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Publication Number: FHWA-RD-03-093
Date: August 2006

Study of Long-Term Pavement Performance (LTPP): Pavement Deflections

Chapter 6. Noted Anomalies and Other Potential Data Problems

Data Screening Anomalies or Spurious Data

During the process of identifying the data errors described in chapters 3, 4, and 5, other potential errors or anomalies were also identified. In most cases, however, these anomalies could not be verified or rectified; thus, they were not recommended for specific changes in the database. These unverified errors or anomalies are discussed in this chapter, in one of the two following categories:

  • General or global notes about the types of problems or spurious data encountered (some specific instances are also covered elsewhere in this report).
  • Specific notes referring to each spurious day file (day file-specific notes only).

Precautionary Notes Referring to the FWD Load-Deflection Tables

Table 7 consists of a list of the most important, general data anomalies noted during the course of analyzing the FWD load-deflection data. Some of these anomalies have been addressed in the foregoing chapters as well.

 

Table 7. General data anomaly notes of unchanged records or files.
Note 1 In all cases where unbound material tests (designated as lane S* or G*) were conducted, these data have not been recommended for changes or flags in the level E database. It should be noted that the quality and repeatability of this data is an order of magnitude or so poorer than the rest of the level E load-deflection data. Therefore, unbound material test data have not been as thoroughly screened as the remaining load-deflection data in the data tables.
Note 2 It is possible to interchange one dedicated FWD field computer for another, such as when there are two FWDs and corresponding system processors in the same region. This may or may not have occurred in practice; if so, the load and deflection readings will be affected to an unknown degree (possibly several percentage points), but such effects probably are not detectable using the available screening tools.
Note 3 In many cases, the configuration number indicates PCC joint testing positions (e.g., J4, J5, C4, or C5) as 0, 305, 305, 457, etc.; in each of these cases the value +305 denoted for d2 should be, or should already have been, changed to –305, corresponding to the position of the sensor behind the FWD loading plate.
Note 4 There were many stationing errors where the plus (+) or minus (–) sign was recorded and stored in the level E data tables opposite of what it should have been. Most, but probably not all, of these errors have been identified and recommended for change in the data tables.
Note 5 In Region 3, States 35 and 40 (New Mexico and Oklahoma), in many cases when PCC testing was conducted on different dates, there appear to be large deflection differences in the lane 1 tests from one test date to the next (up to a factor of 2 or 3, or more). Quite possibly, this could be due to liftoff or slab warping resulting from extreme thermal gradients. If so, this is a phenomenon worthy of further investigation and, possibly, altering testing protocols for jointed PCC pavement in some areas.
Note 6 In Region 2, on some of the SPS–5 sections denoted 27–050*, it was noted that the variation from date-to-date in deflections was very large. This variation may in fact have been due to an error in section identification. However, it was not possible to determine the actual cause of this potential set of anomalies. Therefore, the FWD data associated with these SPS–5 sections have not been recommended for changes or flags in the level E database. However, such anomalies or potential site/section errors could be identified with certainty by installing a low-cost global positioning system on the affected FWDs for future testing.
Note 7 In Region 4, there are a large number of PCC joint efficiencies measuring well over 100 percent; however, only those over 113 percent were noted in a separate data table. None of these has been corrected, and no data have been removed or flagged in the level E data tables.
Note 8 In Region 3, there are a small number of PCC joint efficiencies measuring over 100 percent; however only those over 105 percent were noted in a separate data table. None of these has been corrected, and no data have been removed from the level E data tables.
Note 9 In Region 2, it appears that there are many cases where the PCC joint was placed between d3 and d4 instead of d1 and d3 as per protocol, for lane J4 tests. However, only the most extreme cases of these were noted in a separate data table. None of these has been corrected, and no data have been removed from the level E data tables.
Note 10 In Region 1, it appears that there are some cases where the PCC joint was placed between d3 and d4 instead of d1 and d3, for lane J4 tests. However, only the most extreme cases of these were noted in a separate data table. None of these has been corrected, and no data have been removed from the level E data tables.
Note 11 In Region 4, section 04–0502, on all six dates of testing there was a bizarre pattern of deflection development between dates. The FWD load-deflection table results are nevertheless possible; thus no errors have been reported, and no data have been corrected, removed, or flagged in the level E data tables.
Note 12 In Region 4, section 04–0509, on all seven dates of testing for this section (intensive rehabilitation: ~50.8-mm (2-inch) overlay), the data is somewhat peculiar. Nevertheless, since FWD testing was possibly (but not definitely) conducted on the correct test section before, during, and after rehabilitation given these strange results, no errors have been reported, and no data have been corrected, removed, or flagged in the level E data tables.
Note 13 In Region 4, section 06–b420, on all four dates of testing for this section there were many test points (whether J1, J4, J5 or J6, etc.) that show strange or bizarre deflections, such as nondecreasing, too large, or too small, etc. However, not all test points were unusual; thus no errors have been reported, and no data have been corrected or removed from the level E data tables except through other procedures mentioned in other sections of this report.
Note 14 In Region 4, section 08–0214, on all three dates of testing for this section, a plausible pattern of deflection development was noticed between test dates, but the magnitudes of the deflection readings were vastly different (by as much as a factor of 3). These seem unlikely, but since the results are possible, no errors have been reported, and no data have been corrected, removed, or flagged in the level E data tables.
Note 15 In Region 4, section 08–0220, on all three dates of testing for this section, a plausible pattern of deflection development was noticed between test dates, but there were appreciable differences between dates, especially in the deflections between stations 100 and 350. Nevertheless, no errors have been reported, and no data have been corrected, removed, or flagged in the level E data tables.
Note 16 In Region 4, section 08–2008, on all dates of testing for this section, it appears that there may have been an overlay placed between May and October 1991, but the construction number remains the same throughout (CN = 1). This is probably (but not definitely) an error in the level E database value of CN, which should be considered in any subsequent data analyses conducted on the test section.
Note 17 In a handful of cases, it is possible that lane designation errors occurred during an entire day of testing, although this particular category of data errors was not specifically screened. One such instance (on two consecutive dates of test) was identified and corrected, as discussed in chapter 5 of this report.
Note 18 In the course of screening for FWD load-deflection errors and anomalies, it was noticed that some of the operator comments had not been uploaded to the database, while others were recorded for general DataPave or level E use. It is suggested that the remaining comments be uploaded together with the deflection data as both become available. Such comments often yield important information about data collection problems or anomalies that can be quite useful to the analyst.
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The Federal Highway Administration (FHWA) is a part of the U.S. Department of Transportation and is headquartered in Washington, D.C., with field offices across the United States. is a major agency of the U.S. Department of Transportation (DOT). Provide leadership and technology for the delivery of long life pavements that meet our customers needs and are safe, cost effective, and can be effectively maintained. Federal Highway Administration's (FHWA) R&T Web site portal, which provides access to or information about the Agency’s R&T program, projects, partnerships, publications, and results.
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