Feasibility Study On The Submerged Floating Tunnel
Feasibility Study On The Submerged Floating Tunnel
Feasibility Study On The Submerged Floating Tunnel
4-11
10.2478/pomr-2018-0066
Bolin Jiang 1, 2
Bo Liang2
Shanshan Wu3
1 Chongqing Vocational Institute of Engineering, Chongqing, China
2 College of Civil Engineering, Chongqing Jiaotong University, Chongqing, China
3 Chonging Vocational College of Public Transportation, Chongqing, China
ABSTRACT
Abstract: Currently, one of the challenging tasks for Chinese engineering community is to construct a water-way
crossing of Qiongzhou Strait in the south of China. This project has also gained significant attention from researchers
in academia. The study presented herein is centered on providing a feasible solution for ac-complishing the above
mentioned task. Initially, different alternatives as the best location, judged on the basis of the environmental constraints,
are studied. Then the comparison between various structural solutions such as suspension bridge, submarine tunnel and
SFT is presented. Among these solutions, SFT appears to be a very suitable alternative for Qiongzhou Strait waterway
crossing due to distinctive advantages, like shorter distance, lower cost, less impact on environment and navigation,
etc. Based on the appropriate conception for cross sections, support systems, materials, joints and connection schemes,
a numerical model is developed by means of the FEM software ANSYS/Fluent. It is then analyzed under the influence
of different environmental loading conditions, varying the wave heights and lengths, current velocities and water
depths, which are typical in Qiongzhou Strait. The numerical results reveal that the proposed SFT solution performs
safely even under extreme weather conditions.
Keywords: Submerged Floating Tunnel, Qiongzhou Strait, waterway crossing, design features, numerical analysis
INTRODUCTION Strait waterway crossing, and relevant research about this topic
still keeps going even up to now. Tan et al. (2001) investigated
In the last two decades, several proposals for waterway the feasibility to construct an undersea tunnel by means of the
crossing have been carried out in China due to the demand of shield method for Qiongzhou Strait waterway crossing. Mai
traffic and development of civil engineering technology. For et al. (2003) analyzed the feasibility SFT in the Qiongzhou
example, crossings of Bohai Strait, Taiwan Strait, and Qiongzhou Strait in view of the environmental conditions, design schemes,
Strait are frequently discussed at present. On the other hand, the construction, and cost. Li et al. (2009) studied the feasibility
successful experiences of such waterway projects as Hangzhou to design a cable-stayed submerged floating tunnel in the
Bay Bridge, Qingdao Jiaozhou Bay Submarine Tunnel, Xiamen Qiongzhou Strait. Yan et al. (2015) provided several proposals
Xiang’an Submarine Tunnel, and Hong Kong-Zhuhai-Macau for SFT schemes in Qiongzhou Strait. Wu et al. (2016) studied
Bridge have greatly increased the enthusiasm and confidence on the significant aspects for type selection of SFT in the
to make true the dreams. Qiongzhou Strait.
Qiongzhou Strait is located in the south of China, between In this article, the environmental conditions of Qiongzhou
Leizhou Peninsula and Hainan Island. Since 1980s, the local Strait are introduced firstly, including the alternatives of
government started to investigate the feasibility for a Qiongzhou locations and solutions for crossing. Analyzed next are the
GENERAL CONDITIONS
OF QIONGZHOU STRAIT
Fig. 1. Proposed lines for Qiongzhou Strait crossing
GEOLOGICAL AND WEATHER CONDITION The Central Line. Straight line with a short waterway
crossing distance, connected conveniently with the existing
The Qiongzhou Strait is one of the largest three straits in highways and railways at both shores. The main advantages
China. Its geological and weather conditions can be summarized of this line include low investment for both the main and lead
briefly as following. projects, shorter travel time, and low operation cost. Therefore,
The length is about 80 kilometers from east to west, and the it can well meet the requirements of the city planning. One
width ranges from 18 to 35.5 kilometers (29.5 km on average) fact should not be denied, however, which is the maximum
from north to south. Its seabed is generally wide and deep, with water depth of 88 meters in this location.
