Application of Real-time Monitoring Technology in Geological Disaster Prevention —— Taking Wushan County Geological Disaster Real-time Monitoring and Early Warning Demonstration Station as an Example

Gao Youlong 1 Zhang Junyi 1 Xue Xingqiao 1 Xie Xiaoyang2

(1 Institute of Hydrogeological Engineering Geology Technology and Method, China Geological Survey, Baoding, Hebei, 071051; 2 Shaanxi Lintong Northwest Research Institute of Chemical Industry, 7 10600)

Based on the practice of geological survey project, the meaning, characteristics and system composition of real-time monitoring of geological disasters are systematically summarized. This paper introduces in detail the construction of the demonstration station for real-time monitoring and early warning of geological disasters in Wushan County, and evaluates the feasibility and reliability of real-time monitoring technology according to the actual operation.

Keywords geological disasters; Real-time monitoring; Remote transmission; Demonstration station

1 Introduction

With the development of modern science and technology and the mutual penetration of marginal disciplines, more and more technologies such as automatic control and network transmission are constantly applied to the monitoring of geological disasters, which greatly improves the automation level of monitoring and relieves the contradiction between insufficient productivity and the sharp increase of geological disasters to some extent. Internationally, the United States, Japan, Italy and other developed countries have established real-time monitoring systems for geological disasters based on parameters such as precipitation, osmotic pressure and slope deformation in a certain area, and realized centralized processing and real-time release of monitoring data with the help of the Internet. In contrast, the real-time and networking level of geological disaster monitoring in China is still low, the function of monitoring information to serve the public has not been clearly reflected, the information channel of early warning is not smooth, and there is a lack of rapid response ability to major geological disasters. Therefore, it is of great practical significance to study the real-time monitoring and early warning of geological disasters in China and implement the real-time monitoring and early warning of major disaster bodies.

In the process of participating in the geological survey project "Research and demonstration of key technologies and methods of geological disaster early warning", the author made a deep research on real-time monitoring technology, and established a demonstration station for real-time monitoring and early warning of geological disasters in Xincheng District, Wushan County, Chongqing, China. After 1.5 years of demonstration operation, the feasibility and reliability of real-time monitoring are verified. Based on the preliminary summary of the demonstration results, this paper is formed with a view to the rapid maturity, popularization and application of real-time monitoring technology and making contributions to the prevention and control of geological disasters in China.

2 The meaning and characteristics of real-time monitoring

Real-time monitoring (RTM) refers to a collection of technologies that enable the personnel in the target layer to know and master the deformation dynamics and development trend of the disaster body at the first time through various monitoring, acquisition, transmission and release technologies, and then make decisions. Its main feature is real-time, that is, the remote target layer personnel can obtain all the deformation information of the disaster body at the first time, and the collection process is automatic without the intervention of the technicians on duty. Obviously, the real-time feature can liberate the labor force to the maximum extent and reduce the risk and operating cost of monitoring personnel.

Compared with the traditional monitoring technology, the data acquisition mode of real-time monitoring is continuous and tracking, and the data acquisition period is very short, usually in a few hours or even shorter. This is of great significance for tracking the deformation process of disaster bodies and carrying out inverse analysis. Its huge data volume usually puts forward higher requirements for supporting software and hardware systems.

It is not difficult to understand that real-time monitoring is also automatic monitoring. The monitoring instruments used need to be automated and unattended. There are two kinds of monitoring instrument automation, one is that the monitoring instrument itself has the function of timing sampling and storage, and the other is that the sampling is controlled by a third-party automatic collector. No matter what method or principle is adopted, its data acquisition can be realized automatically or triggered.

Remote transmission of monitoring data is another main feature of real-time monitoring. Usually, the monitoring center is located in a relatively developed urban area far from the disaster area, and it is necessary to "carry" all kinds of monitoring data with the help of public communication networks or other media, carry out corresponding conversion calculations, and generate the results required by the personnel at the target level. This "processing" process is the remote transmission of monitoring data. Transmission is divided into two ways, one is wired transmission, such as setting up communication cables or optical cables and loading modems at both ends of telephone lines; The other is wireless transmission, such as GSM/GPRS or CDMA network, UHF digital radio station or communication satellite.

Real-time monitoring is a collection of technologies such as automatic data collection, transmission and release. The failure of any link may cause the system to fail to work normally, so real-time monitoring is risky. Its risks include not only the system risks of power supply (such as power failure) and other technical risks such as monitoring instruments (such as sensor and acquisition instrument failures), transmission systems (such as busy lines, insufficient network resources and data security) and publishing systems (such as network congestion, virus invasion and system collapse), but also human resistance risks, such as artificial destruction of monitoring instruments and facilities and malicious attacks on network systems. For risk rescue, in addition to minimizing the safety system risk and technical risk, effective measures such as legislation and publicity are needed to reduce the risk of human resistance, and technicians are set up to maintain the monitoring system immediately to ensure the normal operation of the system.

