Digital Tunnel and Its Application in an
Undersea Tunnel
Xiaojun Li
Lecturer, Department of Geotechnical Engineering,
Tongji University, Shanghai 200092, China
nelsontj@263.net
and
Hehua Zhu
Professor, Department of Geotechnical Engineering,
Tongji University, Shanghai 200092, China
zhuhehua@tongji.edu.cn
ABSTRACT
Digital Tunnel is a new concept in tunnel engineering. It is
an information system that provides information services
and innovative tools for the whole life cycle of tunnel
engineering. This paper first presents a framework of
Digital Tunnel. The framework includes data management
system of all relevant data in tunnel engineering, strata
modeling method and tunnel modeling method,
visualization tools, spatial analysis techniques and
engineering applications. Then an integrated platform of
Digital Tunnel is put forwarded. Finally, engineering
application study in Xia-men Xiang-an undersea tunnel,
which is the first undersea tunnel under construction in the
mainland of China, is provided. By integrating the data of
geological surveying, design, construction and monitoring
into the platform, and employing the modeling methods
proposed in this paper, a digital model of the tunnel is
established. The model is a real 3-dimensional one, and it is
very informative because data could be easily retrieved
through visualized way. Moreover, useful information
could be processed out of these data by innovative spatial
analysis tools. Results also show Digital Tunnel could also
be potentially very helpful in tunnel maintenance and
service management.
KEYWORDS: digital tunnel; undersea tunnel; digital
strata; spatial analysis; information system.
INTRODUCTION
Information technology (IT) changes almost every aspect of our lives. In recent
years, more and more information technology based efforts have contributed to
the underground construction works. Gutierrez et al. (2003) in Virginia Tech
initiated a research project AMADEUS (Adaptive Real-Time Geologic Mapping,
Analysis and Design of Underground Space) which exploits new IT technologies
such as digital imaging, data management, visualization and computation to
improve analysis, design and construction of underground excavations in rock.
Its major objectives are to design and implement an information technologybased system for real-time and adaptive engineering-geologic mapping, analysis,
and design of underground excavations in rock, and to enhance teaching efforts
to engineering geology, mining, rock mechanics and computer science.
An European Union EUREKA project - CITYGRID was initiated in 2004 and its
main objective is to develop a precise mapping of whole cities in form of digital
city-models. The city model could be used in noise protection, urban planning,
traffic, fire brigade, monument protection, tourism advertising, project
development, architecture, transport services and pipework plan.
An European “Technology Innovation in Underground Construction
(TUNCONSTRUCT)” research project that promotes the development and
implementation of technological innovation in underground construction started
from 2005. The main aspects of the project are the complete integration of all
processes into an Underground Construction Integrated Platform (UCIP). A
center part of this is the Underground Construction Information System (UCIS),
which allows instant access to all relevant data of a tunnel over the whole tunnel
life cycle, and to provide data to all partners of a tunnel project.
Soga et al. (2005) both form Univ. of Cambridge and Imperial College London
launch a research project ‘Smart infrastructure’. The main objective of this
research project is to develop generic wireless sensor networks that allow sharing
of equipment and communication tools for monitoring of multiple types of
infrastructures including tunnels, bridges and water supply systems.
Sagong et al. (2006) in Korea Railroad Research Institute developed a digital
tunnel face mapping system (DiTFAMS) using PDA and wireless Network. The
DiTFAMS can record the RMR and Q system parameters and approximate
sketch of joints pattern in the text and bitmap formats and compute the RMR and
Q values at the tunnel face. Once the collected data are transmitted to the main
server through the wireless network, the main PC sever classifies the text and
image data sent from the PDA.
An IT-based tunnelling risk management system (IT-TURISK) was also reported
by Yoo et al. (2006). IT-TURISK has been developed in a geographic
information system (ArcGIS) environment with a capability of performing
preliminary assessment of tunnelling induced third party impact on surrounding
environment.
In China, many tunnels of all categories and diameters are under construction and
still more tunnels will be built in future. In respect of complex tunnel projects in
difficult geological ground conditions, such information technology based efforts
are insufficient and inadequate.
