Development of an IT-based Monitoring System for ... - CiteSeerX

th

The 12 International Conference of International Association for Computer Methods and Advances in Geomechanics (IACMAG) 1-6 October, 2008 Goa, India

Development of an IT-based Monitoring System for Mountain Tunnel Construction Xiaojun Li, Zhigang Li, Wenqi Ding, Hehua Zhu Dept. of Geotechnical Engineering, Tongji University, Shanghai, China

Keywords: mountain tunnel, construction, monitoring system, alarming system, alarming value ABSTRACT: This paper presents the development and implementation of an IT-based mountain tunnel construction monitoring system. The main objective of the system is to establish an environment where the monitoring information of mountain tunnel construction is disseminated and managed through Internet. An Internet-based system architecture is discussed at first, and then a monitoring section, monitoring line and monitoring point organization scheme of monitoring data is introduced. To ensure the safety of tunnel construction, an alarming system consisted of five alarming levels is then proposed. Empirical alarming values of subsidence of tunnel crown and convergence deformation of tunnel outline are derived based on actual observation values of investigated project. Main characteristics of the system also include: (1) the capability to manage multiple tunnels at the same time, (2) the capability to customize monitoring sections and monitoring items; (3) 3D visualization of the monitoring results. As demonstrated in this paper, the system can helps to meet demands of improved safety and increased efficiency of the mountain tunnel construction.

1 Introduction Mountain tunnel construction is gradually increasing due to the development and upgrade of infrastructures in China. According to characteristic of mountain tunnel engineering, geotechnical monitoring technology has become the bridge between engineering theory and practice. Generally, geotechnical monitoring technology has an important impact on tunnel engineering excavation; it is also a main way to ensure tunnel safety in excavation and construction (e.g., Ye and Wang, 2004; Kavvadas, 2005; Kwon et al., 2006). However, traditional manual data acquisition and data processing methods were not effective in preventing site failures due to their inherent real time limitations. On the other hand, the development of centralized database of monitoring data, and utilization of advanced network technology make it possible to update the traditional work of tunnel monitoring. Therefore, tunnel monitoring information system and digital efforts have been a research focus of related works (e.g., Li and Zhu, 2002; Ackermann and Hunt, 2004; Chung et al., 2006; Wang et al. 2006). With the support of advanced IT technologies, this paper presents an IT-based tunnel monitoring system whose emphases are focused on the Internet-based architecture, management of monitoring data, visualization of monitoring data and alarming system for improved safety. Using the presented system, monitoring data from the instruments were stored in the central monitoring office, and simultaneously transmitted to the engineer and contractor through the Internet. Semi-automated database systems were used by the site staff to plot and interpret the data, and the results are also distributed through the Internet immediately. In addition, by introducing a five level alarming system and providing empirical alarming values against potential collapse, the system gives the client an important tool to perform risk management of tunnel construction.

2 Development of an IT-based tunnel monitoring system 2.1

System architecture

The main objective of IT-based tunnel monitoring system is to provide management, visualization and analysis tools of monitoring data for on-site staff and off-site stakeholders. Acquisition of monitoring data, data processing and analysis must be quick and efficient. Monitoring results should be distributed to engineers on time. For contractors and owners of the whole project, the tunnel monitoring system should provide the capability and flexibility to manage multiple construction sites. To meet such demands, a tunnel monitoring system with inherent support of network capability and great

1952

flexibility should be provided. The architecture of IT-based tunnel monitoring system is shown in Figure 1. The system consists of three modules: user access control module, database maintenance module and data processing module. Data processing module provides core functionality, such as data input, data analysis, visualization, forecast and alarming. The important characteristic of the system is the whole data process is completed through Internet. For example, raw data obtained inside tunnel are inputted into the system through web page by site staff. Data are stored in the central monitoring office. Engineer, contractor and owner then can get the latest information about the project and analyze the monitoring data through Internet no matter where they are. Another distinct feature of the system is its ability to customize multiple construction sites and monitoring items in each construction site.

Figure 1. Architecture of the IT-based tunnel monitoring system

2.2

Organization of monitoring data

Enormous data are produced in the process of tunnel monitoring. However, these data can barely be useful without basic tunnel information and construction information. Moreover, monitoring items inside tunnel keep changing with the advancing of tunnel working face. Monitoring items can also be altered according to variation of geological conditions and requirement of tunnel construction. To meet such requirements, data are classified into three categories: tunnel basic information, tunnel construction information and tunnel monitoring data. Tunnel monitoring data are further organized by monitoring cross sections. Each monitoring cross section consists of several monitoring lines, and each monitoring line consists of multiple monitoring points, as shown in Figure 2.

