Skip to contentUnited States Department of Transportation - Federal Highway Administration FHWA Home
Research Home   |   Pavements Home
Report
This report is an archived publication and may contain dated technical, contact, and link information
Publication Number: FHWA-HRT-08-056
Date: November 2008

LTPP Manual for Profile Measurements and Processing

APPENDIX E. PROCEDURE FOR DETERMINING DIPSTICK ® FOOTPAD SPACING

Background

Testing performed in the field has indicated that the spacing between the centerline of the footpads in various Dipsticks® that are used in the LTPP program is not exactly 304.8 mm. Therefore, each RSC is required to perform a field test annually to determine the footpad spacing of each Dipstick® in their possession. This appendix describes procedures for performing the field test and the procedure for computing the footpad spacing of the Dipstick® from that data.

Test Plan

This test should be performed on a smooth AC or PCC pavement that is free of distress. Use the following procedure to layout the section and perform the test.

  1. Layout a 30.48 m long test section. Use a cloth tape that is in a good condition to layout the section. A longitudinal chalk line should be marked on the section. When marking the chalk line, extend the chalk line 0.3 m past the end on the test section. Two transverse chalk lines should be marked perpendicular to the longitudinal survey line at the start (0 m) and the end (30.48 m) of the section. Figure 99 shows the layout of the test section.

    Figure 99. Illustration. Test section layout. This figure shows the layout of the test section for determining the Dipstick  footpad spacing. The distance between the start of the section and the end of the section is 30.48 m. A longitudinal survey line is shown connecting the start and the end of the section. Transverse lines that are perpendicular to the longitudinal survey line are placed at the start and the end of the section.
    Figure 99. Illustration. Test section layout.

  2.  
  3. Measure the diameter (in mm) of each footpad in the Dipstick® using a caliper and record the values.
  4.  
  5. Place the back end of the back footpad of the Dipstick® in line with the transverse line marked at the beginning of the test section (see figure 100).

    Figure 100. Illustration. Location of back footpad of Dipstick  at start of the section. This figure shows the location of the back footpad of the Dipstick  when it is placed at the start of the section to begin measurements. The back end of the back footpad is placed such that the back end is in line with the start of the section.
    Figure 100. Illustration. Location of back footpad of Dipstick® at start of the section.

  6.  
  7. Walk the Dipstick® along the section following the procedures outlined in section 3.3.3 of this manual. After taking the 100th reading, measure the distance (in mm) from the back end of the front footpad of the Dipstick® to the transverse line that was marked at the end of the section. The following possible scenarios can occur:
    1. Back end of front footpad is past the transverse line at the end of the test section (see figure 101). The distance to be measured is the distance X indicated in figure 101. Measure this distance (in mm).
    2.  
    3. Back end of the front footpad is before the transverse line at the end of the section (see figure 102). The distance to be measured is the distance X indicated in figure 102. Measure this distance (in mm).
    4.  
    5. Back end of the front footpad is exactly on the transverse line at the end of the section, in which case the offset X is zero.
    6.  

    Figure 101. Illustration. Back end of front footpad is past the end of the test section when last reading is obtained. This figure shows the location of the front footpad at the end of the section for the case where the back end of the front footpad is past the end of the section. The distance to be measured is shown in the figure, which is the distance from the back end of the front footpad to the transverse line that is placed at the end of the section.
    Figure 101. Illustration. Back end of front footpad is past the end of the test section when last reading is obtained.

    Figure 102. Illustration. Back end of the front footpad is before the end of the test section when last reading is obtained. This figure shows the location of the front footpad at the end of the section for the case where the back end of the front footpad is located before the end of the section. The distance to be measured is shown in the figure, which is the distance from the back end of the front footpad to the transverse line that is placed at the end of the section.
    Figure 102. Illustration. Back end of the front footpad is before the end of the test section when last reading is obtained.

  8.  
  9. Repeat steps 3 and 4 two additional times.
  10.  

Computation of Dipstick® Footpad Spacing

  1. Compute the footpad spacing for the Dipstick® for each run using the following procedure:

    If back edge of front footpad was past the end of the section when the last reading was obtained (case shown in figure 101), use the following formula to compute footpad spacing:

    Footpad spacing (mm) = (30480 + X) /100    (3)

    Where:

    X is in mm.

    If back edge of front footpad was before the end of the test section when the last reading was obtained (case shown in figure 102), use the following formula to compute footpad spacing:

    Footpad spacing (mm) = (30480 - X) / 100    (4)

    Where:

    X is in mm.

    If the back edge of the front footpad is exactly in line with the end of the section, the footpad spacing is 304.8 mm.

    Compute the average footpad spacing for each Dipstick® by averaging the values obtained for the three runs (to two decimal places).

  2.  
  3. Maintain a log in the RSC office that indicate the following information: date when testing was performed, Dipstick® model number, diameter of the Dipstick® footpads, results from the field tests, computed footpad spacing for each run and the average footpad spacing. The suggested format of the log is shown in the following table (date of testing should be included in the log).

    Table 3. Suggested format of RSC office log.

    Dipstick ModelSerial NumberDiameter of Footpad
    (mm)
    Test Number Offset at End of Section(1)
    (mm)
    Footpad Spacing
    (mm)
    Average Footpad Spacing
    (mm)
    Front Back
        1   
        2   
        3   
        1   
        2   
        3   
        1   
        2   
        3   

    Note 1: Offset is positive if back end of front footpad is past end of section at last reading, offset is negative if back end of front footpad is before end of the section when last reading is obtained
  4.  
  5. Write the average Dipstick® footpad spacing and date when testing was performed on a sheet of paper and securely tape it to the inside of the Dipstick® carrying case.
  6.  

 

<< PreviousContentsNext >>

 


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).
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.
FHWA
United States Department of Transportation - Federal Highway Administration