3 composition of real-time monitoring system

The real-time monitoring system consists of four subsystems: monitoring instruments and facilities, data acquisition system, data transmission system and network publishing system. Each subsystem can run independently or work together in a single chain. Its working principle is shown in figure 1.

Figure 1 Schematic diagram of working principle of real-time monitoring system

3. 1 monitoring instruments and facilities

Monitoring instruments and facilities are the first and most important part to obtain the deformation parameters of the disaster body. They are fixed on the surface or deep part of the disaster body and can characterize the deformation and change of the corresponding parts of the disaster body. The type of monitoring instrument depends on the monitoring method adopted. In the monitoring of geological disasters, the commonly used monitoring methods include surface and deep displacement, stress, groundwater dynamics, ground temperature, precipitation and so on. (table 1). The accuracy, quantity and layout position of monitoring instruments are designed and determined on the basis of geological disaster exploration and comprehensive analysis and the need to control the deformation of disaster bodies. Monitoring instruments usually cooperate with corresponding monitoring facilities, such as monitoring signs (piers) and protective devices, to complete the collection of relevant parameters of disaster bodies.

3.2 Data acquisition system

As the name implies, data acquisition system is used to collect and store all kinds of monitoring data, which is realized by single chip microcomputer or industrial control technology. At present, most monitoring instruments are equipped with data acquisition and storage devices, which can automatically work according to the set data acquisition interval and convert and calculate the original data. Data acquisition equipment usually has RS-232 or other standard communication interfaces, which can easily download data to PC for further analysis and processing. For monitoring instruments without supporting data acquisition equipment or with portable reading equipment, automatic acquisition can be realized through third-party data acquisition equipment. General data acquisition equipment can conveniently convert analog signals such as frequency and voltage into digital signals for storage and processing, and has a standard communication interface for data exchange with PC. Because data acquisition instruments are often placed near monitoring instruments, they are usually connected by cables.

Table 1 Summary of Common Monitoring Techniques and Methods

3.3 Data transmission system

The data transmission system is used to complete the data transmission between the data acquisition instrument, the control center and the user. In fact, the communication between the control center and users is usually realized through the Internet and publishing system, so the narrow sense of data transmission refers to the data transmission between the data acquisition instrument and the control center (that is, from the disaster site to the control center).

According to the spatial distance between the disaster body and the control center, data transmission can be divided into two types: short-distance data transmission (generally less than 2km) and long-distance data transmission. Because of the short transmission distance, the former usually adopts cable connection, while the latter adopts remote data transmission device.

According to the transmission medium, remote data transmission can be divided into wired transmission and wireless transmission. At present, the commonly used wired transmission methods include telephone line connection (that is, loading Modem data at both ends of the telephone line) and optical cable connection. Wireless transmission modes include digital radio station (medium and long distance), GSM/GPRS or CDMA mobile communication network, communication satellite, etc. (Figure 2).

Fig. 2 Common data transmission methods

3.4 Information Release System

The information publishing system provides all kinds of monitoring information to the target layer personnel (that is, users) in the form of Web home page through the Internet. Monitoring information includes geological conditions, development characteristics, monitoring network layout, multiple monitoring data, curve changes of monitoring data with time, monitoring information announcements, pictures and videos, etc.

The information publishing system consists of two parts: the underlying database and the publishing homepage. The former is used to manage all kinds of basic information and monitoring data, providing data source for the latter, and the latter provides information access platform for users. Usually, the data exchange between them adopts B/S architecture.

Once the information release system is established, some descriptive words such as geological conditions, development characteristics and monitoring network layout will be relatively fixed and will not change greatly in a short time. This information is usually called static information. With the passage of time, information such as monitoring data and its curves are constantly generated and show dynamic changes, which need to be automatically updated and displayed on the home page. This information is called dynamic information. To realize the real-time release of monitoring data, it is necessary to establish a dynamic home page to display dynamic data.

Because the monitoring data is managed by the underlying database, as long as the monitoring data is automatically written into the database immediately and the data source is updated at any time on the dynamic homepage, it can be automatically displayed, that is, published in real time. it is quite easy to do so.