In our opinion, Digital Tunnel is a package of effective and multi-purpose tools
for reducing the difficulties in the challenging tunnel projects. In fact, Digital
Tunnel is an information system that provides information services and
innovative tools for the whole tunnel life cycle. In the design stage, by
transforming the discrete strata data such as boreholes and planar design
drawings into continuous 3-dimensional digital form, it can serve as geological
and analysis tools for tunnel design. In the construction stage, by further
integrating construction information and monitoring data into the digital strata
and digital tunnel, it allows instant information access of all relevant data,
providing data management for tunnel construction. In the maintenance stage, by
retrieving data quickly and accurately through visualization and spatial analysis
tools, it can be very helpful to analyze the health status of the tunnel and identify
potential risks, thus improving maintenance efficiency. Finally, a Digital Tunnel
could be built in the computer system corresponding to the real one, therefore
providing valuable data and experiences for similar projects. In addition, the
Digital Tunnel can also be used for educational purposes.
In this paper, a framework of Digital Tunnel is presented at first. The framework
includes data management system, strata modeling method and tunnel modeling
method, visualization tools, spatial analysis techniques and engineering
applications. Then an integrated platform of Digital Tunnel is put forwarded.
Finally, engineering application study in Xia-men Xiang-an undersea tunnel,
which is the first undersea tunnel under construction in the mainland of China, is
provided.
A FRAMEWORK OF DIGITAL TUNNEL
In order to build a Digital Tunnel in the computer system corresponding to the
real one, a data management system where all of the relevant data resides should
be established at first. Then a 3-dimensional model comprised of environment,
strata and tunnel should be constructed respectively. By utilizing visualization
tools, then we can see a tunnel project in the computer system, and perform
visualized data queries by simple clicks. Furthermore, based on the 3dimensioanl model and the underlying data, spatial analysis tools could be
employed to make queries, reasoning, measurements and transformations on it,
therefore processing useful information out of these data. Finally, engineering
applications, such as tunnel monitoring data management system and integrated
numerical analysis program, could be developed in the framework, providing
information services and innovative tools for whole tunnel life cycle.
The framework of Digital Tunnel comprises five aspects, which are data
management, modeling methods, visualization, spatial analysis tools and
engineering applications, as shown in Figure 1.
Figure 1. The framework of Digital Tunnel
In the following section, data management and modeling methods will be
discussed at first. Then the architecture of an integrated platform is proposed, and
the platform is suggested to be built based upon current computer-aided design
(CAD) software to provide visualization for the Digital Tunnel. Spatial analysis
and engineering application will be introduced in the case study section.
Data management
Data taxonomy
The data management of tunnel engineering involves huge amount of data
ranging from geography, geological survey, tunnel design, tunnelling process,
monitoring, inspection, maintenance and much more. To integrate all of data into
the database systematically, a data taxonomy is established both from the
geological viewpoint and engineering viewpoint. The taxonomy is organized as a
hierarchy structure, with the items in first level stands for basic geography, basic
geology, engineering geology, hydrology, environmental geology and tunnel
respectively. Each item is further divided into child items which are the second
level items, and so forth. For example, basic geology is divided into areal
geology, bedrock geology, quaternary period geology and exploration etc.
Detailed taxonomy is too long to be listed here, Figure 2 illustrates the main
structure of the taxonomy.
To exchange the data and information and improve the efficiency of data
utilization, the taxonomy of each item is encoded into characters. For example, in
the first level, engineering geology is encoded as ‘C’. In its second level,
engineering geology prospecting is encoded as ‘CA’. Similarly, various
engineering geology prospecting methods such as borehole method and physical
prospecting method in the third level are encoded as ‘CAA’, ‘CAB’ and so on.
The classification code of each item is also shown in Figure 2.
Specifically, each third level item in the tunnel classification is encoded as a
number denoting tunnel design, construction, monitoring, inspection etc. For
example, the design and construction of NATM tunnel is encoded as ‘FA1’ and
‘FA2’ respectively. This encoding method provides a consistent third level
classification for different type of tunnels.
Figure 2. Taxonomy of Digital Tunnel data
Database design
The database design is an important step in architecting a database management
system. Among the huge amount of data involved in tunnel engineering, data that
describe the location and geometry of real world object are essential. These data
are called spatial information. Other data can be seen as the attributes of the real
world objects, therefore they can be associated with such objects. Such data are
called attribute information.
In the tunnel engineering, a complicated object usually can be decomposed to
elementary objects. For example, a ring for lining of shield tunnel is assembled
by segments, which could be seen as elementary objects. Similarly, tunnel is a
big object consisting of many child objects. Therefore, database is designed with
the concept of object. Object is described by tables. The tables comprise one
main table and several auxiliary tables. Spatial data and essential attribute data
are stored in the main table. The main table is indispensable. Nonessential
attribute data are stored in the auxiliary tables, so the auxiliary tables are
optional. A unique object identifier is used to link the main table with the
auxiliary data tables. Objects of same type are stored in one data table.
