# Alternate Method of Pavement Assessment Using Geophones and Accelerometers for Measuring the Pavement Response

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## Abstract

**:**

## 1. Introduction

#### Objectives

## 2. Geophones and Accelerometers Selected for Pavement Deflection Measurement

#### Selecting the Sensors to Measure Pavement Deflection

- The typical deflection levels are between 0.1 and 1 mm, hence sensors should be sensitive enough to carry measurements in this range.
- The resonance frequency of the sensors should be low when compared to the frequency of the deflection signals (typically between 2 and 20 Hz).
- The sensors should have a small size, to facilitate embedment in the pavement layers
- Durability, mechanical resistance, and stability of the sensor response are also important factors, as pavement measurements need to be performed over periods of several years.
- Relatively limited cost, to enable widespread use of this type of instrumentation.

## 3. Pavement Modelling with Alize

#### Displacement Signals

## 4. Laboratory Tests

- The sensitivities of the geophones and accelerometers.
- Signal responses for different amplitudes and velocities.
- The intrinsic parameters like low-frequency noise that affect the response of the devices.

- (1)
- The direct integration process tends to attenuate the low-frequency components of the signal [8]. The integration process also introduces a constant, and thus adds a continuous component to the signal. This may explain the unrealistic shape of the signal, with positive displacement values.
- (2)
- In addition, as can be seen, the raw geophone and acceleration signals present some noise, which can also lead to inaccurate results. The noise generates high-frequency variations in the response signals, which do not represent the actual vertical displacement of the pavement and needs to be filtered [14].

## 5. Signal Processing and Filtering of Sensor Responses

#### 5.1. Scheme to Convert the Sensor Response into Vertical Displacement and Improving the Accuracy

_{a}(t) corresponds to the envelope of the signal s(t),. This analytical signal is determined by the amplitude (A) and phase Ø, defined by

#### 5.2. Comparison of the Reference Laser Sensor with the Improved Measurements

#### 5.3. Results

## 6. Accelerated Pavement Tests

#### 6.1. Experimental Setup

- Thicknesses of the different layers were determined from the controls made during and after construction
- Bituminous material complex moduli were determined from laboratory tests on the field produced mix
- The moduli of the granular layer were determined by back-calculation, from FWD measurements
- The moduli of the subgrade were determined from Benkelman beam deflection measurements.

#### 6.2. Tests Results

- The error values are relatively low for all the sensors and test conditions (the highest error is 13.7%).
- The errors are slightly higher for the 45 kN load level than for the 55 and 65 kN load levels. A possible explanation is that the tests at 45 kN were performed right at the start of the APT test, and that some post compaction, and movement of the transducers may have occurred during these first load cycles and affected the accuracy of the measurements.
- For the 55 and 65 kN load levels, mean error values for all the transducers are similar, and very satisfactory (between 3.55% and 5.03%). This validates the original signal treatment procedure used for the calculation of deflections.

## 7. Data Analysis

#### 7.1. Back Calculation Methodology

- The initial characteristics of the pavement (layer thicknesses, initial layer moduli) are entered in Alize
- The characteristics of the wheel load are entered in Alize.
- The measured deflection basin is discretized into a certain number of points to be inputted in the software
- lower and upper limits are defined for the moduli of each layer, for the optimization process (the values used are given in Table 4).
- Successive pavement response calculations are carried out until the best match between the calculated and measured deflections, and thus the best estimate of the pavement layer moduli is obtained.

#### 7.2. Estimation of Pavement Layer Moduli

## 8. Conclusions

## Author Contributions

## Funding

## Conflicts of Interest

## References

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**Figure 2.**Deflection signal obtained with the ALIZE pavement-modelling software, corresponding to a 5-axle truck load.

