published by Elsevier LTD on behalf of Chinese Academy of Engineering and Higher
Education Press Limited Company. This is an open access article under the CC BY-NC-ND license (http://
China has 18000 km of land coastline and 14000 km of
sea island coastline. There are more than 11 000 islands in China,
of which 6536 have over 500 m
area each and 455 have resi-
dents . Due to the restraints caused by the numerous bays
and straits, the economic development in local areas is not very
balanced and the transportation cost is high. Furthermore, China
has many inland rivers, including 28 major rivers. Due to the
restraints caused by the rivers, the urbanization on both sides
of the rivers has been severely impacted. As China’s economy
develops, it is highly necessary to build ﬁxed links crossing such
rivers, lakes, and seas. Due to the fact that China has a large
population and a relatively small per capita land area, tunnels
have obvious advantages when such ﬁxed links are built. Accord-
ing to statistics, more than 100 tunnels have been built crossing
underneath rivers, lakes, and seas around the world in the 20th
2. History and the state of the art of underwater tunnels in the
mainland of China
2.1. Shield-bored tunnels
In May 1965, the construction of Dapu Road Tunnel crossing
Huangpu River began; this was the ﬁrst river-crossing tunnel in
the mainland of China. Dapu Road Tunnel is 2761 m long, with
over 600 m of its length passing under Huangpu River. The tunnel
was completed and put into operation in June 1971 (Fig. 1). Since
then, numerous shield-bored tunnels have been built to cross riv-
ers, lakes, and seas. These tunnels are used for subways, railways,
highways, water delivery, oil/gas supply, power supply, and so
forth. The diameter of these shield-bored tunnels ranges from
2.4 m to 15.6 m. For example, Shanghai Yangtze River Tunnel,
which is used for highways and subways, had the largest diameter
in the world at the time of its construction, and Shiziyang Tunnel is
used for the Guangzhou–Shenzhen–Hong Kong High-Speed
Railway, which operates at a speed of 350 kmh
. Most of these
shield-bored tunnels have twin tubes (with one ﬂoor or double
ﬂoors), although some shield-bored tunnels have only one tube
with double ﬂoors used for highways (such as Shangzhong Road
2095-8099/Ó2018 THE AUTHOR. Published by Elsevier LTD on behalf of Chinese Academy of Engineering and Higher Education Press Limited Company.
This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
E-mail address: firstname.lastname@example.org
Engineering 3 (2017) 871–879
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Tunnel in Shanghai). These shield-bored tunnels pass through
typical ground conditions, such as the soft strata of East China,
the boulder strata of Chengdu and Lanzhou, and the composite
ground of South China with its extreme strength changes and high
strength. Su’ai Tunnel, which is currently under construction, is a
sea-crossing shield-bored tunnel with great challenges.
2.2. Immersed tunnels
Yong River Underwater Tunnel in Ningbo was the ﬁrst
immersed tunnel used for trafﬁc in China; it has one tube with
six bidirectional lanes. The tunnel is 1019 m long, with an under-
water section that is 420 m long and consists of four 85 m
immersed tubes and one 80 m immersed tube. The immersed
tubes are 11.9 m wide. The construction of Yong River Underwater
Tunnel began in June 1987; the tunnel was completed and put into
operation at the end of September 1995. The construction of Pearl
River Tunnel in Guangzhou began in October 1990 and ended in
December 1993. This tunnel is 1380 m long and 33.4 m wide, with
an immersed section that consists of ﬁve immersed tubes with a
total length of 457 m. The tunnel has three tubes; the west two
tubes are used for bidirectional four-lane highways and the east
tube is used for a double-track subway. The immersed tubes are
composed of a reinforced concrete structure. Most of the immersed
tubes are transported and sunken by controlling the hauling cable
of the winch at the river banks, and are connected using water
pressure (Fig. 2). Since then, 11 immersed tunnels have been built
2.3. Underwater tunnels built by the drill-and-blast method
Xiang’an Tunnel in Xiamen was the ﬁrst subsea tunnel built by
the drill-and-blast method in China. The construction of the tunnel
began in September 2005, the tunnel was broken through in
November 2009, and the tunnel was put into operation on 26 April
2010 (Fig. 3). Since then, several underwater tunnels have been
built by the drill-and-blast method (Table 2).
