Field Measurements and Numerical Simulations of Temperature and Moisture in Highway Engineering Using a Frequency Domain Reflectometry Sensor
Abstract
:1. Introduction
2. Field Measurement Based on Agricultural-Purpose FDR Sensor
2.1. Basic Composition and Testing Principle of FDR Sensor
2.1.1. Basic Composition
2.1.2. Testing Principle
2.2. Embedding of an Agricultural-Purpose FDR Sensor
2.2.1. Project Overview
2.2.2. Embedding Method and Process
- (1)
- Embedding FDR sensor in old subgrade: drill horizontally to the predetermined depth at the side slope of the old subgrade with a drilling machine (borehole diameter: 11.0 cm); install the FDR sensor on one end of the PVC tube (diameter: about 5 cm), and push it to the bottom of the borehole from the other end of the PVC tube to make it completely and closely inserted into soil horizontally (in the old subgrade).
- (2)
- Embedding FDR probes in new subgrade: at the preset subgrade elevation, compact and level the subgrade surface and excavate a pit (L × W × D: 40 cm × 30 cm × 20 cm) manually at a certain interval; then closely insert the probe into soil along the bottom of the pit in a lateral direction (the inserting direction is vertical to the longitudinal direction of the subgrade); last, excavate a small groove along the cross section of the newly-filled subgrade (W: 10 cm; D: 20 cm; L: 750 cm (viz. the width of the entire newly-filled subgrade)) to embed the sensor wire into the groove and lead it to the outer side of the subgrade slope. The embedding flow diagram and field embedding sketch for FDR sensors are shown in Figure 2 and Figure 3, respectively.
2.3. Data Acquisition and Transmission
3. Numerical Simulation Based on Measured Data
3.1. Theoretical Model and Boundary Conditions
3.1.1. Numerical Model
3.1.2. Calculation Equation for Flow Boundary Condition
3.1.3. Temperature Boundary Conditions
3.2. Geometric Model for Finite Element Calculation
3.2.1. Measured Climatic Parameters
3.2.2. Other Parameters
3.3. Calibration for the Finite Elements
4. Measured Results and Analyses
4.1. Temperature Observations
4.2. Moisture Content Observations
4.3. Comparative Analysis of Field Measurements and Numerical Simulations
4.3.1. Comparative Analysis of Temperature
4.3.2. Comparative Analysis of Moisture Content
5. Conclusions
- (1)
- FDR sensors were applied to the subgrade in a highway reconstruction project for the first time, and the embedding method and process of the sensors are illustrated. During a monitoring period of over two years, all embedded sensors present reasonable performance for monitoring the temperature and moisture inside the subgrade soil. This implies that the embedding method and process proposed in this paper are reasonable and also indicates that agricultural-purpose FDR sensors are applicable to the subgrade in highway reconstruction and extension projects.
- (2)
- By means of the small weather station built in the field and the GPRS module performing wireless transmission, the real-time data monitored by FDR sensors can be acquired remotely. Thus, the labor cost can be largely reduced and analysis of real-time data monitored is accessible, thereby enhancing timely and effective evaluation of subgrade performance.
- (3)
- Comparison between the measured results by FDR sensors and computed results from numerical simulation also demonstrated that the FDR sensor can effectively reflect the temperature and moisture changes inside subgrades, especially at the junction between the old and new subgrades, the measured values are more reasonable and effective than the calculated values, and can reflect the temperature and moisture changes caused by the climatic environment more accurately.
- (4)
- The paper provides a new method and idea for highway researchers to monitor long-term changes of the temperature and moisture inside the subgrade, and further inspect its long-time performance. This method can be also extended to railway embankments, prevention and treatment of slopes foundation engineering and other civil engineering projects which are affected by soil moisture content and temperature.
