Near Geogrid Stiffness Quantification in Airport Pavement Base Layers Using Bender Element Field Sensor

Transportation Research Record: Journal of the Transportation R

et al. 2023

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The progressive degradation of railway ballast over time increases the degree of ballast fouling and poses significant drainability concerns leading to frequent maintenance activities. To avoid such issues, an effective and continuous characterization of the physical properties of the ballast layer is deemed necessary. This paper introduces the combined use of a bender element (BE) piezoelectric field sensor and a PANDA® dynamic cone penetrometer for periodic evaluations of ballast condition over the traffic use. To simulate various levels of ballast degradation, box tests were conducted using a dolomitic ballast material compacted in a laboratory-sized testbed with fouling indices ranging from zero to 39%. BE sensor pairs were embedded in the ballast layer to calculate the small strain modulus behavior of the ballast assessed through shear wave velocity measurements under different confinement conditions. Strength profiles of the ballast at different fouling levels were also measured using the PANDA® penetrometer. Experimental findings from both test methods indicate the existence of a dense state of ballast linked to a certain fouling index that maximized stiffness and strength characteristics of the tested ballast in dry condition. Accordingly, the potential use of BE field sensors embedded within in-service ballasted track coupled with periodic penetration testing can be a viable approach to evaluate ballast layer degradation. Various void packing conditions associated with ballast fouling levels can be linked to important ballast layer modulus and strength behavior. Further, such smart sensing of ballasted track behavior can provide long-term performance monitoring solutions for ballast cleaning and maintenance scheduling.

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confidence: 99%

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

Transportation Research Record: Journal of the Transportation R

et al. 2023

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“…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).…”

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confidence: 99%

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

Transportation Research Record: Journal of the Transportation R

et al. 2023

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Real-time stiffness monitoring of unbound aggregate layers using embedded field sensors is crucial for advanced airport pavement design and management. This paper describes research findings on monitoring base layer stiffness characteristics for airport pavements using an embedded bender element (BE) field sensor, inductive coil sensors, and pressure cells. A full-scale pavement test section was constructed at the Federal Aviation Administration (FAA)’s National Airport Pavement Test Facility (NAPTF). A BE field sensor, inductive coil sensor pairs, and pressure cells were installed in the unbound aggregate base to evaluate the layer stiffness, applied load stress, and deformation characteristics. A triple dual tandem gear loading module applied 58,000 lb per wheel to the tested section with a wander pattern consisting of 66 passes arranged in nine lateral wander positions. Dynamic responses of coil sensors and pressure cells were collected during the traffic test, whereas BE signals were collected after completing each wander pattern. Laboratory repeated load triaxial tests with BE instrumentation were also conducted to establish a correlation for converting BE field sensor readings to layer modulus properties. The in situ modulus characteristics of the aggregate base layer were evaluated during full-scale testing using two methods: shear wave velocities from a BE field sensor, and strain and stress measurements from coil sensors and pressure cells. The moduli estimated using both approaches fell into typical ranges of crushed aggregate bases and were highly comparable. The moduli from the dynamic sensor measurements clearly showed the effect of vehicle wander on aggregate base layer measured responses.

“…Shear wave transducers are commonly used in geotechnical applications to characterize the soil modulus through shear wave velocity measurements. Recent research efforts have demonstrated an innovative use of shear wave transducers, in the form of bender element (BE) sensors, to assess the small-strain modulus behavior of construction aggregates both in laboratory test set-ups and field installations (11)(12)(13)(14)(15)(16). Given that BEs can be embedded in unbound aggregate layers at any desired location and orientation, they can provide direct and quantitative evaluations of local stiffness enhancements caused by geogrid-aggregate interlock.…”

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confidence: 99%

Evaluation of Open-Graded Aggregates Stabilized with a Multi-Axial Geogrid Using a Large-Scale Triaxial Test Set-Up

Transportation Research Record: Journal of the Transportation R

et al. 2023

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Geogrids are commonly used in paved and unpaved roadways to stabilize base and subbase layers by laterally restraining movements of unbound aggregates under applied wheel loading, often referred to as interlocking. The geogrid-aggregate interlock is a function of the match between the geogrid aperture size and geometry and the grain size and shape characteristics of the stabilized aggregates. Open-graded coarse aggregates (OGA) are commonly used as an alternative to dense-graded materials in permeable base/subbase applications as well as in railway ballast to facilitate drainage. This paper describes an experimental study recently conducted to investigate the repeated load-deformation behavior of a geogrid-stabilized OGA material in large-scale triaxial testing. Two multi-axial geogrids with the same aperture patterns but different aperture sizes were tested. The aperture patterns include different sizes of hexagonal, trapezoidal, and triangular openings. The multi-axial geogrid with the larger apertures better matched the OGA material properties to provide a reduction in permanent deformation in the test specimen. The improved interlocking and the related local stiffness enhancement were successfully quantified using embedded shear wave transducers termed bender elements. To stabilize aggregates with relatively uniform grain sizes, for example, AASHTO No. 57 stone studied here and railroad ballast, the ratio between the aperture size and a representative particle size (i.e., D90) served as a good indicator of the effectiveness of the geogrid. The findings of this experimental study therefore provided valuable information on the governing properties and mechanisms that play a role in geogrid-aggregate interaction with multi-axial geogrids.