Continuous Deflection Profiles Research Articles

Physical modeling of buried PVC pipes overlying localized ground subsidence

The last half-century has witnessed a proliferation in the use of polyvinyl chloride (PVC) pipes in civil engineering applications. However, little physical data are available to date to assess conformance with performance limits of these pipes subjected to events involving localized ground subsidence. In this study, experimental results are generated and evaluated from a series of physical models involving a buried PVC pipe overlying a localized subsiding bedding zone. Ground subsidence was simulated using a precisely controlled trapdoor system positioned at mid-length of the pipe. A technique including the use of a custom-made displacement transducer was developed as part of this study to facilitate collection of continuous deflection profiles along the axis of the pipes. The progressive development of soil arching was also monitored using earth pressure sensors placed on the top, sides, and at several locations beneath the pipe, both within and beyond the zone of ground subsidence. Strains in the external wall of the pipe were also monitored. The results indicate that significant bending developed in the portion of the pipe traversing the subsidence zone, especially at the pipe crown. Beyond this point, radial deflections of the pipe cross section continued to be detected along the pipe length to distances of approximately four pipe diameters. Ground subsidence induced a severe redistribution of the earth pressures measured in the soil mass surrounding the pipe. A significant increase in vertical soil pressures beneath the pipe was captured within a distance of about one pipe diameter outside the subsidence zone. The overall response of the PVC pipe to localized ground subsidence was found to improve with increasing backfill density and decreasing soil confinement.

3D simulation of deflection basin of pavements under high-speed moving loads

The nondestructive testing of pavements currently has become more focused on continuous deflection profiles and vehicle moving speeds, which are recognized to be critical in obtaining complete and accurate pavement responses and conditions. However, current techniques cannot produce satisfactory results in terms of continuous deflection profiles at high-speed moving loads. Under this circumstance, the computational simulation is a good alternative. The objective of this study is to utilize the three-dimensional (3D) finite element (FE) analysis to investigate the characteristics of deflection basins of pavements under high-speed moving loads. Specifically, a 3D FE pavement model is constructed with six sets of pavement materials representing six types of pavements and four moving speeds (24 km/h, 40 km/h, 64 km/h, and 80 km/h). The results demonstrate that the deflection basin of a pavement exhibits an asymmetric shape under a high-speed moving load. It also reveals that there is a time lag between the maximum deflection and the center of the load in flexible pavements. This time lag is utilized to define a new term of “lag angle”. The effects of the material viscoelasticity, structural inertia damping, moving speed, and pavement deterioration conditions on the shape and lag angle of the deflection basin are illustrated. Furthermore, it is found that the lag angle of the deflection basin is closely related to the phase angle of the viscoelastic pavement materials. Finally, the deflection basins predicted by the 3D FE analysis are proven to be comparable to the field deflections obtained at a high moving speed.

Effect of daily temperature variations on the continuous deflection profiles of airfield jointed concrete pavements

Compared with highway roads primarily damaged by repeated vehicle loads, airfield pavements suffer more from heavier aircraft loading, along with environmental factors. In particular, a pavement temperature is one of the critical factors affecting the behavior and response of airfield jointed concrete pavements (JCP). Temperature variations cause curling and expansion/contraction of a slab, which may ultimately influence the in-situ deflection measurements. Along with the pavement temperature, it is well known that other parameters such as subsurface conditions (i.e. stiffness of base/subbase layers), setting temperature of concrete, slab dimensions, and joint/crack width also affect the behavior and response of JCP. The main objectives of this paper are to characterize: (1) the behavior of airfield JCP due to temperature variations in terms of pavement “deflections” (defined as the dynamic movements of a pavement induced by dynamic loading); and (2) the effects of various affecting parameters on the vertical displacement profile of JCP slabs. The primary research means include in-situ pavement deflection measurements at different times of a day. For this purpose, a rolling dynamic deflectometer (RDD) which measures the continuous deflection profiles along a selected pavement section (100% coverage of a tested path) was employed. Also, extensive two-dimensional numerical simulations were performed to provide supporting evidence for the behavior trends generated by RDD.