the water depth ranging from 80 meters to 120 meters along The West Line. Compared with the other lines, its seabed
the central axis. In addition, scraps with a maximum height of is more flat, as the maximum water depth is only 55 meters,
70 meters and a maximum slope angle of 22°–24° are located but the distance of waterway crossing is larger. It is farther
on the south and north shores. away from the existing highways and railways at both shores,
Fractures are the major geological structure. The submarine so the investment for the main project and lead projects will
strata are mainly sedimentary shaped in the Tertiary and increase. In addition, this line has to avoid crossing the
Quaternary Periods. The upper layer is filled with sludge, sandy nature reserve in this area, which may cause more obstacles
clay or silt, and thick-bedded clay and silty sand are distributed in construction.
on bottom layer with thickness of hundreds meters. Among the three lines, the central line is the most appropriate
According to statistics, about ten ruinous earthquakes have location for the waterway crossing due to its shorter distance
occurred in this area, nine of which are over 6.0 in magnitude. and better geological conditions compared with the others.
The most serious earthquake occurred in the year of 1605 with Therefore the central line is selected in this article, and the
a magnitude of 7.5. All of them are shallow earthquakes with studies hereafter are based on this location.
the majority depth of focus ranging from 5 to 20 kilometers.
Besides, there is no records about volcano in this area. Alternatives of solution
The average annual temperature is 24°C. From May to On the central line location, some solutions for crossing are
October is the rainy season, and the average annual precipitation proposed. In general, they can be summarized as in Figure 2.
is more than 1500 ml. From May to November is the typhoon
season of the Qiongzhou Strait, especially in September.
Alternatives of location
According to careful investigations and evaluations, several
proposals of locations for waterway crossing in Qiongzhou
Strait are put forward by some researchers. In general, they
can fall into three lines: the east line, the central line, and the Fig. 2. Alternatives of solution: 1) Suspension bridge;
west line, as shown in Figure 1. 2) Submerged Floating Tunnel; 3) Submarine tunnel
The East Line. The location is characterized by the complex
topography, large water depth, and high risk of earthquakes. Of all types of bridges, suspension bridge is the longest in
Because the connection point of this line on Hainan Island is span. Thus a suspension bridge is a good solution of all bridge
far away from Haikou, the capital city of Hainan Province, it is alternatives, especially in dealing with long-distance waterways.
inconsistent with the development plans of this city. It would A Submerged Floating Tunnel (SFT) is an innovative underwater
bring more disadvantages than advantages to the city and even structure, applied for waterway crossing in particular case of
the province if constructed as proposed. long distances. Submarine tunnels include immersed tunnels
COMPARISONS AMONG
SOLUTIONS
BRIDGE
Advantages
Advanced technology of design and construction
The hydrological, meteorological, geological and
navigational conditions of the Qiongzhou Strait are
complicated, and therefore it is difficult to construct a bridge
in the large-depth zone. At present, the longest span of
Fig. 3. Relationship between height of tower and critical length
suspension bridges is found in the Akashi Bridge, whose
main span reaches 1,991 meters. China has rich experience
in construction of long-span bridges, such as the Zhoushan
Xihoumen Bridge (1,650 meters, 2009), the Runyang Yangtze Figure 3 shows that if HSS is selected for the cable material,
River Bridge (1,490 meters, 2005), and the Jiangyin Yangtze when the single span reaches 5,000 meters, the height of the
River Bridge (1,385 meters, 1999). In the central line location main tower will exceed 1,000 meters. In this case, the tower
aforementioned, it is feasible to construct a multiple spans will become the tallest of its type in the world. For this reason,
bridge with a single span of over 1,000 meters. Although the the design and construction of the foundation would be very
construction of piles is very difficult, the problems can be complicated, but the current technology and economy can
solved by means of updated construction technology. hardly support such a height.