2.4. Technologies for underwater tunnels in China
With the development of China’s economy and urbanization,
the rate of construction of underwater tunnels is increasing.
According to statistics, more than 100 underwater tunnels have
been built in China, and more than 20 underwater tunnels are
currently under construction in China. These underwater tunnels
are mainly constructed by the shield method, with 13 underwater
tunnels being constructed by the immersed tunnel method and
only three being constructed by the drill-and-blast method. Some
special underwater tunnels are constructed by the ‘‘drill-and-
blast plus shield method.”
Breakthroughs have been made in the following key technolo-
(1) Regarding underwater tunnels built by the drill-and-blast
method, comprehensive advanced geological prediction technol-
ogy has been developed, and advanced consolidation and radial
seepage-reducing and grouting technology have been innovated;
these provide solutions that allow underwater tunnels to cross
fault and fracture zones and weathered deep troughs, and ensure
construction safety. For urban underwater tunnels located in soft
surrounding rocks, a method to deﬁne the minimum overburden
under the prerequisite engineering measures has been established,
a deformation control standard based on the construction steps has
been determined, and an underwater interchange tunnel with a
span of 25 m, a cross-sectional area of 376 m
, and an overbur-
den/span ratio of 0.46 has been built.
(2) Regarding shield-bored tunnels, breakthroughs have been
achieved in the manufacturing and application of shields with
greater than 15 m diameter and in the technology of boring large
cross-sectional shields in soft/hard heterogeneous ground, ground
with weathered sphere-shaped granite, ground with large
Fig. 1. Dapu Road Tunnel in Shanghai.
Fig. 2. Transportation of an immersed tube by controlling the hauling cable of the
winch at the river bank.
Fig. 3. Xiang’an Tunnel in Xiamen.
872 K. Hong / Engineering 3 (2017) 871–879
boulders, ground with high water pressure (0.9 MPa), and so forth
. In addition, drainage-limited pressure-reduced cutting tool
replacement technology and shield docking technology have been
developed, and a technology to replace cutting tools under atmo-
spheric pressure has been innovated.
(3) Regarding immersed tunnels, technologies for pre-casting,
transporting, and sinking immersed tubes by means of mobile
dry docks have been developed; a technology to construct long
immersed tunnels under deep cover in the sea has been innovated;
and a large-scale immersed tunnel has been built to cross rivers
with high water level ﬂuctuations and high water ﬂow rates .
3. Typical underwater tunnels in the mainland of China
3.1. Xiang’an Tunnel in Xiamen
Xiang’an Tunnel in Xiamen is 6.05 km long, of which a 4.2 km
long section is located under the sea. The tunnel is bidirectional
and has six lanes; its use reduces the driving time from the Xiamen
Island to Xiang’an from the original 1.5 h down to 10 min.
The tunnel has three tubes: two main tunnel tubes and one ser-
vice tunnel tube in between. The excavation cross-sectional area of
the main tunnel tube reaches 170 m
; the service tunnel has a
repairing passage and an escape passage in its upper part and a
municipal utility gallery in its lower part. Two ventilation shafts,
as shown in Fig. 4, are installed at positions close to the sea, in
order to cope with the operation ventilation. A total of 12 connec-
tion passages are installed for the tunnel in order to facilitate
evacuation. Along the tunnel route, the maximum sea water depth
is 26.2 m, the minimum overburden in the sea is 28.4 m, and the
lowest point of the tunnel is located about 65 m below the sea
The tunnel is mainly located in slightly weathered rocks; how-
ever, the completely weathered or heavily weathered ground on
both banks, the permeable sand strata through which the tunnel
section below the shallow beach on the Xiang’an side passes, and
the completely weathered or heavily weathered deep troughs
(bags) in the sea section (as shown in Fig. 5) had a severe impact
on the construction of the tunnel. Therefore, for the tunnel section
below the beach, dewatering was performed both from outside the
tunnel and from inside the tunnel. For the tunnel section below the
sea, technical measures such as advanced geological prediction (as
shown in Fig. 6), advanced grouting for water stoppage, and con-
solidation along the perimeter of the tunnel were performed;
instead of full-face curtain grouting, perimetrical curtain grouting
and top heading grouting  were performed to dramatically
reduce the grouting and consolidation scope; and modiﬁed
equipment was used to dramatically improve the tunneling
Immersed tunnels in the mainland of China.