Brief introduction of real-time monitoring demonstration station of geological disasters in Wushan county

The new urban area of Wushan County in Chongqing is one of the most serious geological disasters in China, and about13 of the county's available construction land is threatened by geological disasters to varying degrees. Through demonstration and comparison, among 27 large-scale landslides (collapses) in urban areas, Xiangjiagou landslide and Yuhuangge landslide, which have obvious deformation and serious damage recently, are selected to establish a real-time monitoring and early warning system for application demonstration. The surface displacement is monitored by GPS, the deep displacement is monitored by fixed borehole inclinometer and TDR technology, and the pore water pressure, saturated water level and water temperature of sliding body are monitored by pore water pressure monitor. At the same time, the monitoring of ground temperature, precipitation and reservoir water level should be considered by installing additional functions of instruments or collecting them regularly. Up to now, * * * has established 22 GPS monitoring marks (including datum points), 3 fixed borehole inclinometers, 3 TDR monitoring points (holes) and 7 measuring points for pore water pressure monitoring. A variety of monitoring instruments are installed in the same geographical position in the same group, which not only facilitates the mutual verification and comparison of data between different monitoring methods, but also can collect and transmit a variety of monitoring data by using only one collecting instrument and transmission device, thus reducing the construction cost of the monitoring system; In addition, the installation in the same group is convenient for the construction of monitoring machine room (station) and protects monitoring instruments and facilities. The above-mentioned monitoring methods adopt real-time monitoring except that GPS adopts regular observation due to engineering cost, human resistance risk and other reasons.

4. 1 demonstration station data acquisition system

Fixed borehole inclinometer, TDR and pore water pressure monitor all have supporting data acquisition devices. Among them, TDR monitoring technology uses industrial control computer as data acquisition equipment, which can just be used as the upper computer of the other two monitoring instruments. Through multi-serial port expansion, the fixed borehole inclinometer and pore water pressure monitor are connected to the industrial computer, and the stored data are downloaded regularly and transmitted to the control center at a predetermined time. At the same time, data backup is stored in the industrial computer to prevent data loss. The structural diagram of the data acquisition system of the demonstration station is shown in Figure 3.

Fig. 3 Structure diagram of data acquisition system of demonstration station

4.2 GPRS remote wireless transmission system

The control center of the demonstration station is located in Wushan County Land and Resources Bureau, with a linear distance of 2.74km from Xiangjiagou landslide and about 0.6km from Yuhuangge landslide, during which GPRS network is used for long-distance wireless data transmission.

GPRS (General Packet Radio Service) is a 2.5G data carrying service developed by China Mobile Communication on GSM network, which has the advantages of fast transmission speed, always on-line and charging by volume. GPRS uses TCP/IP protocol, which is convenient to write data to the designated server (with a fixed IP address).

The hardware of GPRS data transmission is a commercial GPRS-MODEM, and the control software is written by ourselves to control the data transmission time, destination address and error handling during transmission. It consists of two parts: server and client. The server is used to set the network configuration, database connection mode and storage paths of data files, log files and configuration files. The client is installed on the data acquisition instrument (industrial computer) of the field station, and controls network connection, upload time, data coding, data backup and transmission error handling. The client software and all data acquisition software are set to work continuously. When working according to the control parameters, they receive configuration instructions from the control center to adjust the control parameters immediately.

4.3 Demonstration Station Information Release System

The hardware of the demonstration station information publishing system consists of 1 small server and 100M LAN 2 PC terminals. Use 2M bandwidth to surf the Internet through ADSL. The underlying database and WEB homepage are installed on the server at the same time. The server operating system is Microsoft Windows Server 2000, and the database system is Microsoft SQL Server 2000. The homepage of the website is written in ASP.NET and C+visual language, and it is in B/S structure with the database. In virus protection and network security, commercial software Rising RAV 2004 and Skynet firewall system are adopted.

(1) database system

The database system is the foundation of the information publishing system, which is divided into three parts according to the management content: basic information management, data management and auxiliary information management. The contents of basic information management include monitoring stations (including central stations and field stations), monitoring boreholes, monitoring points, releasing information, releasing pictures, etc. Data management includes fixed borehole inclinometer, GPS, TDR monitoring system, BOTDR monitoring system, pore water pressure monitor, environmental temperature, precipitation, reservoir water level, etc. Auxiliary information management includes user classification, information download, access statistics and so on. The database system structure is shown in Figure 4.

(2) Data servo processing program

The data servo processing program is used to convert and calculate the data from the field station, and immediately write the processing results into the database. The processing program is written in Visual BASIC language, and the database writing process is triggered by the timing function controlled by timer. After the database writing process is completed, the original data is deleted to prevent rewriting. It is not difficult to see that the data servo program is the connector of the transmission system and the distribution system, which organically combines the two independent systems.