Better traffic conditions Affected by weather
Compared with tunnels, it is undoubtedly much better The Qiongzhou Strait is located in a tropical area which
in lighting, ventilation, vision, comfort and so on when the is subject to the tropical monsoon climate. Every year, the
vehicles are running on the bridge. period from May to November is typhoon season. Every year,
Easier and more economical maintenance in particular, there are more than 5 days in September when
After operation for public transportation, the bridge requires the wind force is stronger than Level 8. Besides, there are more
less expense on lighting and ventilation compared with tunnels. than 24 days with dense fog on average every year. Because
In addition, the bridge is easier for maintenance service. the bridge is directly exposed to the natural environment, the
traffic condition is affected largely by weather conditions. In
Disadvantages case of strong wind, heavy fog, or other inclement weather
Higher expense of construction conditions, the safety of vehicles would be reduced inevitably,
The central line is around 20 km in length. If the bridge or what’s worse, the traffic will be interrupted due to serious
is designed with single spans for about 1,000 meters, it will weather conditions.
need about 20 piles and foundations. The average water depth Impact on surroundings and navigation
is over 50 meters, so it is more difficult to construct the piers The Qiongzhou Strait is a busy sea crossing. If the bridge
and foundations in these areas, and the cost is high. On the proposal is accepted, the piers of the bridge will have impact
other hand, the height of the main tower of the bridge will on the navigation of ships. In addition, the height from the
increase as the length of single span extends. deck to the water surface will limit big ships from crossing
The critical length of spans can be estimated under different the strait. Moreover, the tall main tower resulting from the
materials of cables. If only the self-weight of cables is taken long-span bridge will affect flights.
into account, the relationship between the critical length of Security during war time
span (Lc) and the height of the main tower (h) is obtained as The bridge project will be the most effective and convenient
in Figure 3. in connecting China Mainland and the Hainan Island when
HSS: High strength steel (Density: 7850 kg/m3; Elastic open to the public. Hence the security of this kind of huge
modules: 1000 MPa) projects should be considered at the beginning phase of
LSS: Low strength steel (Density: 7850 kg/m3; Elastic design. If war should happen one day, this bridge would be
modules: 300 MPa) destroyed soon by the enemy. Moreover, it is also an easy target
FRP: Fiber reinforced polymer (Density: 1800 kg/m3; Elastic of terrorist attacks even during peace time.
modules: 290 MPa)
CROSS-SECTION
°
45°
64
According to the clearance space requirements for traffic
lanes in the Code for Design of Road Tunnel (JTG D70-2004, in
Chinese), we combine the above-mentioned considerations and
Fig. 6. Proposed inclined configuration of cables
propose the following circular cross-section with dimension
(external diameter: 14.0 m, internal diameter: 12.0 m) as MATERIALS
illustrated in Figure 5.
The appropriate selection of materials is one important
14.0 m decision for any projects, the design and execution of the SFT
12.0 m in particular. On the other hand, the marine structures have
distinctive requirements for the materials.
Reinforced concrete is used widely in maritime structures
and particularly recommended when a large structural weight
is required to stabilize the structure. It can be used to contribute
to the structural strength and stiffness, as well as to provide
the weight needed to counteract the tunnel buoyancy. Bring
references from Immersed Tunnel, reinforced concrete can be
proposed for tube material of SFT, but the SFT structure must
be guaranteed to have the excellent capacity of water-proof via
0.5 m
tension forces, and steel strands can provide high strength and
high resistance to corrosion and fatigue.
vertical, horizontal, or tensional displacements, which depends Water Surface Water Surface
H1
The SFT is to be suspended in the water and can be subjected 100m
14.0m
bending planes. In this case, rigid inter-module joints are more
Current
suitable than flexible ones. In addition, the axial displacements 25m 50m 25m
H2
are allowable at the terminal joints due to thermal variations
and triaxial rotations (Martire, 2010). Therefore, rigid joints are
proposed for the inter-module joints of the Qiongzhou Strait SFT. Fig. 7. Geometry of numerical model
The connection between the SFT and the shore requires
appropriate interface elements to couple the flexible water Tab. 1. Regulations of tunnel longitudinal gradients
tunnel with the much more rigid tunnel bored underground. specified in different codes (Zhang et al. 2013)
This connection should be able to restrain tube movements, Parameters Values Units
without any unsustainable increase in stresses. Furthermore,
the joints must be watertight. In particular, the Qiongzhou Density of tunnel 2500 Kg/m3
Strait is located on the seismic area, so the risk of submarine Elastic modules of tunnel 32x103 MPa
landslides needs additional attention.