Number Tunnel Main structure Year of completion
1 Yong River Underwater Tunnel in Ningbo Bidirectional, six lanes in one tube 1995
2 Pearl River Tunnel in Guangzhou Bidirectional, four-lane highways and a double-track subway 1993
3 Changhong Tunnel in Ningbo Bidirectional, four lanes 2002
4 Waihuan Tunnel in Shanghai Bidirectional, eight lanes in three tubes 2003
5 Luntou–Bio Island Tunnel in Guangzhou Bidirectional, four lanes 2010
6 Bio Island–University City Tunnel in Guangzhou Bidirectional, four lanes 2010
7 Hai River Tunnel in Tianjin Bidirectional, six lanes 2011
8 Zhoutouzui Tunnel in Guangzhou Bidirectional, six lanes 2015
9 Dongping Tunnel in Foshan Bidirectional, six lanes and a double-track subway 2017
10 Shenjiamen Port Subsea Tunnel in Zhoushan Bidirectional passenger way 2014
11 Hong Kong–Zhuhai–Macao Link Tunnel Bidirectional, six lanes Under construction
12 Honggu Tunnel in Nanchang Bidirectional, six lanes 2017
13 Dalian Bay Subsea Tunnel Bidirectional, six lanes Under construction
Underwater tunnels built by the drill-and-blast method in the mainland of China.
Number Tunnel Main structure Year of completion
1 Xiang’an Tunnel in Xiamen Twin tubes with six lanes 2010
2 Jiaozhou Bay Subsea Tunnel in Qingdao Twin tubes with six lanes 2011
3 Liuyang River Tunnel on the Wuhan–Guangzhou High-Speed Railway Single tube, double-track railway tunnel 2009
4 Liuyang River Tunnel in Changsha Twin tubes with four lanes 2009
5 Yingpan Road Xiang River-Crossing Tunnel in Changsha Twin tubes with four lanes 2011
6 Jiaozhou Bay Subway Tunnel in Qingdao Single tube, double-track subway tunnel Under construction
7 Haicang Tunnel in Xiamen Twin tubes with six lanes Under construction
Fig. 4. (a) Plane sketch, ventilation shafts, and excavation method for Xiang’an Tunnel in Xiamen; (b) photograph of the construction site of Xiang’an Tunnel.
K. Hong / Engineering 3 (2017) 871–879 873
3.2. Yingpan Road Xiang River-Crossing Tunnel in Changsha
Starting at Xianjiahu Road in the west and ending at Yingpan
Road in the east, the main route of Yingpan Road Xiang River-
Crossing Tunnel in Changsha has a total length of 2850 m. The
main tunnel is bidirectional and has four lanes and a design speed
of 50 kmh
. Ramp A and Ramp B are on the west bank of the
tunnel and Ramp C and Ramp D are on the east bank. The ramps
have only one lane, with a 40 kmh
design speed; the total length
of the ramps is 2752.4 m. The tunnel was constructed by the drill-
and-blast method. Fig. 7 illustrates the layout of the tunnel. The
tunnel mainly passes through round gravel strata, completely
weathered or heavily weathered slate, and fresh backﬁlled soil.
The ground has strong permeability and poor self-support capabil-
ity and was subject to collapse and water inﬂow during excavation.
The tunnel crosses three fracture zones below the river (Fig. 7).
