Airport Pavement Stiffness Monitoring and Assessment of Mechanical Stabilization using Bender Element Field Sensor

Abstract

The bender element (BE) field sensor is a newly developed embedded pavement instrumentation that measures shear wave velocity to estimate constructed layer moduli of unbound aggregate bases and subbases. This paper presents findings related to monitoring stiffness characteristics of airport pavement base courses instrumented with BE field sensors and tested under full-scale accelerated pavement testing during Construction Cycle 9 (CC9) of the National Airport Pavement Test Facility (NAPTF) by the U.S. Federal Aviation Administration (FAA). The CC9 aggregate base courses were constructed following FAA’s P-209 specification for a geosynthetic experiment using a biaxial geogrid installed at the bottom of the 8-in. (203-mm) thick base in the north test section, while the control pavement in the south test section was built without a geogrid. Two BE field sensors were installed in the north and south test sections approximately 1 in. (25 mm) above the base–subbase interface. Multiple stages of aircraft gear loads, including static dual-gear, dynamic slow-roll (moving wheel), and dynamic proof-roll, were applied to the test sections. BE field sensor data collected throughout multiple loading stages were used to investigate the stiffness characteristics of the pavement base. These preliminary tests conducted at the NAPTF CC9 experiment revealed the effects of static and dynamic aircraft gear loads on the stiffness of the aggregate base layer and how confinement influenced the moduli of the geogrid-stabilized base. Further, previously observed anti-shakedown effects caused by vehicle load wander could be quantified through changing base course modulus and deformation behavior from the BE field sensor data analysis.

Evaluation of Airport Pavement Base Layer Stiffness Characteristics via Embedded Field Sensors

“…The modulus of the base layer significantly drops after the first wander sequence. Such loss is likely because of particle rearrangement, which is the most significant after the initial wander, as reported from the pre-traffic testing of NAPTF CC9 test items ( 10 ). After this drop, the modulus was gradually recovered up to 10,000 cycles of repeated wheel passes.…”

“…The previous NAPTF full-scale pavement tests reported that the vehicle passes with wander offsets caused an “anti-shakedown” effect in the unbound aggregate layer because of the upward dilative deformation caused by large horizontal stresses ( 5 – 8 ). Further, Kang et al observed a modulus decrease after the wheel pass with the wheel offset and a modulus increase after the wheel pass without the wheel offset via BE field sensor measurement ( 10 ).…”

“…In addition to the deflection behavior, real-time measurements of pressures and deformations using embedded sensors enable the estimation of in situ moduli. Recent research efforts on embedded shear wave measurement sensors, termed the bender element (BE) field sensor, have shown the capacity for accurate and direct quantification of unbound aggregate stiffness, both in a laboratory setup and in full-scale field test sections (9)(10)(11)(12)(13). Laboratory repeated load triaxial tests with embedded BEs can establish the linkage between the small-strain elastic modulus and in situ M R , the field moduli assessment of which can be achieved solely by BE sensor measurements (14).…”

Degraded Ballast Stiffness Characterization Using Bender Element Field Sensor and PANDA® Penetrometer

“…The BE field sensor was recently developed to characterize the stiffness characteristics of unbound aggregate layers in road and airport pavements and are actively utilized in pavement test sections ( 17 , 18 ). The sensor utilizes a pair of BE piezoelectric shear wave transducers, widely used for granular materials on account of their great coupling ability ( 23 ).…”

“…A pair of bender element (BE) shear wave transducers can be made a field sensor, as recently developed for embedding in unbound aggregate layers of road and airfield pavements, to measure shear wave velocity of the granular medium and estimate layer stiffness characteristics. Multiple applications of BE field sensors both in laboratory and in full-scale field installations have been proposed and successfully demonstrated with validated sensor capabilities for measuring shear wave velocity accurately for a direct quantification of unbound aggregate layer stiffness (17)(18)(19)(20). However, such a BE field sensor has not yet been applied to the large and uniformsized railroad ballast.…”