Moreover, the longitudinal gradients of the underwater Density of cable 7850 Kg/m3
tunnel should be taken into account. Because the SFT should
Elastic modules of cable 201x103 MPa
keep straight on the longitudinal direction, the longitudinal
gradients cannot be ignored. The length of the bored tunnel is Diameter of cable 0.3 m
closely related to the cost of the entire project, so it should be
implemented by appropriate gradients. From the regulations Density of Fluid 1028 Kg/m3
of longitudinal gradients specified in different codes as shown
in Table 1 (Zhang et al. 2013), the longitudinal gradients of The numerical model is implemented by means of the FEM
a bored tunnel are proposed to range from 0.3% to 3%. The software ANSYS/Fluent, in which process the Airy wave and
aim of the variable gradients is to connect the two smoothly RNG k – ε viscous mode are applied for simulating the wave and
and reduce the entire length. turbulence, respectively. Only displacement and rotation along
direction Z are restrained at both ends of the tube. Spherical
hinges have been assumed at both ends of the cables. In order to
Tab. 1. Regulations of tunnel longitudinal gradients
specified in different codes (Zhang et al. 2013) reproduce the full turbulent phenomenon in the water volume,
the distance from the inlet upstream side has been assumed
Codes Tunnel longitudinal gradients equal to 3D (D width of the polygonal section = 32.3 meters).
P.R China (MOT. JTG Likewise, a distance of 10D has been set so as to fully reproduce
0.3%–3%, maximum 4% depends on traffic
D70-2004 Code for conditions the wake turbulence that takes place downstream the tunnel. The
design of road tunnel)
width along direction Z is set to 100 meters, and so is the length
European Union Normal is less than 5%, it needs assistant of tube. The depth of the entire fluid volume varies depending
(DIRECTIVE 2004/54/ measures between 3% and 5%. on the location of the proposed SFT. The hexahedron elements
EC)
are applied for meshing the fluid and tube.
United States
(FHWA Road Tunnel) Recommended less than 3%–4% Concerning traffic loads, only motorway traffic loads are
considered in this numerical model. According to the Chinese
Great Britain code (MOT. JTG D70-2004 Code for design of road tunnels),
Depends on traffic and ventilation
(Design code for Road requirements, should be less than 6% the traffic loads are defined as distributed loads of 10.1 kN/m2.
and Bridge)
Norway To investigate the variable loading conditions subjected to
Maximum gradient depends on traffic,
(NPRA Motorway normal between 6%–8% the SFT, different cases are adopted:
Tunnel)
1) Different water depths. In Figure 7, H1 is fixed as 30 meters,
Sweden Normal less than 5%, it can be increased in while H2 is changed for 40 meters, 30 meters, and 20 meters
(VV Tunnel 2004) short distance permitted by experts according to different geological conditions of the seabed;
2) Different wave loads. According to the monitoring data in
Netherlands Design speed 90 km/h, less than 4%;
(SATO) design speed 120 km/h, less than 3%. the Qiongzhou Strait, the extreme wave loads are selected.
The extreme wave conditions include:
Return period of 20 years: Wave height 7.0 meters, Wave
NUMERICAL ANALYSES length 115.11 meters.
Return period of 25 years: Wave height 7.3 meters, Wave
On the basis of the aforementioned design aspects, the length 119.45 meters.
numerical model scheme is created as in Figure 7, with some Return period of 100 years: Wave height 8.6 meters, Wave
basic parameters selected from Table 2. length 137.38 meters.
ACKNOWLEDGEMENT
REFERENCES
CONCLUSIVE REMARKS 5. Yan H., Yang G., Yu J. 2015. The Lectotype Study on the
Submerged Floating Tunnel. Construction Technology, 44(7):
This article presents the preliminary feasibility studies on 113–116.
a Submerged Floating Tunnel (SFT) for the Qiongzhou Strait
waterway crossing. 6. Mazzolani F. M., Landolfo R., Faggiano B., Esposto M.,
According to the comparisons with a suspension bridge and Perotti F., Barbella G. 2008. Structural analyses of Submerged
a submarine tunnel, the SFT is selected as a better solution due Floating Tunnel prototype in Qiandao Lake (PR of China).
to its distinctive advantages, such as shorter distance, lower cost, Advances in Structural Engineering, 11(4): 923–938.