The rolling wheel deflectometer (RWD) offers the benefit to measure pavement deflection without causing any traffic interruption or compromising safety along tested road segments. This study describes a detailed field evaluation of the RWD system in Louisiana in which 16 different test sites representing a wide array of pavement conditions were tested. Measurements were used to assess the repeatability of RWD measurements, the effect of truck speeds, and to study the relationship between RWD and falling weight deflectometer (FWD) deflection measurements and pavement conditions. Based on the results of the experimental program, it was determined that the repeatability of RWD measurements was acceptable with an average coefficient of variation at all test speeds of 15 percent. In addition, the influence of the testing speed on the measured deflections was minimal. The scattering and uniformity of the FWD and RWD data appears to closely follow the conditions of the roadway. Both test methods appear to properly reflect pavement conditions and structural integrity of the road network by measuring a greater average deflection and scattering for sites in poor conditions. RWD deflection measurements were in general agreement with FWD deflections measurements; however, the mean center deflections from RWD and FWD were statistically different for 15 of the 16 sites. This study developed and validated a direct and simple model for determining the pavement structural number (SN) using RWD deflection data. To develop this model, the relationship between the average RWD surface deflection and the peak FWD deflection was investigated. The developed model correlates a pavement’s SN to two RWD-measured properties (average RWD deflection and RWD index). The developed model was fitted to RWD data collected in 16 road sections (each 1.5 miles), referred to as research sites, in Louisiana. The model was then validated based on FWD and RWD data collected on 52 road sections in Louisiana. Results showed a good agreement between SN calculations obtained from FWD and RWD deflection testing. While the developed model is independent of the pavement thickness and layer properties, it provides promising results as an indicator of structural integrity of the pavement structure at the network level. The fitting statistics support the use of the proposed model as a screening tool for identifying structurally deficient pavements at the network level. Based on the RWD evaluation conducted in District 05, this study recommends extending the use of RWD to the other districts in Louisiana.

https://www.ltrc.lsu.edu/pdf/2012/fr_492.pdf

Implementation of Rolling Wheel Deflectometer (RWD) in PMS and Pavement Preservation

Surface distress is a fairly good indicator of rehabilitation needs but it does not directly relate to remaining life estimates. Mechanistic pavement design requires that strains be calculated utilizing more or less complex modeling. Over the years many devices measuring surface deflections under a given load have been developed. The device by choice for assessing strains due to load is the falling weight deflectometer (FWD). It creates an impulse load on the pavement surface. The data are commonly used in models for backcalculation of elastic moduli and strains. More complex modeling would involve finite element or dynamic element methods. The FWD method has proven to be an excellent tool for overlay design. For this purpose its simplicity and straightforwardness are well documented. However, to successfully backcalculate layer stiffness adequate layer thickness is needed. Thus there is a strong need for assessing layer data at testing points. Using Ground Penetrating Radar (GPR) it is possible to achieve data without coring. The present paper is a part of an ongoing bearing capacity study carried out by a regional road administration in central Sweden. Its objective is to optimize testing for equipment and methods used and presently available. In addition to evaluate the results from the study, the present paper discusses some other applications for GPR that may evolve from it.

Using ground penetrating radar for assessing highway pavement thickness

Pavement deflection is the primary indicator reflecting road-bearing capacity. The falling weight deflectometer (FWD) and the Benkelman beam deflectometer (BBD) are widely used in deflection measurement, and are suitable for measuring the elastic deflection of pavement under static loading or dynamic impact loading. In recent years, there has been an increasing interest in continuous dynamic deflectometers, especially velocity-based deflectometers. The velocity-based continuous dynamic deflectometers, such as the laser dynamic deflectometer (LDD), are used to solve the problems of traffic speed and non-destructive pavement deflection measurement. However, there can be many deviations caused by the varied environmental parameters in practical application. In this article, through the review of the mechanism of the Euler-Bernoulli beam upon an elastic foundation and the corresponding influencing factors, the internal and external factors causing dynamic deflection measurement deviation are analyzed and summarized. The influences of pavement temperature, vehicle speed, pavement condition, and other factors are summarized and discussed. On this basis, a model of environmental parameter correction for the continuous dynamic deflectometer is established using a regression analysis method. Numbers of experiments confirmed the reliability of the correction model under different measurement conditions. The correlation experiments between the LDD and different types of deflectometer confirmed the accuracy of the correction model under different measurement conditions. The results showed that the correction model for the continuous deflection measurement of pavements under dynamic loads has strong robustness in different environments and conditions.

/pdf/a-correction-model-for-the-continuous-deflection-measurement-2s8edn82e9.pdf

A Correction Model for the Continuous Deflection Measurement of Pavements Under Dynamic Loads

The high-speed road deflection tester

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/pdf/pavement-structural-evaluation-using-the-rolling-wheel-4jsu7vap0r.pdf

Pavement structural evaluation using the Rolling Wheel Deflectometer

The Road Deflection Tester (RDT) is a testing vehicle for highways capable of assessing a road deflection profile at traffic speeds by using two arrays of laser range finders. The deflection profile in turn is evaluated to determine layer properties in the road structure. The present study looks at some geometric relationships that can be used for this purpose. It was found that evaluation techniques used for stationary devices are less suitable. Other methods may however, be of great value.

Evaluating pavement layer properties with a high-speed rolling deflectometer

Forty laser range finders mounted on a truck are used to assess two transverse profiles. One profile constitutes an unloaded case; it is placed 2.5 m behind the front wheel axle where the road is little influenced by any vehicle load. The other profile, .50 m behind the rear axle of the vehicle, constitutes the loaded case. This paper is an evaluation of the different profiles gathered on four different locations. In this context, a correlation with the subgrade elastic properties derived from backcalculation of falling weight deflectometer (FWD) data is sought. Correlation with other layers have been analyzed and will be published.

Carl A. Lenngren

Papers

Evaluating pavement layer properties with a high-speed rolling deflectometer

Evaluating subgrade properties with a high-speed rolling deflectometer