**Figure 9.**Example of comparison between the geophone signal obtained with and without the improved processing method.

**Figure 10.**(

**a**): Displacement measurements with geophones at a speed of 70 km/h and amplitude of 0.8 mm. (

**b**): Displacement measurements with accelerometers at a speed of 70 km/h and amplitude of 0.8 mm.

**Figure 16.**(

**a**): Deflection for 45 kN and speed of 8 m/s. (

**b**): Deflection for 45 kN and speed of 20 m/s. (

**c**): Deflection for 55 kN and speed of 8 m/s. (

**d**): Deflection for 55 kN and speed of 20 m/s. (

**e**): Deflection for 65 kN and speed of 8 m/s. (

**f**): Deflection for 65 kN and speed of 20 m/s

**Figure 17.**(

**a**): Deflections at position 6 and 45 kN load. (

**b**): Deflections at position 4 and 45 kN load. (

**c**): Deflections at position 6 and 55 kN load. (

**d**): Deflections at position 4 and 55 kN load. (

**e**): Deflections at position 6 and 65 kN load. (

**f**): Deflections at position 4 and 65 kN load.

**Figure 18.**(

**a**): Variation of deflections with the loading speed (from 6 to 20 m/s) for load levels 45 kN. (

**b**): Variation of deflections with the loading speed (from 6 to 20 m/s) for load levels 55 kN. (

**c**): Variation of deflections with the loading speed (from 6 to 20 m/s) for load levels 65 kN.

**Figure 19.**(

**a**): Evolution of deflections with the position of the wheels, for 45 kN load and 16 m/s speed. (

**b**): Evolution of deflections with the position of the wheels, for 55 kN load and 16 m/s speed. (

**c**): Evolution of deflections with the position of the wheels, for 65 kN load and 16 m/s speed.

**Figure 21.**(

**a**): Deflection fitting for Accelerometer CX Figure 21(

**b**): Deflection fitting for Accelerometer SD. (

**c**): Deflection fitting for Geophones ION. (

**d**): Deflection fitting for Geophones GS11D. (

**e**): Deflection fitting for anchored deflectometer.

Materials | Elastic Modulus (MPa) | Thickness (cm) |
---|---|---|

Bituminous mixture | 7000 | 11 |

Unbound granular material | 200 | 30 |

Subgrade | 80 | 250 |

Pavement Layer | Thickness (cm) | Modulus (MPa) |
---|---|---|

Bituminous concrete | 11 | 9441(15 °C and 10 Hz) |

Granular base | 30 | 145 |

Subgrade | 260 | 110 |

**Table 3.**relative differences in percentage between the reference deflections (anchored displacement sensors) and those measured by the geophones and accelerometers, for 45, 55, and 65 kN loads.

LOAD 45 KN and SPEED (m/s) | ACC-SD | ACC-CX | Geophone-Ion | Geophone-GS11D |

6 | 7.78% | 12.27% | 9.36% | 7.28% |

8 | 7.95% | 7.70% | 5.44% | 11.54% |

12 | 13.74% | 9.90% | 6.87% | 11.13% |

16 | 6.30% | 5.86% | 5.93% | 4.70% |

20 | 6.07% | 6.21% | 5.50% | 5.52% |

Mean | 8.37% | 8.39% | 6.62% | 8.03% |

LOAD 55 kN and SPEED(m/s) | ACC-SD | ACC-CX | Geophone-Ion | Geophone-GS11D |

6 | 4.52% | 9.39% | 4.49% | 4.59% |

8 | 2.76% | 2.51% | 2.89% | 4.71% |

12 | 4.33% | 4.54% | 3.63% | 3.39% |

16 | 4.19% | 4.31% | 3.75% | 4.39% |

20 | 3.71% | 4.40% | 3.28% | 3.60% |

Mean | 3.90% | 5.03% | 3.61% | 4.14% |

LOAD 65 kN and SPEED(m/s) | ACC-SD | ACC-CX | Geophone-Ion | Geophone-GS11D |

6 | 2.65% | 6.25% | 2.66% | 3.84% |

8 | 3.24% | 3.64% | 2.25% | 2.84% |

12 | 4.86% | 4.27% | 4.69% | 2.70% |

16 | 4.84% | 5.15% | 4.63% | 4.11% |

20 | 4.09% | 4.52% | 3.54% | 4.73% |

mean | 3.94% | 4.77% | 3.55% | 3.64% |

Pavement Layer | Lower Modulus Limit (MPa) | Upper Modulus Limit (MPa) |
---|---|---|

E1 | 8000 | 12000 |

E2 | 100 | 200 |

E3 | 50 | 150 |

**Table 5.**Back-calculated pavement layer moduli obtained with ALIZE for the different sensors, and comparison with reference values.

Pavement Layer | Reference Moduli (MPa) | Anchored Deflectometer (MPa) | ACC-SD (MPa) | ACC-CX (MPa) | Geophone-Ion (MPa) | Geophone-GS11D (MPa) |
---|---|---|---|---|---|---|

Asphalt layer | 9442 | 8877 | 10,348 | 10,788 | 9189 | 8010 |

UBG | 145 | 157.4 | 118.1 | 104.2 | 109.0 | 150 |

Soil | 110 | 124.2 | 117.1 | 124.4 | 138.3 | 126.7 |

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**MDPI and ACS Style**

Bahrani, N.; Blanc, J.; Hornych, P.; Menant, F.
Alternate Method of Pavement Assessment Using Geophones and Accelerometers for Measuring the Pavement Response. *Infrastructures* **2020**, *5*, 25.
https://doi.org/10.3390/infrastructures5030025

**AMA Style**

Bahrani N, Blanc J, Hornych P, Menant F.
Alternate Method of Pavement Assessment Using Geophones and Accelerometers for Measuring the Pavement Response. *Infrastructures*. 2020; 5(3):25.
https://doi.org/10.3390/infrastructures5030025

**Chicago/Turabian Style**

Bahrani, Natasha, Juliette Blanc, Pierre Hornych, and Fabien Menant.
2020. "Alternate Method of Pavement Assessment Using Geophones and Accelerometers for Measuring the Pavement Response" *Infrastructures* 5, no. 3: 25.
https://doi.org/10.3390/infrastructures5030025