Database management system usually provides constraint tools for the table
design, such as primary key, foreign key and default value. Such constraints
could be employed to maintain the relations among the tables and improve the
efficiency for data accessing. Among them, the primary key constraint could be
used as the unique object identifier.
Taking the stratum data table design as an example, the stratum is described by
five data tables, which are stratum criterion table, standard stratum description
table, borehole information table, borehole stratum description table and whole
stratum characterization table. The design and relations between them are shown
in Figure 3.
The database design can be easily implemented by traditional database
management system, such as Microsoft SQL Server. It is also very flexible for
extending object information by simply introducing additional attribute data
tables. Moreover, it also can be adopted as a distributed data accessing and
storing scheme for large datasets when integrating all data into one database is
impossible from the viewpoint of data management.
Figure 3. data table design of strata information
strata and tunnel modeling
Strata modeling
Geological features are quite complicated in nature. Accordingly, numerous
commercial software packages such as MicroLynx, GOCAD are available for
building 3D geological models. Although these tools have proved to be very
successful in mining engineering and petroleum engineering, they are very time
consuming in practical applications due to enormous imperative manual
interactions. Therefore, it is desirable to develop a simple and robust 3D solid
modeling method that addresses the specific needs in tunnelling engineering
when alluvial system is a common geological environment. In the following
section, a solid modeling method of strata is proposed for such conditions.
In urban areas, borehole data is the main geological information. Based on
borehole data, a triangular prism modeling method is used to reconstruct the
strata. The main idea of this method is to connect the top points of all borehole
using 2-dimensional delaunay triangulating algorithm, and then extrude the
triangles vertically to create the triangular prisms, thus the strata entity is built.
The approach is described as follows:
(1) Creation of uniform strata layers in each borehole
Due to the variation nature of geological features, stratum layer information in
each borehole is often different with others. But for alluvial geological
environment, an uniformed strata layer sequence could be established by putting
all stratum information together. Then for each borehole, if a stratum is absent,
then a virtual one with zero thickness (except for the bottom stratum) will be
inserted into the borehole strata information, to ensure the strata layer sequence
information is conformed to each others. For examples, as shown in figure 4, the
stratum 1, 3 and 6 is absent in borehole j, so a zero thickness stratum 1 and 3 is
inserted into the borehole, and a virtual stratum 6 is appended with its thickness
equal to that of borehole i.
By this way all the boreholes will have an equal strata number and same strata
sequences.
(2) Constructing of 2-dimensional reference triangular mesh
According to the x, y coordinate of each borehole on the earth surface, a 2dimensional triangular mesh can be constructed by delaunay triangulation
algorithm. The mesh will be used as reference triangles for the strata solid
models in the next step.
Figure 4. Borehole data pre-processing
Figure 5 Triangular prism generated from boreholes
(3) Modeling of the final solid strata
The modeling of strata solids is illustrated in Figure 5. A triangle T(i, j, k) has
been created in the step 2, where i, j, k is the borehole number. Since the strata
number and strata sequence in each borehole is same, a triangular prism can
therefore be constructed through the points i1，j1，k1，i2，j2，k2, with its upper
surface is T(i1, j1, k1) and lower surface is T(i2, j2, k2). Other triangular prisms are
constructed along the boreholes in the same way, until it reaches the bottom of
the boreholes. Under the circumstances that the thickness of stratum in the three
boreholes is all zero, i.e. all of the three points are virtual stratum introduced in
the step 1, creation of the triangular prism is skipped. By iterating each of the
triangles and constructing triangular prisms through the boreholes, the whole
solid strata model can be built finally.
The strata modeling method described above is very intuitive, it is also easy to be
implemented. Although it may not be applicable for complex geological
conditions, it is suitable for simple geological environment such as urban areas
where strata is typically made up of alluvium. Another advantage of this
modeling method is that the strata can be constructed from boreholes without any
manual interactions, therefore providing a convenient tool for engineering
applications.
Tunnel modeling
Wireframe, boundary representation (B-rep) and constructive solid geometry
(CSG) are three popular ways of representing solids in computer-aided design.
Because of the complex nature of the geological entities, it is difficult to
represent strata by CSG method. We suggest using the B-rep as the tunnel
modeling method, so that it would be easier to combine the tunnel model with the
strata model.