Figure 2. Organization of monitoring data Tunnel monitoring cross sections can be configured and altered along the tunnel advancing directions. Monitoring lines and monitoring items in a cross section can also be configured. Configuration templates of monitoring items in a cross section can be provided according to different rock conditions, as shown in Figure 3.

1953

Figure 3. Configuration of a monitoring cross section Monitoring data are organized either as a single monitoring point or as a monitoring line comprised of multiple monitoring points. These data include measurements of displacement, stress and strain of ground and structures, e.g., convergence deformation of tunnel outline, vertical subsidence at tunnel crown, displacement of slope at entrance of tunnel, ground displacement in the vicinity of tunnel, internal force of steel lattice girder, stress/strain state of final support, axial force of rock bolts and ground pressure on structures.

2.3

Visualization of monitoring data

The observed value of monitoring item versus time curve is an important form of visualization of monitoring data. Moreover, by combining with a 3D view of the tunnel and location of the monitoring items, these curves can be more informative and therefore more useful. As illustrated in Figure 4, a small sphere is displayed right above the location where monitoring is undertaken. The sphere is also served as a selection indicator of the monitoring data. When clicking on it, users can query the detailed monitoring data of the section.

Figure 4. Visualization of monitoring data

2.4

Alarming values

A main objective of monitoring in mountain tunnel construction is to prevent potential site failure and ensure tunnel safety in construction. When the subsidence of tunnel crown or convergence deformation of tunnel outline exceeds certain limits, ground in the vicinity of the tunnel becomes unstable and the support system must be reinforced to prevent potential collapse. Therefore, defining an alarming deformation value is an important task for tunnel construction monitoring. Besides, when the actual deformation value reaches or exceeds the alarming value, corresponding measures should be given beforehand. An alarming system consisted of five alarming levels is proposed for mountain tunnel construction, as shown in Table 1. The alarming values will be discussed further in the following section.

1954

Table 1. An alarming system consisted of five alarming levels Alarming level

Monitoring value divided by alarming value

I

50%

II

80%

III

100%

IV

150%

V

>=200%

Phenomenon

Corresponding measures

The excavation face is stable, and there is no crack in the sprayed concrete lining. There are local cracks in the sprayed concrete lining, water percolates from the cracks. Deformation of the ground tends to be stable. The excavation face is unstable, small collapses occur locally, large amount of water percolates into the tunnel. Deformation and stresses of ground and supporting system are above average value. In the tunnel entrance, there are visible cracks on the surface of ground.

Construct and monitor the tunnel normally. Increase the monitoring times, inform the construction department.

There is collapse in the tunnel face, sprayed concrete lining break and fall down. The deformation is abnormally great. Possible site failure.

Add monitoring sections and inform all units. Investigate the reasons and prepare temporary counter measures. Take special measures immediately such as intensify temporary supports to ensure safety. Inform all units. Stop construction, deal with the emergency immediately.

3 Case study 3.1

Engineering background

Jing-Wu-Huang/Chang (JWHC) Highway is located in north-east Jiang-Xi province, China. The highway is a main artery connected to An-Hui province and Zhe-Jiang province with 2 lanes in both directions. The total length of the highway is 151.885 kilometers with 17 tunnels of 8.838 kilometers along the highway. While the longest tunnel reaches 1944 meters, the shortest one is only 70 meters in length. Geological conditions in this area are very poor so that monitoring plays an important role in the tunnel construction.

Figure 5. The map of the project

3.2 Application of the monitoring system The IT-based monitoring system was used to manage tunnel monitoring data in JWHC Highway Project. Main functionalities of the system include configuration of multiple tunnels, configuration of monitoring sections, input and query of monitoring data, forecast of monitoring data, and automatic generation of monitoring documents, as illustrated in Figure 6.

1955

Figure 6. Main functionalities of the monitoring system

Figure 7. Start page of the monitoring system

Configuration of multiple tunnels enables users to add new tunnels to system and remove existing tunnels from system. Tunnel information includes tunnel name, background information, length of the tunnel, geological conditions and so on. Configuration of monitoring sections enables site engineers arrange monitoring sections dynamically and assign monitoring items in each section dynamically. Input interfaces are customized for different categories of monitoring items and users can see the latest historical data and a trend curve simultaneously. The system also provides audit capabilities to prevent unintentional mistakes induced in the process of data acquisition and input. Forecast of monitoring data is based on regression analysis and it helps engineers to find the trend of the data and make predictions for constructions. Finally, automatic generation of monitoring documents enables site engineers to focus on the analysis of the data by saving the times which are previously spending on the data collection and curve plotting. Figure 7 illustrates the start page of the monitoring system.

3.3 Discussion on alarming values According to observations of many accidents in mountain tunnel construction project, a schematic and typical form of subsidence of tunnel crown vs. time curve is illustrated in Figure 8. It is shown in the figure that the curve can be divided into 5 stages which are initial stage (curve between point 0 and 1), steady accumulation stage (curve between point 1 and 2), transitional stage (curve between point 2 and 3), acceleration stage (curve between point 3 and 4), and failure stage (curve after point 4).

