Full-Scale Testing

Overload Update

REDAC Subcommittee on Airports

David R. Brill, P.E., Ph.D.

August 25, 2015

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Federal Aviation

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Federal Aviation

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CC7 Overload Test Objectives

Develop rational overload criteria for flexible pavements.

Consider criteria in terms of:

Percent by which the ACN of the overloading gear exceeds the reported PCN of the pavement.

Used pavement life expressed as cumulative damage factor (CDF).

Effect of overload gear configuration (D, 2D, 3D).

Compare the results to current ICAO standards published in Annex 14.

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August 25, 2015

Full-Scale Testing - Overload Update

Federal Aviation

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Current ICAO Overload Criteria

ICAO Annex 14, “Aerodrome Design and Operations,” defines the following overload criteria:

for flexible pavements, occasional movements by aircraft with ACN not exceeding 10 per cent above the reported PCN should not adversely affect the pavement;

for rigid or composite pavements, in which a rigid pavement layer provides a primary element of the structure, occasional movements by aircraft with ACN not exceeding 5 per cent above the reported PCN should not adversely affect the pavement;

the annual number of overload movements should not exceed approximately 5 per cent of the total annual aircraft movements.

In addition, overloads should not be allowed on pavements exhibiting distress or failure, or during periods of thaw.

The airport authority should review the pavement condition regularly, and review overload criteria periodically.

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August 25, 2015

Full-Scale Testing - Overload Update

Federal Aviation

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CC7 Test Item Layout

August 25, 2015

Full-Scale Testing - Overload Update

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Federal Aviation

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CC7 Overload Test Items

40-ft. (12.2-m) test items separated by 10-ft. (3 m) transitions.

CBR 5 (subgrade category C)

All 6 test items have the same structure.

Thin HMA sections represent GA airports receiving occasional overload operations.

3 in. P-401

6 in. P-209

P-154 thickness designed to give nominal PCN = 35/F/C. 

Assumed “lifetime” traffic of 27,000 passes of NAPTF 72,000-lb. dual gear (36,000 lbs. per wheel).

Use COMFAA 3.0 to compute PCN.

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August 25, 2015

Full-Scale Testing - Overload Update

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Instrumentation Layout (LFC1-S)

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TSG – Transverse Strain Gage

LSG – Longitudinal Strain Gage

MDD – Multi-Depth Deflectometer

PC – Pressure Cell

MS – Moisture Sensor

SS – Suction Sensor

T – Thermocouple 

August 25, 2015

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General Test Procedures

ACN-Based Overload Test Items:

Traffic at “normal” load (D-36) until rate of rut depth accumulation (RRDA) stabilizes*.

Increase load to 110% PCN. Traffic until RRDA stabilizes, but not more than 1350 passes (5% lifetime traffic).

Resume traffic at normal load. Observe any change in RRDA or other responses (MDD, strain).

Increase load to 120% PCN and traffic until RRDA stabilizes.

Repeat steps 3 & 4 following the overload schedule. Continue until failure is observed.

* “Stable” is defined as an approximately constant rate of total rut depth accumulation with applied passes, following any initial shakedown phase.

CDF-Based Overload Test Items:

Traffic at “normal” load (D-36) until rate of rut depth accumulation (RRDA) stabilizes*.

Apply one wander pattern at overload designed to consume CDF = 0.1.

Resume traffic at normal load. Observe any change in RRDA or other responses (MDD, strain).

Apply one wander pattern at overload designed to consume CDF =0.25.

Resume traffic at normal load. Observe any change in RRDA or other responses (MDD, strain).

Apply one wander pattern at overload designed to consume CDF =0.5.

Resume traffic at normal load. Observe any change in RRDA or other responses (MDD, strain).

Apply one wander pattern at overload designed to consume CDF =1.0.

If Step 6 does not fail the test item, return to normal load(dual) and traffic until the pavement behavior stabilizes or failure is observed.

Repeat Steps 8 and 9 until failure.