Because the overburden of the tunnel consists of sludge
strata, round gravel strata, and completely weathered or heavily
weathered slate, a minimum overburden design method based
on engineering measures was established, a deformation control
standard based on the construction steps was deﬁned, and tech-
nical measures such as forepoling, pipe roofs, sequential excava-
tion, and coordinated double-support layers were taken in order
to ensure the overall stability of the tunnel. In the end, an
underwater tunnel with a super-shallow overburden was suc-
cessfully built; the largest span of the tunnel is 25 m, the largest
excavation cross-sectional area is 376 m
, and the overburden/
span ratio is only 0.46. At the interchange point in the round
gravel strata, the four tunnel tubes have close spacing, with
the strata between the upper tunnel tube and the lower tunnel
tube being less than 0.5 m thick and the horizontal spacing
between the tunnel tubes being 2.8 m. To address this situation,
measures were taken such as excavating the lower tunnel tube
before the upper tunnel tube, performing construction activities
alternately, performing advance support, performing construction
activities step by step, and installing the lining in a timely man-
ner. To enable the underground interchange, the tunnel is
smoothly connected to the urban roads on both banks of the
3.3. Shiziyang Tunnel on the Guangzhou–Shenzhen–Hong Kong
Express Rail Link
Shiziyang Tunnel is located between Dongchong Station and
Humen Station on the Guangzhou–Shenzhen–Hong Kong Express
Rail Link. The tunnel is 10.8 km long, of which the shield-bored
Fig. 5. Geological proﬁle of Xiang’an Tunnel in Xiamen. F1, F2, and F3 are the completely weathered or heavily weathered deep troughs; F4 is the completely weathered or
heavily weathered deep bag.
Fig. 6. (a) Advanced geological prediction and advanced grouting; (b) photograph of the construction site. TSP: tunnel seismic prediction; GPR: ground-penetrating radar.
Fig. 7. (a) The plan layout and (b) the proﬁle of Yingpan Road Xiang River-Crossing Tunnel in Changsha.
874 K. Hong / Engineering 3 (2017) 871–879
section is 9340 m long. The inner diameter of the tunnel is 9.8 m
and the outer diameter is 10.8 m. The twin tubes of the tunnel have
23 connection passages. Shiziyang Tunnel is the ﬁrst underwater
high-speed railway tunnel with a design speed of 350 kmh
the world, and is also the ﬁrst super-long underwater tunnel in
China. The shield-bored section of Shiziyang Tunnel crosses under-
neath the Xiaohuli Channel, the Shazaili Channel, and the Shizi
Channel; the Shizi Channel is 26 m deep at its maximum and is
the main channel of Pearl River. The maximum cover of the tunnel
is 52.3 m and the minimum cover is 7.8 m. The minimum under-
water cover of the tunnel is 8.7 m deep, and the design water pres-
sure reaches 0.67 MPa.
Most of Shiziyang Tunnel is located in slightly weathered sand-
stone, sandy conglomerate, and sandy mudstone. The maximum
uniaxial compressive strength reaches 82.8 MPa, the content of
the quartz in the rock reaches 55.2%, and the maximum permeabil-
ity coefﬁcient of the ground reaches 6.4 10
. The geolog-
ical proﬁle of Shiziyang Tunnel is shown in Fig. 8 .
A cutting tool replacement technology for use under conditions
with reduced pressure and limited drainage was created during the
construction of the tunnel. In fractured ground with high perme-
ability, the water in the chamber is drained and the pressure in
the chamber is reduced—based on ﬂuid–structure interaction
theory—to stabilize the tunnel face by low air pressure in order
to enable workers to enter the chamber and perform operations
. The new technology had a signiﬁcant effect on the construction
of Shiziyang Tunnel, for which the pressure-reducing ratio reached
34.4%. A technology in which shield boring is performed from
opposite directions, with docking in the ground and shield disas-
sembling in the tunnel, was applied in the construction of the tun-
nel; the docking accuracy reached 28.5 mm deviation in the
horizontal direction and 19.6 mm in the vertical direction. The
docking effect is shown in Fig. 9 .
3.4. Water-delivery tunnel for the Taishan Nuclear Power Station
The water-delivery tunnel for the Taishan Nuclear Power Sta-
tion is located under the sea, between Yaoguzui (on land) and Dajin
Island. The tunnel is 4330.6 m long; its excavation diameter is 9.03
m, the cover of the tunnel ranges from 10 m to 29 m, and the dis-
tance between the twin tubes of the tunnel is 29.2 m. The tunnel
was constructed by means of slurry shields with air cushions,
and it is provided with secondary lining on the inner side of the
segment lining. The water outlet section of the water-delivery tun-
nel passes through Yanshanian (
5) granite, the water-intake sec-
tion of the water-delivery tunnel passes through silty sandstone of
the Laohutou Formation of the Devonian System (D2-31), and the
other sections of the water-delivery tunnel pass through coarse
gravelly sand and gravelly sandy clay. The most difﬁcult challenge
of the project was related to the slightly weathered granite, which
had a maximum strength of 197 MPa, and to the spherical weath-
ered granite boulders that occurred locally, as shown in Fig. 10.