Figure 8. Five stages of subsidence of tunnel crown vs. time Table 2. Statistical mean values of subsidence of tunnel crown and convergence deformation of tunnel outline Rock grade* II (good) III (fair) Subsidence of tunnel crown divided by the width 0.014 0.092 of tunnel (%) Maximum subsidence rate (mm per day) 0.17 1.04 Convergence deformation value divided by the 0.0054 0.066 length of convergence line (%) Maximum convergence rate (mm per day) 0.09 0.26 *The rock classification is based on Code for Design of Road Tunnel, China.

IV(poor)

V(very poor)

0.34

0.43

5.27

4.35

0.25

0.44

4.65

8.97

Based on the observation data of 17 tunnels of this project, Table 2 gives a statistical mean value of subsidence of tunnel crown and convergence deformation of tunnel outline for double lane mountain tunnel construction.

1956

According to Figure 8 and Table 2, alarming values of subsidence of tunnel crown and convergence deformation of tunnel outline are derived and listed in Table 3. The purpose of alarming values is to provide a basis for the controlling the subsidence of tunnel crown within steady accumulation stage or transitional stage (curve between point 1 and 3, see Figure 8), and to ensure the increasing rate of deformation is under safe control. These alarming values were adopted in the monitoring of tunnel construction in JWHC Highway Project and proven to be reasonable in this project. Table 3. Alarming values of subsidence of tunnel crown and convergence deformation of tunnel outline Rock grade Subsidence of tunnel crown divided by the width of tunnel (%) subsidence rate (mm per day) Convergence deformation value divided by the length of convergence line (%) convergence rate (mm per day)

II (good)

III (fair)

IV(poor)

V(very poor)

0.01~0.05

0.05~0.20

0.10~0.50

0.2~1.0

0.6

2

5

8

0.001~0.01

0.01~0.10

0.10~0.50

0.2~1.2

0.5

2

4

8

4 Conclusions This paper presents the development and implementation of an IT-based mountain tunnel construction monitoring system. The main objective of the system is a centralized database for the monitoring of mountain tunnel construction and dissemination of the information to engineers and contractors through the Internet. Main characteristics of the system include: (1) the capabilities to manage multiple tunnels at the same time, (2) the capabilities to customize monitoring sections and monitoring items; (3) 3D visualization of the monitoring results; and (4) an empirical alarming system to ensure safety of tunnel construction. As demonstrated in this paper, the system can helps to meet demands of improved safety and increased efficiency of the mountain tunnel construction.

5 Acknowledgements This research has been supported by The National High Technology Research and Development Program (863 Program) of China (Grant No. 2006AA11Z102), Shanghai Municipal Science and Technology Commission (Grant No. 052112010). The financial support is gratefully acknowledged.

6 References Ackermann A., Hunt C.B. 2004. The role of digital monitoring technologies in the development of comprehensive tunnel maintenance strategies, Tunnelling and Underground Space Technology, 19(4), 321-321. Chung H.S., Chun B.S., Kim B.H., Lee Y.J. 2006. Measurement and analysis of long-term behavior of Seoul metro tunnels using the Automatic Tunnel Monitoring Systems, Proceedings of the ITA-AITES 2006 World Tunnel Congress and 32nd ITA General Assembly, Seoul, Korea. Kavvadas M. J. 2005. Monitoring ground deformation in tunnelling: Current practice in transportation tunnels. Engineering Geology. 79(1-2), 93-113. Kwon S.W., Kim J.Y., Yoo H.S., Cho M.Y., Kim K.J. 2006. Development of wireless vibration sensor using MEMS for tunnel construction and maintenance. Proceedings of the ITA-AITES 2006 World Tunnel Congress and 32nd ITA General Assembly, Seoul, Korea. Li Y.H., Zhu H.H. 2002. Development of monitoring information system software for geotechnical engineering. Rock and Soil Mechanics, 23(1), 103-106. (in Chinese) Post M.L., van de Linde F.W.J., Rademaker E.J.C. 2004. The Westerschelde Tunnel – using a sensor-based system for durability monitoring of the tunnel lining. Tunnelling and Underground Space Technology, 19(4), 325-325. Wang H., Wu Z.J., Tang H., Wu Y.P., Ge X. R. 2006. Development and application of monitoring information management and prediction software system for underground powerhouse. Rock and Soil Mechanics, 27(1), 163-167. (in Chinese) Ye Y., Wang M.S. 2004. Overview of geotechnical monitoring for tunnel excavation safety, International Symposium on Safety Science and Technology, Shanghai, China, 773-778.

1957