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Submerged Road Characteristics and Distresses on LA 493, Natchitoches Parish, State Project Number H.011071
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Submerged Road Characteristics and Distresses on LA 493, Natchitoches Parish, State Project Number H.011071
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    Technical Assistance Report, August to November 2017
  • Abstract:
    The Louisiana Transportation Research Center (LTRC) is conducting a research project to determine the pavement and embankment distress mechanisms associated with normal seasonal variation changes in the subgrade soil and base course moisture content in areas with and without trees. Approximately two months after the newly constructed asphaltic concrete roadway was fully opened to traffic, it was submerged for several months (January 2016 to March 2016) due to a heavy rainfall event. Since that time, it was submerged twice more from February 2017 to April 2017 and July 2017 to August 2017. Submergence events created higher subgrade soil and base course layer saturation events beyond the “normal” seasonal variation in those layers based upon LTRC’s knowledge. Because of that, the original experiment was adjusted to accommodate the submergence events. The damage to the pavement structure in the six test sites caused by the submergence events could now be catalogued on a newly constructed pavement during the time period of December 2015 to July 2018. A cross-section survey was conducted in December 2015 approximately one month prior to the first submergence event (January 2016). Subsequent cross-section surveys were conducted. The test sites were assessed with LTRC’s roadway surface profiler and imaging system on June 2017 and June 2018. Information from the profiler and imaging system provided information on the roughness of the roadway as measured by the International Roughness Index (IRI), roadway surface profile, roadway surface rutting, and roadway surface cracks. With these parameters inferences were made on the damage caused by the submergence events. Cross-section surveys clearly demonstrated the elevation increases and differential movements across the pavement surface caused by the submergence event(s). The increase in elevation at the centerline of the roadway ranged from 2.44 mm to 44.50 mm. With the exception of cross-section Site 1A, cross-section points right and left of the centerline all increased with no adjacent point having the same magnitude of increase within each cross-section. This in and of itself will cause damage to the entire roadway section (pavement and soil cement base course). The differential movements in the cross-sections occurred to varying degrees at the different test sites as observed on subsequent cross-section surveys. Movements of differing proportions throughout the service life of the pavement will adversely affect its performance and reduce its service life. The data gathered from the profiler and imagining system also provided evidence of damage caused by submerging the newly constructed pavement. On the June 2017 assessment, the maximum IRI was 141.8 and the minimum was 84.7 for both travel lanes in the test sites. At that time the pavement had been in service for approximately 19 months of which it was submerged for 3 months. When the new roadway was fully opened to traffic, it is reasonable to assume that the roadway had no surface cracks or rutting and that the IRI would have been less than or equal to 75 in./mile, which is the Louisiana Department of Transportation and Development's (DOTD’s) IRI requirement for this type of newly constructed roadway. With that being the case, IRI values as high as 141.8 greatly exceeds the IRI values that should have been present on a low volume roadway at this point in its service life. On the June 2018 assessment, the IRI values ranged from 176.5 to 75.2. There was a slight increase in roughness between the 2018 and 2017 assessment period which was to be expected. The high variability in IRI magnitudes observed in the test site locations which were a total length of 4,702 ft indicate that significant differences in the longitudinal profile existed. Plots of the longitudinal profile confirmed this. The rutting data also pointed towards damage in the roadway structure. There was a high variability in rutting amongst the test sites. Rutting values as high as 42.8 mm were measured. Regarding roadway surface cracking, only longitudinal cracks were observed on the test sites. The observed longitudinal cracks in the test sites ranged from 3 ft to 1,003 ft and 16 ft to 1,017 ft, respectively, on the June 2017 and 2018 assessments. The amounts of longitudinal cracks observed indicated that (1) most of the sites had excessive longitudinal cracking for the time that they were in service, (2) the longitudinal cracking observed is consistent with volumetric changes occurring in the subgrade, and (3) it is logical to infer that the submergence events were responsible for both the magnitude and premature emergence of these longitudinal cracks.
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