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

APPENDIX J. FWD SN #061, JULY 17, 1995–OCTOBER 31, 1995

This previously reported sensor position error was located in the database using an automated screening version of SLIC. This screening version is tailored for sensor 7 (among others), with a close to zero overall bias and the best possible precision (see appendix B). The first graph shown in this appendix (figure 44) is a plot of all the SN #061 values for the d7 sensor position predictions from November 1994 through March 1997, for all lane 1, drop height 4 FWD tests.

In figure 44 it can be seen that the average prediction for this 2-year plus period, excepting the data for the dates in question, was around 152.4 cm (60 inches), as expected. The predictions are somewhat scattered, mainly due to the relatively large distance of d7 from the loading plate when in its protocol position (152.4 cm (60 inches)). However, during the period of time in question (July 17, 1995 to October 31, 1995), the average predicted position of d7 is clearly around 121.9 cm (48 inches) (average SLIC prediction for all flagged test dates = 119.9 cm (47.2 inches)). In fact, an empty Dynatest sensor holder should have been positioned at 121.9 cm (48 inches) during this period of time.

In the second figure in this appendix (see figure 45), it can clearly be seen that the SN #061 predicted positions for sensor 7 for the dates in question are outliers relative to the predicted positions for sensor 7 when correctly configured FWDs are used. Once again, the prediction for the position of sensor 7 is close to 121.9 cm (48 inches). For the seven test sections shown (from three different FWDs), on average the predicted position of d7 was 148.3 cm (58.4 inches), while the same prediction for SN #061 during the period of time in question was 118.4 cm (46.6 inches).

In the two following figures in this appendix, figures 46 and 47, the same results are shown graphically, with the light gray lines and data points showing the SLIC plots for d7 in both its actual (121.9 cm (48 inches)) and incorrect (152.4 cm (60 inches)) offset positions. The portions of the light gray lines that are parallel to the rest of the lines are the correct plots, with d7 set to 121.9 cm (48 inches). In one of these two cases (figure 47), it can also be seen that the data includes another sensor spacing error for SN #061, namely the 1989 error covered in appendix F. In this case, the SLIC-determined metric sensor positions have been used, which, when transformed, correctly plots the data for section 32–7000 on a parallel line, for FWD tests conducted on May 5, 1989 (in this case with black lines and data points).

Because of this information, and the previous information supplied to FHWA, it can be concluded with certainty that d7 was not positioned correctly at 152.4 cm (60 inches); rather, it was positioned at 121.9 cm (48 inches) (or very close to 121.9 cm (48 inches)) on FWD SN #061 between July 17, 1995, and October 31, 1995. These dates correspond to the dates when lane 1 tests were conducted at drop height 4. This period of time may need to be extended slightly, if other tests were conducted along different lanes or at different drop heights. In any case, FWD tests conducted on or before March 31, 1995, and on or after November 14, 1995, clearly show d7 positioned at 152.4 cm (60 inches) (per protocol).

Figure 44. Graph. Predicted position of D7, unit 061, 1994 to 1997. The figure is a scatter plot showing all serial number 061 D7 sensor position predictions for the period November 1994 through March 1997. The X-axis is the number of the observation and ranges from one to approximately 250. The Y-axis is the predicted position of sensor D7 in inches and ranges from 35 to 80 inches parenthesis 88.9 to 203.2 centimeters end parenthesis. With the exception of observations that fall in the period July to October 1997, the sensor predictions, although somewhat scattered, are generally between 50 and 75 inches parenthesis 127 and 190.5 centimeters end parenthesis. For the period July to October 1997, most of the observations are between 45 and 50 inches parenthesis 114.3 and 127 centimeters end parenthesis.

Figure 44. Graph. Predicted position of d7, unit #061, 1994–97.

Figure 45. Graph. Same section data for D7 position, three different falling weight deflectometers. The figure is a scatter plot illustrating predictions of D7 for three falling weight deflectometers, including serial number 061. The X-axis is the date of testing and ranges from August 30, 1989, to November 16, 1997. The Y-axis is the predicted position of sensor D7 in inches and ranges from 40 to 80 inches parenthesis 101.6 to 203.2 centimeters end parenthesis. With the exception of the testing by FWD serial number 061 in the summer of 1995, the predicted positions of D7 were predominantly between 50 and 60 inches parenthesis 127 and 152.4 centimeters end parenthesis. The average prediction for the testing by FWD serial number 061 in the summer of 1995 was approximately 48 inches parenthesis 121.9 centimeters end parenthesis.

Figure 45. Graph. Same section data for d7 position, three different FWDs.

Figure 46. Graph. SLIC plots for section 04–A310 including unit number 061, July 1995. The figure is a line graph showing the SLIC plots for falling weight deflectometer testing on section 04–A310 on five different test dates. The X-axis is the natural logarithm of the offset in inches and ranges from 2.0 to 4.5 inches parenthesis 5.2 to 11.4 centimeters end parenthesis. The Y-axis is the natural logarithm, positive or negative, of the normalized deflection, and ranges from minus 2.0 to 1.5. With the exception of the testing by FWD serial number 061 on July 18, 1995, the plots are close to linear, almost parallel to each other, and rise from left to right. The plot for the testing by FWD serial number 061 on July 18, 1995, is divided into two parts. One part, which plots the correct data, is parallel to the other plots. The other part, which plots the incorrect data, is identical to the first part for most of the first part’s length but then flattens.

Figure 46. Graph. SLIC plots for section 04–A310 including unit #061, July 1995.

Figure 47. Graph. SLIC plots for section 32–7000 including number unit 061, September 1995. The figure is a line graph showing the SLIC plots for falling weight deflectometer testing on section 32–7000 on three different test dates. The X-axis is the natural logarithm of the offset in inches and ranges from 2.0 to 4.5 inches parenthesis 5.2 to 11.4 centimeters end parenthesis. The Y-axis is the natural logarithm, positive or negative, of the normalized deflection, and ranges from minus 2.0 to 1.0. One of the three plots, that for September 13, 1991, data, is close to linear, rising from left to right. The plot for the testing by FWD serial number 061 on September 28, 1995, is divided into two parts. One part, which plots the correct data, is parallel to the plot for 9/13/1991 data. The other part, which plots the incorrect data, is identical to the first part for most of the first part’s length but then flattens. The plot for the testing by FWD serial number 061 on May 5, 1989, is also divided into two parts. One part, which plots the correct data, is parallel to the plot for September 13, 1991, data. The other part, which plots the incorrect data, is identical to the first part initially, then rises, then resumes being parallel to the plot for September 13, 1991, data.

Figure 47. Graph. SLIC plots for section 32–7000 including unit #061, September 1995.

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