Comparison and Analysis of Measured Data from Flexible Inclination Meters and Manual Inclination Meters on the High Slope of the Longchuan-Huaiji Expressway (Large Deformation)
1. Project Overview
The Longchuan-Huaiji Expressway (Longchuan to Lianping section) in Guangdong Province features a right-side high slope project with a total of 10 levels, each with platform widths ranging from 3 to 103 meters. The first and second levels of the slope are 10 meters high, with slope ratios of 1:1.00 and 1:1.75, respectively. The third to sixth levels and the ninth to tenth levels are 8 meters high, while the seventh and eighth levels are 7.5 meters high. The second, third, fifth to tenth levels have slope ratios of 1:2.00, and the fourth level has a slope ratio of 1:3.00. The second and third levels feature wide platforms, with the widest being 103 meters; the sixth level has a wide platform with a maximum width of 40 meters. The first and second level slopes use steel flower tube grouting frame protection, while the second level slope employs a truss framework, and the ninth and tenth levels are protected with shotcrete. The other slopes use grass sowing for protection. A row of anti-slide piles with a diameter of φ260 cm and lengths between 27 and 45 meters is set up on the first and second level platforms.
During construction, there was a previous landslide, which was managed through unloading, support, and drainage measures. Long-term monitoring is conducted to observe the deformation of the slope and ensure road safety.
2. Layout and Installation of Monitoring Points
To comprehensively assess the slope's stability and facilitate the analysis of landslide instability types, flexible inclination meters are installed in the upper, middle, and lower parts of the slope to monitor sliding deformation in the upper slope, the relationship between the upper and lower slopes, and the deformation of the lower slope affecting traffic. The layout of the monitoring points and overhead photos of the site are shown in Figures 2-1 and 2-2.
Figure 2-1: Monitoring Point Layout Map
Figure 2-2: Overhead Photo of the Site
Three monitoring points for deep horizontal displacement of flexible inclination meters and manual inclination tubes are installed at the same location on the slope, with the same depth. Installation and debugging were completed in mid-April 2021, with initial values tested on April 20.
Figure 2-3: Installation Process Photos of Flexible Inclination Meters
Figure 2-4: Completed Installation of Flexible Inclination Meter
3. Monitoring Results Comparison
3.1 Comparison Conditions Setup
To verify the reliability of measurements under all scene conditions with the flexible inclination meter, the internationally recognized Digitilt DataMate II manual monitoring device was used for comparison. Different working conditions and continuous heavy rainfall effects were taken into account, as shown in Table 3-1.
Table 3-1: Comparison of Monitoring Methods
Table 3-2: Correspondence between Manual and Automated Monitoring Points
3.2 Data Comparison Analysis
The manual monitoring hole CX-6 (destroyed by shear after July 2021) and the flexible inclination meter monitoring hole ZDCX-1 are both located at the same position on the ninth level platform, with monitoring data collected from April 25, 2021, to June 28, 2021, with April 25, 2021, as the initial value.
Figure 3-5: Time Series Curve of Deformation for Manual Monitoring Hole CX-6 at 19m Depth
Figure 3-6: A and B Direction Deformation Curve for Manual Monitoring Hole CX-6
Figure 3-7: Automated Deformation Trend of ZDCX-1
Figure 3-8: Shear Surface Profile for Automated Monitoring Hole ZDCX-1 at 19m Depth
Figures 3-5 and 3-6 represent the time process and spatial distribution curves for manual monitoring data, while Figures 3-7 and 3-8 show the spatial distribution and time process curves for automated monitoring data. The analysis indicates that the curves for manual and automated monitoring data are consistent in direction and shape during the monitoring period, with sliding shear positions measured between 19m to 20m. At a depth of 19m, the manual monitoring data shows A direction 49.6 mm and B direction -20.1 mm, while the automated monitoring data shows A direction 64.3 mm and B direction -30.5 mm, indicating a general agreement in deformation vector directions. The manual monitoring, due to its low frequency, failed to detect a sudden change on June 11; however, automated monitoring can continuously and in real-time observe the complete process of slope deformation and its variations.
After July 2021, the manual monitoring hole CX-6 was unable to continue collecting inclination data due to excessive deformation, while the automated monitoring hole continued effective monitoring. By August 2022, the maximum cumulative displacement for this monitoring hole was 1,978.7 mm, with the flexible inclination meter successfully capturing this deformation process.
Figure 3-9: Cumulative Displacement Distribution Map for Automated Monitoring Hole ZDCX3-1
4.Conclusion
Through the comparison and analysis of multiple locations and all-weather data from the Longchuan-Huaiji Expressway (Longchuan to Lianping section) high slope project with internationally recognized products and precise manual measurements, the following conclusions can be drawn:
（1）Compared to the data collected by the high-precision manual monitoring instrument Digitilt DataMate II, the Huasu Measurement Control flexible inclination meter monitoring system demonstrates high accuracy.
（2）The flexible inclination meter automated monitoring system can continuously and in real-time observe, providing better temporal and spatial resolution and precision, effectively detecting sudden changes like those on June 11, surpassing manual monitoring in accuracy and effectiveness.
（3）By July 2022, the manual monitoring holes CX-6 and CX-5 were destroyed by slope shear, while the flexible inclination meter automated monitoring system continued to operate effectively, demonstrating strong adaptability to large deformations and suitability for harsh conditions or emergency scenarios.
（4）The flexible inclination meter at ZDCX-3 was relocated from other slope areas to continue monitoring at the CX-16 hole in the middle of the third level slope, achieving good monitoring results, indicating that this flexible inclination meter has the advantages of reusability, mobility, and ease of installation and debugging.