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August 25, 2015

Full-Scale Testing - Overload Update

Federal Aviation

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Overload Schedules
| ACN Criterion |          |       |        |                   |
|---------------|----------|-------|--------|-------------------|
| Gear Type     | Overload | ACN   | Passes | Wheel Load, lbs.1 |
| D             | 100% PCN | 35.02 | N/A    | 36,000            |
| D            | 110% PCN | 38.38 | N/A    | 39,000            |
| D            | 119% PCN | 41.82 | N/A    | 42,000            |
| D            | 126% PCN | 44.14 | N/A    | 44,000            |
| D             | 146% PCN | 51.26 | N/A    | 50,000            |
| D             | 164% PCN | 57.56 | N/A    | 55,000            |
| 2D           | 110% PCN | 38.63 | N/A    | 35,500            |
| 2D           | 121% PCN | 42.44 | N/A    | 38,000            |
| 2D           | 130% PCN | 45.65 | N/A    | 40,000            |
| 2D            | 149% PCN | 52.31 | N/A    | 44,000            |
| 2D            | 175% PCN | 61.30 | N/A    | 49,000            |
| 3D           | 111% PCN | 38.71 | N/A    | 34,500            |
| 3D           | 120% PCN | 42.06 | N/A    | 36,500            |
| 3D           | 130% PCN | 45.56 | N/A    | 38,500            |
| 3D            | 148% PCN | 51.91 | N/A    | 42,000            |
| 3D            | 171% PCN | 59.76 | N/A    | 46,000            |
| CDF Criterion |            |     |               |                   |
|---------------|------------|-----|---------------|-------------------|
| Gear Type     | Overload   | ACN | Passes        | Wheel Load, lbs.2 |
| D            | CDF = 0.09 | N/A | 66 (1 wander) | 46,000            |
| D            | CDF = 0.25 | N/A | 66 (1 wander) | 52,000            |
| D            | CDF = 0.49 | N/A | 66 (1 wander) | 57,000            |
| D             | CDF = 0.98 | N/A | 66 (1 wander) | 62,500            |
| 2D           | CDF = 0.10 | N/A | 66 (1 wander) | 40,500            |
| 2D           | CDF = 0.25 | N/A | 66 (1 wander) | 45,500            |
| 2D           | CDF = 0.51 | N/A | 66 (1 wander) | 50,000            |
| 2D            | CDF = 0.98 | N/A | 66 (1 wander) | 54,500            |
| 3D           | CDF = 0.10 | N/A | 66 (1 wander) | 37,000            |
| 3D           | CDF = 0.25 | N/A | 66 (1 wander) | 41,500            |
| 3D           | CDF = 0.51 | N/A | 66 (1 wander) | 45,500            |
| 3D            | CDF = 1.06 | N/A | 66 (1 wander) | 50,000            |

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ACN-Based Overload Test Items LFC S-1, 2, 3

CDF-Based Overload Test Items LFC S-3, 4, 5

1Based on COMFAA 3.0

2Based on FAARFIELD 1.4

Wheel loads are adjusted to the nearest 500 lbs. due to vehicle limitations.

August 25, 2015

Full-Scale Testing - Overload Update

 Indicates that overload has been completed.