Acknowledgments
Author Contributions
Conflicts of Interest
Appendix A
Project | Indicators | Note |
---|---|---|
Measurement parameters | Measured medium volumes of moisture content | - |
Application objects | Soils, other solids or powdered medium | - |
Accuracy of measurement | ±0.5% vol ((if the soil was calibrated) ±2.0% vol (direct measurement) | Range of 0~saturated water content |
Resolution ratio | ±0.1% vol | - |
Deviation caused by Salinity | Not more than 3.5% vol (0 saturated moisture content) | FDR can be used after calibrating |
Power consumption | 22 mA (characteristic value) | - |
Supply voltage | 9–12 V | - |
Output signal | 0–1200 mV | - |
Measurement of volume | 60 mm (length) × 30 mm (diameter) | - |
Work environment | −30 °C~+50 °C | - |
Appendix B
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Name | Function Relationship | Range of Application |
---|---|---|
Relationship between Soil volumetric water content and voltage | θ = 144.7 υ4 − 285.0 υ3 + 195.0 υ2 − 5.277 υ | Υ ≤ 1.005 V |
θ = 500.0 υ − 452.5 | 1.005 V < υ ≤ 1.085 V | |
θ (% vol) = 100 | 1.085 V < υ | |
Relationship between soil temperature and voltage | T = 10.312 × (υ/100) − 81.25 | −30 °C~+50 °C |
Parameter Category | Relevant Parameter | Symbol | Unit |
---|---|---|---|
Meteorological parameters | Daily average temperature | T | °C |
Daily relative moisture | RH | % | |
Daily relative wind speed | u | m/s | |
Daily average rainfall | Pr | mm | |
Hydraulic properties of soil | Saturated infiltration coefficient | kws | m/s |
Soil-Water Characteristic Curve | SDSWCC | - | |
Thermodynamic properties of soil | Heat conductivity coefficient | λt | - |
Specific heat per unit volume | λv | J/(m3·°C) | |
Physiological parameters of vegetation | Leaf area index | LAI | - |
Root depth index | DR | m |
Material | a | n | m | Sr | θs | R2 |
---|---|---|---|---|---|---|
Low Liquid-Limit Clay | 129.331 | 1.476 | 0.555 | 106 | 40.32% | 0.973 |
Materials | Initial Degree of Saturation (%) | Infiltration Coefficients (m/s) | Soil Water Characteristic Curve Parameters | Thermal Conductivity Coefficient | Volumetric Heat Capacity (J·m−3) | ||
---|---|---|---|---|---|---|---|
a | n | m | |||||
Foundation | Value of groundwater | 4.75 × 10−6 | 72.01 | 1.62 | 0.48 | 2.742 | 2.76 × 106 |
low liquid-limit clay | 75 | 1.15 × 10−8 | 129.33 | 1.48 | 0.56 | 2.354 | 2.85 × 106 |
Asphalt pavement | - | 1.0 × 10−14 | - | 1.010 | 1.98 × 106 |
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Yao, Y.-S.; Zheng, J.-L.; Chen, Z.-S.; Zhang, J.-H.; Li, Y. Field Measurements and Numerical Simulations of Temperature and Moisture in Highway Engineering Using a Frequency Domain Reflectometry Sensor. Sensors 2016, 16, 857. https://doi.org/10.3390/s16060857
Yao Y-S, Zheng J-L, Chen Z-S, Zhang J-H, Li Y. Field Measurements and Numerical Simulations of Temperature and Moisture in Highway Engineering Using a Frequency Domain Reflectometry Sensor. Sensors. 2016; 16(6):857. https://doi.org/10.3390/s16060857
Chicago/Turabian StyleYao, Yong-Sheng, Jian-Long Zheng, Zeng-Shun Chen, Jun-Hui Zhang, and Yong Li. 2016. "Field Measurements and Numerical Simulations of Temperature and Moisture in Highway Engineering Using a Frequency Domain Reflectometry Sensor" Sensors 16, no. 6: 857. https://doi.org/10.3390/s16060857
APA StyleYao, Y.-S., Zheng, J.-L., Chen, Z.-S., Zhang, J.-H., & Li, Y. (2016). Field Measurements and Numerical Simulations of Temperature and Moisture in Highway Engineering Using a Frequency Domain Reflectometry Sensor. Sensors, 16(6), 857. https://doi.org/10.3390/s16060857