Take the modeling of NATM tunnel as an example, the modeling process can be
described as three steps: construction of tunnel cross-section, representation of
tunnel axis curve and modeling of tunnel body. The cross-section of the tunnel
can be constructed by translating the cross-section design parameters into groups
of segments. The segments usually consist of straight line segments and circular
arc segments. Tunnel axis curve can be represented by transforming the planar
and longitudinal curve of the tunnel into a continuous curve in 3-dimensional
space. Then the tunnel body is modeled by extruding the outline of cross-section
along the tunnel axis curve. The combination of the strata and the tunnel can be
achieved by employing boolean operations between them. In computer-aided
software such AutoCAD, both the extrusion and boolean operation are its basic
functionality. Therefore, the modeling process can be finished within such
software environment.
The tunnelling construction process can also be represented in similar ways. For
example, the excavation of the tunnel can be simulated through boolean
operations between tunnel body and its excavation part.
An integrated platform of Digital Tunnel
An integrated platform is designed to provide a system for data management,
information services, modeling, visualization and spatial analysis tools of Digital
Tunnel. The system architecture of the platform is arranged in 3-tiers, as shown
in Figure 6.
Figure 6. System architecture of the platform
The first tier is a virtual data provider for the whole system, serving as objectoriented data warehouse where all of the spatial data and attribute data reside.
Users can access these data with no care about where they are and what are the
underlying structures of them.
The second tier is called business logic tier. Based on the unified data accessing
interface, it provides core functionalities such as strata modeling, tunnel
modeling, visualization, spatial analysis tools and engineering application
methods for various purposes. It is independent from the first tier in that such
functionalities are working on the unified data structure, not on the physical
database. Specifically, it can be further divided into four levels, which are
modeling level, visualization level, analysis level and application level
respectively.
The third tier is user-oriented services tier, providing graphics interface and
ready-to-use functionalities for final users.
It has been mentioned that the first tier is implemented on the basis of database
management system. And due to the 3-dimensional nature of the Digital Tunnel,
the second and the third tier of the platform should establish mainly on computeraided software environment, such as AutoCAD and other CAD software. In
addition, Internet browser based user interfaces are also important part of the
platform for users to access information services.
Data accessing tool
Although the database is designed with the concept of object, retrieving data of
objects from the database is not an easy task due to the fact that data often reside
in different tables and the database structure is complicated. A data accessing
tool is provided to simplify the process by packing data of objects automatically,
therefore providing object-oriented data accessing way for users while hiding
detailed structure of the database.
A static object description model provides as the basis of the data accessing tool.
The main idea of the model is that object table in the database holds a group of
objects of same type, object can be decomposed to attributes and child objects,
and child object can be integrated into parent object. The object description
model is organized as a hierarchy structure, as shown in Figure 7. Obviously, the
structure is compatible with the proposed database design scheme, and it can be
defined in the user’s program and/or stored in another database. Moreover,
metadata of the object can be implemented on this static description structure,
providing a standard for data exchanging.
Figure 7. The static object description model
A scheme for the inter-connecting of visualized object with database
In the digital platform, objects of same type are managed together as a collection,
namely ObjectCollection. By defining the static description structure of object
(see Figure 4) within the collection and using the data accessing tools mentioned
above, ObjectCollection is treated as a counterpart of tables of database. Data is
retrieved from database through the collection. Then objects are constructed by
the collection. By employing the modeling methods proposed above, the final 3dimensional strata and tunnel model could be constructed and then sent to the
graphics system for displaying. The graphics system may have an independent
data structure, for example GraphicsObject, for each visualized object. An
unique graphics identifier, namely GraphicsID, is assigned to each visualized
object (i.e. GraphicsObject). The GraphicsID is then served as a key mapped to
the original object. Finally, when user selects a visualized object in the graphics
system, the original object is identified through the GraphicsID, and the attribute
data about it can be retrieved through the ObjectCollection from the database.
The process is illustrated in Figure 8.
Figure 8. Modeling and information query process
ENGINEERING CASE STUDY OF XIA-MEN XIANG-AN
TUNNEL
Project general information
Xiang-an tunnel, the first undersea tunnel located in Fu-jian province of China
mainland, is a 3.76 mile (6.05 kilometer)-long road tunnel with 2.61 miles (4.2
kilometer) are beneath the sea, connecting Wu-tong district to Xiang-an district
of Xia-men city. It is constructed with one service tunnel and two main tunnels
for eastbound and westbound traffic. The budget of this project is about 3.2
billion RMB (about 410 million US$) and the tunnel is scheduled to be
constructed within 4 years.
