CC5 Profiler and Rut Depths

 

Pavement permanent deformation (rutting) was monitored by performing transverse profile measurements.  The figure below depicts the test plan for profile measurements with the test items shown.  Profile measurements were performed concurrent with trafficking of the test items.  According to the test plan, transverse profiles were collected along 3 lines in each test item for a total of 18 lines for the entire experiment.  The figure below depicts the transverse lines where the profiles were collected.  The transverse profiles on the middle line of each test item, shown as either line 2 or 5, were analyzed to calculate the rut depth for the test item.  The figure also includes the years in which the test items were tested.

Search the CC5 Profile Database.


Transverse Profile Data Collection Plan.


Transverse Profilers

Over the course of CC5 testing, the FAA implemented 3 different profilers.  Transverse profiles were initially measured using an FAA profiler that was 21 feet long.  This profiler was only used on the north test items and was retired on September 9, 2008 after 4,686 passes were made.  The shortcoming of this profiler was that it was not of sufficient length to capture the entire 30-foot width of the pavement with one measurement. 

After September 9, 2008 a new profiler was put into service that was 30 feet long.  This profiler was used to take the measurements starting with pass 5,016.  This profiler continued to be utilized in 2009 and 2010 as well.

Both the 21 and 30 foot profilers operated by moving an infrared laser to measure the vertical displacement, and an incremental rotary encoder was used as a DMI on a trolley rolling along the steel flange of an aluminum truss type beam.  A pavement profile consists of DMI measurements from the edge of the pavement paired with the vertical displacement measurements from the transducer.  The supporting points of the transverse profiler were placed on the pavement surface.  As such, the vertical reference points for transverse profiles were a function of the pavement surface condition.  A signal acquisition box was assembled onto the profiler to collect and store the profile data. 

 

30-Foot Profiler

 

In 2012, a new transverse profiler (the Rail to Rail Profiler) was adopted by the FAA.  The new profiler was 66 feet long and captured the entire width of both south and north test items in every run.  The profiler was installed on a truss that ran on the rail system used for the NAPTF test vehicle.  The rail is made of steel and the truss structure is made of aluminum.  The supporting points of the transverse profiler were located on the rail, which allowed maintaining the same vertical reference points for all the transverse profiles.  The profile measurements were not impacted by the surface condition such as depression and upheavals because of using the fixed end points not on the pavement surface.

Rail to Rail Profiler

 

This profiler operated the same as the 21 and 30 foot profilers.  Different coefficients of thermal expansion between the steel and aluminum at the top and bottom of the profiler can impact the curvature of the profiler.  Depending on the ambient temperature, this can lead to an increase or decrease to the sagging shape of the profiler as shown in the figure below.  A stable concrete surface at Station 300 in the NAPTF outside of the test area was designated as the reference line.  The referenced line was surveyed to provide an accurate surface to use as a datum and a profile of the reference line was taken prior to each profile measurement.  The reference profiles allow the measured profile to be adjusted for the beam curvature induced by temperature. 


Figure of Temperature Induced Profiler Beam Curvature


Transverse Profile Data

Transverse profiles were taken on each test item of CC5.  In the CC5 Transverse Profile Analysis Report, there is an in-depth discussion of the type, date, location of each profile, naming conventions used and complete profile data information.

Search the CC5 Profile Database.

Rut Depth Analysis

Two methods were used for the experiment to calculate the rut depth: baseline method and straightedge method. The baseline method calculates the rut depth with respect to the profile that was measured at the beginning of the testing. The straightedge method calculates the rut by implementing an imaginary straightedge placed upon the upheavals. The following test items explain more details of the methods implemented for the analysis.

Baseline Method

In this method, surface rut is measured from a fixed baseline profile. The pavement profiles before trafficking are used as baseline profiles, and the rut depth for any subsequent profile measurement is calculated as the maximum difference between the measured profile and the baseline. The figure below illustrates the calculation of rut depth using the baseline method.


Maximum Rut Depth Calculation Using Baseline Method.

The baseline method is inherently based on the comparison of the profiles as the testing progresses.  Processing of the profile data was necessary to address the different length profilers with respect to the rutting of the test items being measured.  For further explanation please reference the CC5 Profile Analysis Report.

Straightedge Method

In the straightedge method, the maximum deflection between the profile and an imaginary straightedge that connects the upheavals is measured as the rut depth, as shown in the figure below. With this method, the calculation of rut depth for each profile is independent of a baseline profile and the impact of upheavals is also accounted for in the calculation of rut depth. This could be viewed as an advantage over the baseline method since the baseline method is indifferent to the creation and elevation of the upheavals. This is particularly important in test items where upheavals grew higher than other test items.

Maximum Rut Depth Calculation Using Straightedge Method.

 

Rut Depth Analysis Findings

The figures below compare the accumulation of rut depth over the testing period for all the CC5 north and south test items utilizing the baseline and straightedge methods.  A direct comparison between the rut depths of all test items is not possible, as each test item was constructed with different pavement structures and were trafficked with different gear configurations and different load levels. The comparisons that follow were made on relevant test items.

Accumulation of Surface Rut on North Test Items Using Baseline Method.

 

 

Accumulation of Surface Rut on North Test Items Using Straightedge Method.

 

 

Accumulation of Surface Rutting on South Test Items Using Baseline Method.

 

 

Accumulation of Surface Rutting on South Test Items Using Straightedge Method.

 

 

For a more in-depth analysis of the rutting process, please see the CC5 Transverse Profile Analysis Report. To view the Rut Depth Summary for both the north and south sides, see the following:

CC5 North Rut Depth Baseline (PDF)

CC5 North Rut Depth Straightedge (PDF)

CC5 South Rut Depth Baseline (PDF)

CC5 South Rut Depth Straightedge (PDF)

 

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