A real-time kinematic (RTK) system, a high-frequency high-
density seismic wave technology, and a common-depth-point
(CDP) stacking technology were used for geophysical detection.
Fig. 8. Geological proﬁle of Shiziyang Tunnel.
Fig. 9. The docking effect used in the construction of Shiziyang Tunnel.
K. Hong / Engineering 3 (2017) 871–879 875
In addition, a technology that permits accurate detection of abrupt
bedrock protrusion and boulders under the sea was developed
[10,11]; this technology accurately determines the top surface of
the bedrock and the boulders. A fragmentation blasting technology
to determine the layer location and the operation depth below the
seabed was also developed [10,11]. Underwater ground blasting
was performed on the high-strength bedrock during the tunnel
construction [12,13]. After bedrock blasting, the diameter of the
cores was mostly below 30 cm, and only a few cores had a diame-
ter between 30 cm and 55 cm. With the assistance of these tech-
nologies, the shield machines successfully passed through the
200 m long bedrock section, as shown in Fig. 11.
4. Typical underwater tunnels under construction in China
4.1. Shiziyang Tunnel on the Foshan–Dongguan Intercity railway
Shiziyang Tunnel on the Foshan–Dongguan Intercity Railway is
an important control works on the east–west axis of the Pearl River
Delta Intercity Railway; this is the second underwater shield-bored
tunnel that crosses the Shizi Channel. The tunnel is 6.15 km long
and has an underwater tunnel section that is 1.8 km long. This
tunnel was built by means of the shield method. As shown in
Fig. 12, the shield machine bored for a length of 4.9 km in a single
The prominent characteristics of this project included high
water pressure and long-distance boring in soft/hard heteroge-
neous ground. The design water pressure reached 0.9 MPa, and
the difference between the hard ground and the soft ground in
the same cross-section of the tunnel reached 84.6 MPa. Such char-
acteristics caused major challenges for the shield boring machine
and for replacement of the cutting tool. A technology of full-face
disc cutter replacement under atmospheric conditions was
adopted for this project. As there is no opening within a scope of
4.8 m around the center of the cutterhead, clogging easily occurs
during shield boring. Therefore, a correlation between the boring
speed, ground characteristics, and cutterhead center ﬂushing was
established. When the cutterhead was under atmospheric condi-
tions, muck could only enter the slurry port after passing a distance
of 3.97 m; as a result, clogging and delayed discharging easily
occurred. Therefore, a complete set of shield boring control tech-
nologies was developed, which laid a technological foundation
for the construction of underwater shield-bored tunnels with
super-deep cover in China.
Fig. 10. (a) A sketch of the water-delivery tunnel for the Taishan Nuclear Power Station; (b) locally encountered spherical granite boulders.
Fig. 11. (a) Top surface of bedrock with three-dimensional graph showing accurate boulder location determination; (b) cores from the bedrock after blasting.
Fig. 12. A longitudinal proﬁle of Shiziyang Tunnel on the Foshan–Dongguan Intercity Railway.
876 K. Hong / Engineering 3 (2017) 871–879
4.2. Su’ai Tunnel in Shantou
Su’ai Tunnel in Shantou is located on the second line of National
Highway G324. The tunnel is bidirectional and has six lanes and
functions as part of an urban highway. The main line of the tunnel
has a design driving speed of 60 kmh
; the total length of the
project is 6.68 km, of which the tunnel is 5.3 km. The length of
the shield-bored tunnel is 3047.5 m, and the diameter of the
shield-bored tunnel is 14.5 m. Fig. 13 shows the plan layout of
Su’ai Tunnel is the ﬁrst subsea tunnel in China to be located in
an area with eight degrees of seismic intensity. The tunnel passes
through challenging ground, such as very soft soil, boulders, and
soft/hard heterogeneous ground in the same cross-section as
marine muddy soil (in the upper part of the excavation) and
granite with a strength of more than 216 MPa (in the lower part).
