Railway tunnel construction safety monitoring system based on AVR32

1.1 Introduction

During the mining, construction and use of railway tunnels, the deformation of tunnel surrounding rock is the most direct and reliable reflection of the surrounding rock stress distribution, overall mechanical morphology change and stable state. The measurement of surrounding rock clearance displacement is an important link in the tunnel construction process and an important basis for judging the stability of surrounding rock and guiding construction. Timely monitoring, analysis and prediction of tunnel surrounding rock deformation has become a very important task in railway tunnel construction to ensure construction safety, prevent accidents and reasonably determine tunnel support.

1.2 Project Background/Motivation for Topic Selection

There are two main methods for measuring displacement of tunnel surrounding rock in traditional ways: one is to arrange the measurement section during the construction process, and measure it manually at regular intervals using various mechanical or mechanical-electronic convergence meters; the other is to measure the section to be measured at fixed points at regular intervals using a tunnel section meter. The shortcomings of both methods are:

(1) Inability to monitor in real time: that is, the deformation of the section to be measured cannot be monitored at any time, and therefore, the abnormal changes in the tunnel surrounding rock during the construction process cannot be reflected in time.

(2) Great interference with construction: Since deformation measurement requires either a ruler or the installation of a cross-section instrument, it has a great impact on construction work, especially transportation operations.

(3) Dangerous measurement work: In places that are difficult for personnel to access, in order to obtain measurement data, personnel have to frequently approach dangerous spaces, which poses a greater threat to the safety of personnel and instruments.

(4) High measurement cost: The same section needs to be measured repeatedly, and the measurement process is complicated, requires many people, and takes a long time, resulting in high measurement costs.

(5) Unreliable measurement data: The main reasons for unreliable measurement data are insufficient measurement accuracy of electronic and mechanical instruments and errors caused when processing measurement data.

We use AVR32 processor to build a new railway construction tunnel safety monitoring system, which has the advantages of non-contact, automation, high precision and high reliability. The system can be used for tunnel construction safety and accident prevention.

2. Demand Analysis

2.1 Functional requirements

The system needs to monitor the safety of railway tunnel construction. As shown in Figure 1, we set up the semiconductor laser on the stable surrounding rock as a reference point. The unstable surrounding rock that needs to be observed is set up with our designed system, which uses the CCD to sense the position of the light spot to reflect the surrounding rock sinking.

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2.2 Performance requirements

The system needs to accurately reflect the situation of the surrounding rock of the railway, and needs to eliminate the influence of external interference factors, such as external temperature and humidity, which will affect the path of light propagation; excessive external light will cause CCD saturation distortion, etc. We need to eliminate these factors to achieve high precision and high reliability.

3. Solution Design

3.1 System Function Implementation Principle

The hardware structure of the system is shown in Figure 2: Based on the AVR EVK1105 evaluation kit, it uses the 32-bit AT32UC3A0512 as the core processor, and has an external expansion of 256M SDRAM and 64M FLASH. The data acquisition part uses Toshiba linear array photoelectric coupling device (CCD) to collect tunnel sinking position information, temperature and humidity sensors to collect tunnel environment information, and light sensors to collect external light intensity information. The display part uses the QVGA (320×240) color LCD display on the board to display the information collected by the data acquisition part. Since the system needs to work for a long time, the collected information needs to be processed accordingly, and it is necessary to display the four interfaces of every minute/hour/day/month, so as to intuitively reflect the short-term and long-term safety of the railway tunnel and evaluate and predict future trends. The control part uses the touch selection button on the board to achieve the effect of displaying different interfaces. The data can be stored through the SD/MMC interface on the board, or transmitted to the monitoring center through the Ethernet interface. When the set threshold is exceeded, a voice prompt can be issued through the high-fidelity audio interface on the board, and the set alarm prompt content can be stored in the FLASH on the board.

The above description is the interface of site 1. Other sites are similar to site 1 and are used to monitor various nodes of the railway tunnel. They can transmit data to the monitoring platform through the Ethernet interface to reflect the overall situation of the entire railway tunnel.

3.2 Hardware platform selection and resource allocation

Hardware platform selection: The 32-bit AVR EVK1105 is an evaluation kit based on the AT32UC3A0512.

On-board resources used: 320×240 QVGA color LCD display, external 256M SDRAM, 64M FLASH, SD/MMC interface, Ethernet interface, light sensor, touch buttons, high-fidelity audio decoding, etc.

3.3 System Software Architecture

As shown in Figure 3, the system first collects three important information: light spot position, temperature and humidity, and external light intensity. According to the corresponding data, the influence of temperature and humidity and external light intensity on the light spot position is eliminated. If the set threshold is exceeded, the high-fidelity voice on the board is used for voice prompts. The processed data is stored in the SD card, displayed on the LCD, and transmitted via Ethernet.

3.4 System Software Process

3.4 Expected Results of the System

Figure 4 shows that we used a notebook to display and process data in the early stage, and the entire system was huge. We used the AVR development kit in advance to complete the drive and design of the corresponding modules, making them miniaturized and practical, and applied them to actual engineering projects.