(3) Demonstration Station Information Release Homepage

The information release homepage provides remote users with all the information they need, including the overview of demonstration stations, real-time monitoring curves, latest monitoring data, etc. From the perspective of publishing information content, access mode and management and maintenance, the homepage is designed as navigation area, publishing area, management area and download area to provide interaction for remote users and administrators.

Fig. 4 Block diagram of database system of demonstration station

The navigation area provides necessary navigation information for remote users, including announcement information, pictures and links to related professional websites, and shows the progress of demonstration station construction, phased achievements and related early warning contents.

The release area is used to provide the overview, real-time monitoring curve and data query of the demonstration station.

The general situation of the demonstration station includes natural geographical conditions, geological conditions, overall deployment of the demonstration station, and performance indicators of monitoring instruments and facilities (GPS, fixed borehole inclinometer, TDR, BOTDR, pore water pressure monitor, etc.). ), as well as the basic information of monitoring stations (including central stations), monitoring boreholes and monitoring points.

Real-time monitoring is used to display various monitoring curves and is the core content of publishing the home page. From the point of view of convenient access, the real-time monitoring adopts the display mode of "selecting disaster body-selecting monitoring profile-selecting monitoring point-selecting monitoring period-displaying monitoring curve", which is opened step by step and peeled off layer by layer, all of which are linked in a graphical way, thus enhancing the intuition of access. The coordinates of the monitoring curve are designed to be adaptive, the size of the graph is set in the configuration file of the system, and the latest update time of the data is indicated. Curves are displayed in the form of pictures, and users can easily download them to their own PC for storage.

For security reasons, data query is encrypted, and users can only view it after logging in with authorized user name and password. The query adopts the combined filtering method of "select monitoring method-select monitoring point-select monitoring start time-display data table". After the defined parameters are entered and submitted, the system searches all the qualified records from the underlying database, and displays them in the form of a list after sorting by date. Users can select all or part of the query results, paste them on personal computers, and save them as WORD documents.

The administrative area is specially designed for system administrators. It is used for administrators to remotely manage information such as words, pictures and data, and to add, modify, delete, upload and download information. It is divided into four independent modules: information management, picture management, data management and download management, with advanced functions such as fuzzy search.

The download area provides authorized users with the download function of working pictures, videos, monitoring reports, software and other large files, which supplements the shortcomings of the home page in file exchange.

The layout of the home page is shown in Figure 5. For more information about the publishing system, please visit Http://www.wss.org.cn.

Operation evaluation of real-time monitoring system of demonstration station 5

Because this paper focuses on the feasibility and reliability of real-time monitoring technology, there is no more analysis of monitoring results and landslide stability dynamics. It is obvious from the above discussion that it is technically feasible to build a real-time monitoring system in geological disaster monitoring. This section simply evaluates the reliability of the collection system, transmission system and power distribution system of Wushan County real-time monitoring and early warning demonstration station from two aspects: fault statistics and fault cause analysis, and puts forward some targeted improvement suggestions.

Figure 5 Demonstration Station Information Publishing Home Page

According to the work log of the construction of the geological disaster monitoring and early warning demonstration station in Wushan county, the failure of the monitoring system mainly occurs in the transmission subsystem, and the failure form is that the data is not transmitted or the transmission is incorrect, mainly because the GPRS network signal is unstable and the transmission is randomly interrupted; Secondly, repeated attempts to connect after a failed dial-up connection lead to long-term ineffectiveness, which repeatedly occupies port 80 of the server and cannot access the network correctly when the maximum number of connections of the server is exceeded; Thirdly, the irregular power failure in the monitoring area will often make the security system fail, thus losing data. In addition, the server system of the demonstration station suffered virus damage and malicious attacks, which led to two crashes of the network system. It can be seen that the real-time monitoring system can run stably and reliably under the condition of complete basic communication conditions and guarantee system. By installing a long-term standby power supply system, a fully functional virus firewall and a network firewall in the construction process, the risk of the security system can be effectively reduced and the stability of the system operation can be further improved.

6 conclusion

The demonstration stations for real-time monitoring and early warning of geological disasters in Wushan County have been built and put into operation since 2003. Under the maintenance of technicians, the system runs normally, obtaining hundreds of thousands of monitoring data, publishing nearly 100 announcement information and pictures, and compiling several issues of monitoring analysis briefing, realizing remote real-time acquisition of monitoring information and achieving good demonstration effect. Practice has proved that it is completely feasible and reliable to apply real-time monitoring technology to the prevention and control of geological disasters. It can be predicted that real-time monitoring technology will be the inevitable development trend of geological disaster monitoring.

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