Seismic-resistant measures, seismic-reducing measures, and
seismic-isolating measures were innovatively used in the design
of this tunnel (as shown in Fig. 14). For example, a node structure
that can be adapted to serious deformation was used to dissipate
seismic-induced energy, and simultaneous grouting materials with
a strong compressive deformation capacity were used to achieve a
seismic-isolation effect. Protruding bedrock exists in local
positions, and there is very soft sandy clay in the upper part of
the tunnel cross-section. Therefore, abnormal damage could occur
to the cutting tools due to overloading during shield boring. To
address this issue, a technology was developed to trace the force
undertaking and operation of the cutting tools .
Su’ai Tunnel had complex geological conditions, great construc-
tion difﬁculties, and high risks, so its construction involved the use
of innovative technologies. The construction of Su’ai Tunnel pro-
vides a reference for the construction of other large-diameter sub-
sea shield-bored tunnels in China in the future.
4.3. Immersed tunnel on the Hong Kong–Zhuhai–Macao Bridge
The main project of the Hong Kong–Zhuhai–Macao Bridge is
29.6 km long, including a 22.9 km long bridge and a 6.7 km long
immersed tunnel. The immersed tunnel has six lanes and crosses
the west navigation channel of Lingding Channel and the Tonggu
navigation channel. An artiﬁcial island was established on each
end of the immersed tunnel. This immersed tunnel is the ﬁrst
immersed tunnel built in the sea in China, and is also the longest
and deepest immersed tunnel in the world. The immersed tubes
were installed 45 m below the seabed. Fig. 15 shows the plan
layout, island cofferdam, and immersed tube transportation for
the immersed tunnel of the Hong Kong–Zhuhai–Macao Bridge.
During the construction of the immersed tunnel, the following
innovative technologies were developed: a technology to build
large artiﬁcial islands in the sea, a technology to control and deal
with sedimentation in the immersed tube trenches located at the
sea entrance, a technology to fabricate the 180 m long reinforced
concrete immersed tubes, and a technology to transport the
immersed tubes, which weighed 80000 t each. Furthermore,
heavy-duty equipment was developed for the construction of
immersed tunnels in the sea. These new technologies boosted
the technological progress of immersed tunnel construction in
China. On 25 May 2017, the immersed tunnel of the Hong Kong–
Zhuhai–Macao Bridge achieved breakthrough.
Fig. 13. Plan layout of Su’ai Tunnel in Shantou.
Fig. 14. A longitudinal proﬁle of Su’ai Tunnel with a layout of the energy-dissipating and seismic-reducing nodes.
K. Hong / Engineering 3 (2017) 871–879 877
5. Suggestions regarding three great strait-crossing tunnels in
The Qiongzhou Strait-Crossing Tunnel and Bohai Strait-Crossing
Tunnel are critical projects on the Heilongjiang–Hainan railway
and highway corridor, and the Taiwan Strait-Crossing Tunnel is
an important link between the mainland and Taiwan of China.
The construction of these three great strait-crossing tunnels has
great signiﬁcance for China .
5.1. Qiongzhou Strait-Crossing Tunnel
The minimum width of the Qiongzhou Strait is 18.3 km, the
water depth ranges from 20 m to 117 m, and the ground within
the scope of 200 m below the seabed mainly consists of clay and
silt of the Tertiary and Quaternary Periods, as well as sand strata
and sandy gravel strata. According to studies that were performed
on three possible routes—the east route, central route, and west
route—the central route is believed to be the most preferable
route; this route can be constructed by means of shield machine
Due to the ecological environmental protection situation in Hai-
nan Province, it is not suitable for numerous cars to come to Hai-
nan Province through a strait-crossing tunnel. Rather, the strait-
crossing tunnel should take the form of a railway tunnel for pas-
senger and freight transportation, with cars being transported by
train just as they are through the Channel Tunnel. Based on oper-
ational experience of tunnels with lengths over 20 km, both in
China and abroad, the railway tunnel may take the form of twin
tubes, as shown in Fig. 16. The tunnel will have characteristics such
as deep cover and high water pressure, so shield machines with the
capability to replace cutting tools under atmospheric pressure
should be used. Given the performance and lifetime of shield
machines, four shield machines may be used to bore the twin tun-
nel tubes from opposite directions; these can be docked in the
ground. The freezing of the ground at the docking points will be
a technological challenge and critical issue for this project.