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CC7 Overload Test Summary

August 25, 2015

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| Test Phase | Dates                      | Vehicle   |         | Test Items  LFC1-S – LFC3-S   | Test Items  LFC4-S – LFC6-S   | Description                     |
|------------|----------------------------|-----------|---------|-------------------------------|-------------------------------|---------------------------------|
|            |                            | Passes    | Wanders | Passes                        | Passes                        |                                 |
| 1          | 10/6/14 –      10/16/14    | 1-924     | 1-14    | 1-924                         | 1-924                         | Initial normal load             |
| 2          | 10/20/14                   | 924-990   | 15      | -                             | 925-990                       | 0.1 CDF Overload                |
|            | 10/21/14 –      10/28/14   | 991-1650  | 16-25   | 925-1584                      | -                             | 10% ACN Overload                |
| 3          | 10/29/14 –      11/13/14   | 1650-3168 | 26-48   | 1585-3102                     | 991-2508                      | Resume Normal Load              |
| 4          | 11/17/14                   | 3169-3234 | 49      | -                             | 2509-2574                     | 0.25 CDF Overload               |
|            | 11/17/14 –      11/25/14   | 3235-4224 | 50-64   | 3103-4092                     | -                             | 20% ACN Overload                |
| 5          | 12/2/14 –      12/4/14     | 4225-4752 | 65-72   | 4092-4620                     | 2574-3102                     | Resume Normal Load              |
|            | 12/4/14                    |           |         |                               |                               | Test suspended  until June 2015 |
| 6          | 6/15/15 –      6/22/15     | 4753-5544 | 73-84   | 4621-5412                     | 3103-3894                     | Resume Normal Load              |
| 7          | 6/29/15                    | 5545-5610 | 85      | -                             | 3895-3960                     | 0.50 CDF Overload               |
|            | 6/29/15 –     7/6/15       | 5611-6468 | 86-98   | 5413-6270                     | -                             | 30% ACN Overload                |
| 8          | 7/8/15 –     8/10/15       | 6468-8778 | 99-133  | 6271-8580                     | 3961-6270                     | Resume Normal Load              |
| Total      |                            | 8778      | 133     | 8580                          | 6270                          |                                 |

As of August 10, 2015

Federal Aviation

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Rut Depth Monitoring

Physical 16-foot straight edge.

Rail-to-rail profile data.

Generates raw data files at 2.5 mm from Selcom laser.

Decimate to 25 mm.

Compute a virtual 16-ft. straight edge rut depth.

360° Ultra-High-Speed Laser Scanner (Leica Model P20)

New source of highly accurate profile data.

Use scans to correct rail-to-rail profiles for beam curvature.

Extracting transverse profiles from acquired scans is a time consuming process. We are working to improve efficiency.

Profile data are collected:

After every completed wander pattern (66 passes).

At intermediate passes on the zero track (24 and 48 passes) during overload or if deemed necessary.

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August 25, 2015

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Rut Depth Monitoring

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Rail-to-Rail Profiler

16-ft Straight Edge

August 25, 2015

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Ultra-high Speed Laser Scanner

 Leica ScanStation P20

Scan of the Reflective Testing Rig

August 25, 2015

Full-Scale Testing - Overload Update

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Federal Aviation

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Average Rut Depth – LFC-1

August 25, 2015

Full-Scale Testing - Overload Update

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2-Wheel Gear Overload

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Average Rut Depth – LFC-2

August 25, 2015

Full-Scale Testing - Overload Update

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4-Wheel Gear Overload

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Average Rut Depth – LFC-3

August 25, 2015

Full-Scale Testing - Overload Update

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6-Wheel Gear Overload

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Rate of Surface Rutting – LFC-4

August 25, 2015

Full-Scale Testing - Overload Update

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6-Wheel Gear Overload

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Rate of Surface Rutting – LFC-5

August 25, 2015

Full-Scale Testing - Overload Update

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4-Wheel Gear Overload

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Rate of Surface Rutting – LFC-6

August 25, 2015

Full-Scale Testing - Overload Update

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2-Wheel Gear Overload

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MDD Rutting Measurement

August 25, 2015

Full-Scale Testing - Overload Update

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A-C = Rut in P-154D-F = Rut in P-152 (Subgrade)F = Total from surface

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MDD Rut Accumulation (MDD-11)

August 25, 2015

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Federal Aviation

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Preliminary Observations

Observed an increase in the rate of rutting after overload of 0.5 CDF and 130% of PCN. 

Number of wheels in overload gear does not appear to have a significant effect on permanent damage for the same ACN or CDF.

MDDs show rutting accumulates primarily in the P-154 subbase layer.

We will continue to traffic all test items to failure.

August 25, 2015

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Federal Aviation

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