Figure 9. Map of Xia-men city
Net width and height of the two main tunnels is 13.5m and 5.0m respectively,
with inner profile area is 122 m2. The service tunnel is 6.5m wide and 6m high,
with an overhaul vehicle pathway above and municipal pipelines beneath. The
three tunnels are connected by 17 cross tubes at intervals of approximately 300m,
within which 12 tubes for human cross passage and 5 tubes for vehicles. The
maximum depth of the tunnel is 76.55yds under the seafloor.
Figure 10. Cross-section of the tunnels
Geological conditions of the field are mostly granite materials. However, some
unfavorable area exists including intensely weathered rock layers in both
offshore, sand layers with great permeability in the shallow bank of Xiang-an
section, and several strongly weathered deep slots under the sea area.
Due to the significance and construction difficulties, a Digital Tunnel is
developed to provide information services for the project.
The digital model and information query
There are totally 70 boreholes conducted in geological prospecting. By using the
modeling method proposed in above section, the 3-dimensional strata model is
constructed. The engineering geological data is incorporated into the model, so
that we can query the geotechnical data of each stratum through clicking.
Moreover, the model could serve as a basis for the analysis of geological
conditions as well as for tunnel design, and for geological forecasting during
tunnel construction. For example, we can get the geological profile at arbitrary
location along the tunnel axis, as shown in Figure 11.
The 3-dimensional tunnel model is also established, as illustrated in Figure 12.
By the analysis of the spatial location of the tunnel relating to the rock mass, the
tunnel is rendered with different color, depicting rock quality grade around it.
Design information is also integrated into the tunnel model. The exact tunnel
design drawing at a specified location can be retrieved by a simple click on it, as
shown in Figure 12. Therefore, engineers could easily find and verify the tunnel
design according to the rock conditions.
Figure 11. 3-dimensional model of strata
Figure 12. 3-dimensional model of the tunnel
Construction and monitoring information can also be managed and visualized
through the digital model. As shown in Figure 13, the construction overview of
the tunnel at a certain time is illustrated. The tunnel is constructed using the New
Austrian Tunnelling Method (NATM). And it is advanced from both ends. The
excavation method of each tube is also illustrated. For example, the main tube is
excavated by cross diaphragm method, while the service tunnel is excavated by
upper and lower bench method. The spatial location between the tunnel and the
slightly weathered rock mass is also illustrated in the figure, providing a good
understanding of the surrounding rocks. Monitoring information is managed
through visualized way. A small red ball is displayed right above the location
where monitoring is undertaken. The red ball is then served as a selection
indicator of monitoring data. When clicking on it, the user can query the detailed
monitoring data of that section.
Figure 13. 3-dimensional view of construction process and monitoring data
CONCLUSIONS
With the rapid development of information technology, modeling and
visualization as well as querying and analysis of tunnel project data has been an
important research area. This paper has presented a new concept – Digital Tunnel
- for tunnel engineering. First, a framework of Digital Tunnel is put forwarded.
Then, based on the characteristics of data of tunnel engineering, data taxonomy is
established; database is designed with the concept of object. Strata modeling
method and tunnel modeling method are also introduced to build 3-dimensional
model of tunnel project. Consequently, an integrated platform of Digital Tunnel
is established.
The proposed Digital Tunnel concept has been applied and examined in the Xiamen Xiang-an undersea tunnel, which is the first undersea tunnel under
construction in the mainland of China. The 3-dimensional model of the strata and
tunnel is successfully constructed at first. Geological, tunnel design, construction
and monitoring information can be effectively retrieved through the digital
model. In addition, spatial analysis tools such as predicting geological profile at
any specified location, analyzing rock mass quality grade around the tunnel has
been developed, which can offer new information for the tunnel design and
construction. Therefore, Digital Tunnel is a very promising technology; it could
be used in many aspects of the tunnel engineering.
It should also be noted that Digital Tunnel is an ongoing research project.
Traditional analysis means, such as numerical analysis system, are under
developing within the framework. Engineering application is still in its infancy,
and more spatial analysis tools are needed to provide information services for the
whole life cycle of tunnel engineering.
ACKNOWLEDGEMENTS
This research has been supported by The National High Technology Research
and Development Program (863 Program) of China (Grant No. 2006AA11Z118,
No. 2006AA11Z102), Shanghai Municipal Science and Technology Commission
(Grant No. 052112010, No. 05dz05806). The financial support is gratefully
acknowledged.
The authors would also like to thank Vice General Manager Mr. C. Zeng and Dr.
J. B. Zhang in Road & Bridge Construction Investment Corporation of Xia-men,
they provide us all kinds of data we needed and give us valuable suggestions
about our research works.
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