5.2. Bohai Strait-Crossing Tunnel
The Bohai Strait-Crossing Tunnel will be located on the shortest
corridor from Northeast China to East China and South China. Lao-
tieshan Channel is an important sea navigation channel, so a bridge
cannot be built across it. The width of Laotieshan Channel reaches
50 km, so a highway tunnel cannot be built because the problems
of ventilation, disaster prevention, and emergency rescue cannot
be solved at present. Therefore, a ﬁxed railway link may be prefer-
entially considered in the short term, although the route of the
ﬁxed highway link should be preserved. Fig. 17 shows the geo-
graphical location of the Bohai Strait-Crossing Tunnel.
The route of the Bohai Strait-Crossing Tunnel crosses many
islands; this allows the long tunnel to be divided into several sec-
tions, is favorable for ventilation during construction and opera-
tion, and is favorable for emergency rescue. Considering the
requirements of emergency rescue and emergency evacuation,
the tunnel may consist of three parallel tubes, with the central tube
serving as an emergency rescue passage (as shown in Fig. 18). Due
to the thick cover of the tunnel, the tunnel will be mostly located in
bedrock. The surrounding rock of the tunnel will mostly be granite.
The tunnel may be constructed by tunnel-boring machines (TBMs)
with about 10 m diameter, assisted by drill and blast . How-
ever, the 25 km long single-direction boring of a TBM under marine
water is a major challenge.
Fig. 15. (a) Plan layout for the immersed tunnel of the Hong Kong–Zhuhai–Macao Bridge; (b) island cofferdam; (c) immersed tube transportation.
Fig. 16. A possible conformation for the Qiongzhou Strait-Crossing Tunnel: a
railway tunnel consisting of twin single-track tubes. Fig. 17. Geographical location of the Bohai Strait-Crossing Tunnel.
878 K. Hong / Engineering 3 (2017) 871–879
5.3. Taiwan Strait-Crossing Tunnel
The Taiwan Strait-Crossing Tunnel needs to cross the Taiwan
Strait over a width of more than 100 km. The water of the Taiwan
Strait is about 85 m deep, and the ground below the water is
mainly composed of interbed consisting of Tertiary sandstone
and shale of different thicknesses. The thickness of the sub-
horizontal sandstone and shale ranges from 200 m to 300 m. At
present, the optimal option may be to build a railway tunnel,
which may be constructed by open TBM assisted by the drill-
and-blast method .
According to the long-term prospective, and considering the
foresight and feasibility of the project, the Taiwan Strait-Crossing
Tunnel may consist of four railway tracks (of which two tracks
are used for trains carrying cars) to separate the freight transporta-
tion from the passenger transportation.
As noted earlier, many natural islands are present along the
route of the Bohai Strait-Crossing Tunnel, which can be used for
tunnel construction. However, there is no natural island along
the route of the Taiwan Strait-Crossing Tunnel; as a result, this pro-
ject presents signiﬁcantly greater difﬁculties. The difﬁculties of the
Taiwan Strait-Crossing Tunnel include the following issues: ①
How to build a working platform in the deep sea, so as to divide
the long tunnel into several sections; and ②how to guarantee
operational safety, protection, and emergency rescue in a subsea
tunnel that is more than 100 km long.
6. Conclusions and suggestions
In the past three decades, Chinese engineers have accumulated
a considerable amount of underwater tunnel construction experi-
ence, mastered a complete set of long underwater tunnel construc-
tion technologies, and established a strong technological basis and
great innovative capability. We now have the technological capa-
bility to build underwater tunnels for almost any purpose under
complex geological conditions and complex environmental
In order to further control the construction risks and project
investment of underwater tunnels, and to ensure the operational
safety of underwater tunnels, we propose that an offshore deep-
water operation shaft platform be studied, that the study of the
geological investigation technology for underwater tunnels be
strengthened, that the study of the rapid and safe long-distance
driving of underwater tunnels from a single portal be intensiﬁed,
and that the operational risk-control technology, ventilation, and
energy-saving technology of underwater tunnels be enhanced.
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Fig. 18. A possible conformation for the Bohai Strait-Crossing Tunnel, consisting of three parallel tubes.
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