Field Experiences with RDD and Overlay Tester for Concrete Pavement Rehabilitation

Since reflective cracking is related to both the existing pavement condition and the overlay material, appropriate tools are needed to characterize both properties. The rolling dynamic deflectometer (RDD) was employed to measure the continuous deflection profiles that relate to vertical movements of the underlying joints and cracks. An overlay tester (OT) was utilized to characterize the asphalt mix’s ability to resist reflective cracking. The reported threshold values were employed in the study that include: (1) W1–W3=6.5 mils for composite pavement with old asphalt concrete (AC) overlay; (2) W1–W3=5.5 mils for exposed concrete pavement; and (3) 700 cycles of the OT were employed to evaluate six field rehabilitation projects (SH12, IH20, US96, SH73, SH225, and IH44). It was found that although there were severe transverse cracks and spalling on US96, all W1–W3 deflections were less than 5.5 mils , indicating low risk for reflective cracking. A stone-mastic asphalt (SMA) layer was placed 3 years ago and t...

Monitoring Pavement Changes in a Rehabilitation Project with Continuous Rolling Dynamic Deflectometer Profiles

The success of a rehabilitation project that involves replacement of the asphalt concrete (AC) overlay on a concrete pavement often depends on the assessment of the existing conditions and the repair of critically weak locations. In a case study, a rolling dynamic deflectometer (RDD) was used to collect continuous deflection profiles at different stages in such a project. The project, conducted by the Texas Department of Transportation, was located in the Atlanta District. The condition of the pavement was monitored with an RDD in each stage. The stages ranged from before milling of the original AC overlay to 22 months after the placement of a new overlay. The deflection profiles measured after milling were used to identify locations with a high potential for reflection cracking. After the new overlay was placed, profiling was repeated at three different times to ( a) monitor changes at locations of previously high deflections, ( b) evaluate the effectiveness of full-depth repairs, and ( c) group different AC test sections of the new overlay according to the condition of the underlying concrete pavement. It was found that the continuous deflection profiles obtained at the start of a rehabilitation project can be used to identify high-deflection locations that, if not repaired, will likely deteriorate rapidly after the new overlay is placed. The continuous deflection profile measured on the concrete pavement after milling was particularly helpful in identifying high-deflection locations that were irregularly spaced. Continuous deflection profiles, measured at various times after placement of the new overlay, effectively tracked the zones of deterioration.

Part 1: Pavement Rehabilitation: Monitoring Pavement Changes in a Rehabilitation Project with Continuous Rolling Dynamic Deflectometer Profiles

The success of a rehabilitation project that involves replacement of the asphalt concrete (AC) overlay on a concrete pavement often depends on the assessment of the existing conditions and the repair of critically weak locations. In a case study, a rolling dynamic deflectometer (RDD) was used to collect continuous deflection profiles at different stages in such a project. The project, conducted by the Texas Department of Transportation, was located in the Atlanta District. The condition of the pavement was monitored with an RDD in each stage. The stages ranged from before milling of the original AC overlay to 22 months after the placement of a new overlay. The deflection profiles measured after milling were used to identify locations with a high potential for reflection cracking. After the new overlay was placed, profiling was repeated at three different times to (a) monitor changes at locations of previously high deflections, (b) evaluate the effectiveness of full-depth repairs, and (c) group different A...

Discrete and Continuous Deflection Testing of Runways at Hartsfield Atlanta International Airport, Georgia

The measurement of deflection characteristics is a key feature in the evaluation of pavements. Deflections are used to evaluate pavement moduli, relative stiffness, load transfer, and, when used periodically, a rate of deterioration and remaining life. The comprehensive deflection testing program conducted on Runways 9L/27R and 8R/26L, both jointed concrete pavements, at the Hartsfield Atlanta International Airport is described. A heavy-weight deflectometer was used to measure deflections at discrete locations on slab interiors, transverse joints, longitudinal joints, and slab corners. A rolling dynamic deflectometer was used to measure continuous deflection profiles along three longitudinal lines on both runways. Before fall 2001, all pavement deflection testing was performed using a falling-weight deflectometer. Comparisons of the equipment, loading mechanisms, and measured deflections are presented.

