SPA Application: Pavement Maintenance and Rehabilitation

In recent years, the focus of pavement engineering has shifted from design and construction of new highways to preventive maintenance and rehabilitation of existing highways. A highway maintenance program is usually based on a visual condition survey and, to a lesser extent, on appropriate in situ tests. By the time symptoms of deterioration are visible, major rehabilitation or reconstruction is often required. If the onset of deterioration can be measured accurately in the early stages, problems can often be resolved or stabilized through preventive maintenance.

Recent studies by a number of organizations have shown that the seismic methods can provide more reliable information about the properties of the pavement layers above the subgrade. This feature makes seismic methods a prime tool for objectively determining the structural deficiencies associated with existing pavements.

Case Studies of Pavement Maintenance and Rehabilitation

A Rapid Approach to Interpretation of SASW Results
H. Wu, S. Wang, I. Abdallah & S. Nazarian
Center for Highway Materials Research
The University of Texas at El Paso
El Paso, Texas USA


Nondestructive testing (NDT) of pavements has made substantial progress during the last two decades. Most algorithms currently used to determine the remaining life of pavements rely on stiffness parameters determined from NDT devices. One major area of continual improvement is the reliable extraction of stiffness parameters from nondestructive field data. The Spectral Analysis of Surface Waves (SASW) method is one of the NDT methods that is used more frequently because of its capabilities in characterizing the near-surface layers more effectively. In this method, time records obtained with vibration sensors are used to obtain an experimental dispersion curve, which provides, through an inversion procedure, an estimate of the elastic modulus profile of the pavement. The inversion process requires a significant computational effort or frequent operator’s intervention. To improve the user-friendliness of the inversion process, a new algorithm for the rapid reduction of the SASW data has been developed. Thickness and modulus of each pavement layer are estimated in real time using artificial neural network models. The training and validation of models are done using an axisymmetrical full-waveform forward model to minimize the approximations associated with simpler models used in the inversion algorithms.

This paper provides an overview of the proposed inversion and its practical use and limitations in pavement analysis and design. The reduction algorithm seems to be robust and to yield consistent results in almost real time.

Use of Seismic Methods in Monitoring Pavement Deterioration During
Accelerated Pavement Testing with TxMLS

Soheil Nazarian, Deren Yuan
Center for Highway Materials Research, University of Texas at El Paso, TX 79968-0516

Darhao Chen and Mark McDaniel
Design Division, Texas Department of Transportation Austin, TX 79932


Seismic methods have been used in conjunction with an accelerated pavement testing (APT) program under the Texas Mobile Load Simulator (TxMLS) to monitor the variation in pavement condition with the number of axle repetitions applied to four test pads. The modulus of each layer, especially the surface asphalt concrete layer, and the overall stiffness of a pavement structure at different stages of TxMLS loading are the major parameters estimated with seismic methods in this case. The results from seismic tests are compared with those from other nondestructive tests as well as cracking and rutting surveys. The feasibility of using seismic nondestructive technology in predicting and monitoring of degradation of pavements was confirmed with this experiment.

Most of the seismic tests were carried out with two nondestructive testing devices, the Seismic Pavement Analyzer (SPA) and its hand-portable version (PSPA). The SPA combines several seismic testing techniques in a single unit and can rapidly perform tests to determine the condition of a pavement structure. The PSPA is used to detect the variation in modulus of the top pavement layer
(AC) at each test pad. The theoretical background of the seismic methods, as well as the SPA and PSPA are briefly described. Recent advancements and issues in terms of real-time implementation of seismic methods in the accelerated pavement testing programs are discussed. In general, the seismic methods seem to provide information that can be utilized in better understanding the mechanism of failure of pavements.

Geomedia SPA Application: Pavement Maintenance and Rehabilitation