Abstract
Monitoring the deformation of the tunnel can capture the surrounding ground conditions and dynamic changes of the supporting structure at each construction stage of the tunnel,judge the stability of the surrounding rock and the reliability of the supporting structure,and ensure the construction safety and long-term stability of the structure[1].However,the traditional monitoring method is sometimes inefficient,time-consuming,greatly affected by the tunnel environment[2].In order to overcome these limitations of traditional monitoring,this paper adopts a novel wireless monitoring system to monitor the deformation characteristics of surrounding rock and the content of gases(CO)in the process of tunnel construction in real time for a real project of Mopanshan tunnel in south-western of China.Through the analysis of the monitoring data and the actual operation of the construction site,the safety status of the tunnel during the construction process can be assessed in real time,and the variations of tunnel convergence over time can be characterized.At the same time,according to the results of data fusion analysis,the LED risk visualization equipment is used to transform the risk into the color change of the lighting equipment installed on the site,so as to support the construction safety of the tunnel.
As shown in Figure 1,during the tunnel excavation process,four sections were selected for the installation of the laser ranging dip fulcrum.The sensor can measure distance and inclination simultaneously.The sensors arranged in the four sections are used to monitor the convergence value of the tunnel section,and a gas concentration sensing fulcrum and a visual fulcrum are installed at section 2.
Figure 1 Section layout
The installation diagrams of Sections 1,3,and 4 are shown in Figure 2,and the installation diagram of Section 2 is shown in Figure 3.The layout method of section sensor is referred to the related reference[3],[4].Figure 4 shows an installed laser sensor.
Figure 2 Layout of sections 1,3 and 4(unit:mm)
Figure 3 Layout of section 2(unit:mm)
Figure 4 An installed laser sensor
After the sensor is installed,the monitoring data can be obtained from the web-based platform in real time,and the parameters can be set on the computer.During the blasting,due to the splash of the gravel and the large dust near the face of the face,the laser ranging function is limited,so the inclination value is mainly observed during this period.Figure 5 shows the face blasting operation at 8:40,and the CO content in the tunnel hole.It can be seen that a large amount of harmful gas(CO)is generated due to the blasting operation,and the harmful gas content in the tunnel rises sharply to 15.7 mg/m3,which will damage people's health[5].The content of harmful gases rapidly decreased under the action of ventilation equipment after the end of the explosion.
Figure 5 CO content change chart
Figure 6 Dip change chart
Figure 7 Vault to arch waist spacing change diagram
Figure 6 and Figure 7 show the inclination value and vault settlement value of tunnel lining engraved near the tunnel face at the same time.The change value of inclination angle is less than 0.005°and the change of vault and arch waist distance is less than 1 mm,indicating that the structure is relatively stable and not affected by blasting[4],which is consistent with the monitoring results of other sensors.It shows that the monitoring system has good stability and reliability.