Evaluating Runway Pavements at Seattle-Tacoma International Airport: Continuous Deflection Profiles Measured with the Rolling Dynamic Deflectometer

The rolling dynamic deflectometer (RDD) is a relatively new tool for assessing the condition of pavements. Continuous deflection profiles, rather than deflections at discrete points, are measured with the RDD. The results of RDD tests on two runways at the Seattle-Tacoma International Airport (Sea-Tac) are presented. These results illustrate how continuous deflection profiles can be used to assess the condition of pavements without the use of backcalculation. Continuous deflection profiles allow sections of pavement exhibiting large or anomalous deflections to be quickly and easily identified. The extent to which pavements are damaged and degraded can be determined by comparison of the deflections of intact, lightly trafficked pavements with the deflections of the pavements in question. The condition and load transfer capacity of all transverse joints and cracks in rigid pavements can be determined by observation of the measured deflections as the RDD approaches and crosses each joint or crack. The RDD is a valuable tool for rapidly identifying regions of pavement requiring rehabilitation. Critical regions of pavement identified with the RDD for possible rehabilitation can be studied further with use of traditional discrete testing methods. These capabilities make the RDD a valuable tool in airfield pavement management.

Profiling Flexible Highway Pavement Continuously with Rolling Dynamic Deflectometer and at Discrete Points with Falling Weight Deflectometer

Nondestructive testing of pavements plays an important role in the management of pavement infrastructure. Nondestructive testing techniques have been widely utilized in the United States during the past decade to characterize pavement systems at discrete points. Discrete-point testing is, however, not feasible for routine use as a means of continuously characterizing pavement systems. A new nondestructive testing technique for continuously profiling pavements has been developed, namely, the rolling dynamic deflectometer (RDD). The RDD is a large truck on which a servohydraulic vibrator is mounted. The vibrator is used to apply large vertical dynamic loads to the pavement with loading rollers, and the induced dynamic displacements are measured at multiple locations with rolling sensors. This arrangement permits continuous measurements at multiple locations on the pavement surface in a fraction of the time required for typical discrete-point testing at a few points along the section. In this paper, the configuration of the RDD and the procedure used to analyze RDD data are discussed. Continuous deflection profiles are presented from a test section of a flexible Interstate highway pavement, which contains several distinctly different pavement structures. The effects of the structures on measured deflections are discussed, and the capability of the RDD to delineate the extent of each feature is presented. The importance of loading frequency and resonances in the pavement structure is shown. In addition, results from the RDD are compared with results from falling weight deflectometer (FWD) tests performed at the same locations.

Continuous Profiling of Runway and Taxiway Pavements with Rolling Dynamic Deflectometer at Dallas–Fort Worth International Airport

The rolling dynamic deflectometer (RDD) is powerful tool for use in managing airport pavements. With the RDD, continuous deflection profiles of runways and taxiways can be efficiently and effectively measured. These continuous profiles, both in the longitudinal and transverse directions, provide valuable information about the condition of the pavement system. The profiles are especially valuable because the entire pavement is tested and characterized rather than approximating the system with a limited number of discrete measurements to represent the entire pavement. The capabilities of the RDD were demonstrated by testing pavements at Dallas–Fort Worth International Airport. One existing runway, one existing taxiway, and a newly constructed (but not yet opened) runway were tested. The conditions of the different intact pavement sections and the various pavement joints are readily shown in the measured deflection profiles. In most cases, heavily trafficked pavement sections showed higher deflections than comparable sections with lower traffic, with the lowest deflections measured on the newly constructed runway. However, one recently constructed runway extension showed unusually high deflections, especially at the joints. The taxiway that was tested generally exhibited lower deflections than the operating runway. In the cases of the in-service pavements, transverse profiles clearly showed the softening of the highly trafficked central portion of the pavement.