Backcalculating Pavement Layer Moduli as a Function of Traffic Speed Deflections

The current engineering practice for backcalculating pavement layer moduli is mostlydependent on the Falling Weight Deflectometer (FWD) deflection measurements. The FWD is a commonly used non-destructive testing (NDT) technique that plays a significant role in the process of evaluating the structural conditions of pavement structures. The backcalculated moduli can be used to estimate the pavement responses under traffic loading, evaluate the load carrying capacity, estimate the remaining life of in-service pavements, devise an appropriate maintenance/rehabilitation strategy for deteriorated pavement structures, and monitor the structural health of existing pavements. The FWD test is typically performed by dropping a certain load from a specific height, and a set of geophones at several radial offsets are used to measure the pavement responses due to the applied load pulse. Then, the deflection basin (i.e., surface deflections at lateral distances where the geophones are placed) resulted from the FWD test is used to backcalculate the pavement layer moduli. The FWD currently enjoys a worldwide acceptance among engineering professionals with a proven record of yielding acceptable moduli values for the different pavement assessment applications. However, due to the stationary nature of the test, there are some challenges associated with the testing technique that make it infeasible for monitoring the pavement structural conditions on the network level. Recently, some commercial companies have developed equipment capable of measuring the pavement surface deflections at traffic speeds. These devices are known as the traffic speed deflection devices (TSDDs). The main advantages of these newly introduced TSDDs are theirvi versatility and capability of being used for monitoring the pavement health conditions on the network level without interrupting the traffic, whist being feasible in terms of the cost and required time for testing protocols. This research study was focused on the Dynatest's RAPTOR to develop a new methodology for backcalculating the pavement layer moduli of existing pavement structures as a function of traffic speed deflections collected by the RAPTOR. However, the methods used in this study can be replicated for the use with any other TSDD or it can be generalized to include all the TSDDs available in the market. The methodology used in this research study was based on developing a finite element model that can be used as a forward solution to predict the pavement structural response under the RAPTOR loading. Then, the developed model was used to generate a traffic speed deflection database that was used with different modeling techniques to provide a pavement layer moduli backcalculation model. The developed methodology was validated against both field and lab data and it was concluded that the developed models can yield acceptable accuracy for backcalculating the layer moduli as a function of traffic speed deflections.