In Australia, the mechanical and chemical stabilization of pavement materials has been under way for more than 30 years. Recently, new polymeric-based additives have been shown to provide superior sustain-ability advantages for the construction and maintenance of low-volume roads (particularly unsealed roads) over traditional cement-blended additives. However, little quantifiable information has been published on the improved geotechnical characteristics resulting from the use of such polymeric-based additives. This paper reports on a series of uncon-fined compressive strength tests that were performed on three typical pavement material types, which were all treated with a single type of polyacrylamide additive. The compaction effort was varied at three levels (i.e., 25, 35, and 45 blows per layer with modified compaction effort). All samples were cured for 14 days prior to testing. The results of this study confirmed an increase in dry density and unconfined compressive strength for the three soils treated with the polyacrylamide additive.
A study was initiated to identify the levels and frequencies of heavy articulated vehicle body vibrations at which the drivers perceive the ride as uncomfortable. The study involved conducting a subjective assessment survey in which a panel of truck drivers were asked to rate the ride quality provided by a number of road sections with different surface roughness characteristics. The study's objective was achieved by correlating the mean panel ratings (MPRs) to road surface roughness contents in different one-third-octave bands of the roughness spectrum. The results showed that at 100 km/h, truck drivers object mainly to motions resulting from roughness excitations of the low frequency vibration modes of the truck body in the range 1.42 -5.7 Hz. These results were validated by correlating MPRs with the levels of whole body vibrations measured on the driver's seat in a representative vehicle while traversing some test sections. MPRs were found to correlate well with the measured overall vibration total values and the likely comfort reactions to various magnitudes of overall vibration total values given by ISO 2631-1. The influence on MPRs of vehicle and driver related factors were also investigated and commented upon. INTRODUCTIONThe ride environment of the truck driver is the product of the applied excitation and the response properties of the truck (Gillespie, 1985). Road surface roughness is a major source of excitation in addition to the rotating tyre/wheel assemblies, the driveline and the engine (Gillespie, 1985). When a vehicle traverses a rough road pavement, surface irregularities excite different vibration modes of the vehicle body at different frequencies. Past research has shown that heavy vehicle ride is most sensitive to excitations of the low frequency modes in the range 1-8 Hz (Gillespie, 1985). At these frequencies, modes such as body bounce, pitch, roll, frame bending and axle hop are excited. The resulting motions affect the ride quality perceived by the occupants and their comfort as at these frequencies humans are most sensitive to vertical (4-10 Hz) lateral and longitudinal (0.5-2 Hz) vibrations (IS0-2631-1, 1997).The aim of this paper is to report on the results of a study conducted for the purpose of identifying the levels and frequencies of heavy articulated vehicle body vibrations, excited by road roughness, at which the drivers perceive the ride as uncomfortable. The study involved conducting a subjective assessment survey to collect drivers' ratings of the ride quality provided by a number of road sections with varying roughness levels and spectral characteristics. Further, Whole Body Vibrations (WBV) transmitted through the driver's seat were measured at highway speed on a number of test sections.Driver's perception of ride is influenced by factors other than the vibrations present in the vehicle's cabin. They include factors related to the road, the vehicle
Road surface roughness excites low- and high-frequency vibration modes of a heavy articulated vehicle body. These vibrations result in motions in all directions that detract from the driver’s perceived ride and comfort and increase pavement damage due to dynamic wheel loads (DWLs). A subjective assessment survey was conducted to identify surface roughness characteristics that mainly influence the perceptions of heavy-vehicle drivers of pavement rideability and their comfort. The latter was achieved by correlating drivers’ ratings to roughness contents in different roughness wavebands. The results indicated that the drivers mainly object to low-frequency body vibrations excited by roughness wavelengths in the range of 4.88 to 19.5 m. Roughness content in this band was used to establish a new profile-based index called the profile index for truck ( PIt). Drivers consider pavement rideability to be poor when PIt exceeds 2.75 m/km. PIt provides better predictions of heavy vehicle ride than the international roughness index (IRI). The methodology for developing the PIt and assessment of its reliability as a measure of heavy vehicle ride are described. The latter was achieved by testing the statistical significance of the effects of factors other than road roughness that influence the perceived ride of truck drivers. They include factors related to the vehicle, the road, and the driver as well as situational factors. In addition, PIt was found to be a better indicator than IRI of the levels of whole body vibrations transmitted to the driver through the seat and a better predictor of the magnitude of DWL to which the test pavements are subject.
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