New Jersey

Department of Transportation

Standard Specifications

for Road and Bridge Construction


NJDOT B-1 Falling Head Permeability Test for Asphalt-Stabilized
Drainage Course

  1. Scope. This test method is used to determine the permeability of Asphalt-Stabilized Drainage Course (ASDC) materials.

  2. Apparatus. Use the following apparatus:

    1. Falling head permeability apparatus consisting of the following:

      1. A 4-inch inside diameter standpipe that is at least 25 inches high with 2 timing marks approximately 16 inches apart
      2. A top support that will fit over the mold and into which the standpipe will fit with a clamping system to ensure that it will not leak during testing.
      3. A bottom support into which the mold can fit and capable of supporting the apparatus with a clamping system to ensure that it will not leak during testing. Include a flap gate in the bottom of the bottom support to keep the water from flowing until after the testing has begun.
      4. Two rubber gaskets.

    2. Steel cylinder molds 8-inch high 4-inch inside diameter.
    3. A steel ruler with 0.01-inch graduations.
    4. A stopwatch capable of measuring up to 30 minutes with an accuracy of 0.1 second.
    5. A source of clean cold tap water.

  3. Procedure. Perform the following steps:

    1. Prepare and compact 3 ASDC specimens according to AASHTO T 167.
    2. Measure the height of the mold, the distance from the top of the mold to the top of the compacted specimen, and the distance from the bottom of the mold to the bottom of the compacted specimen. Calculate the compacted height of the ASDC sample (L) in inches as the height of the mold minus the 2 distances measured.
    3. Place a 4-inch diameter cylinder mold with a compacted ASDC specimen into the bottom support ring of the falling head permeability apparatus. Place a rubber gasket along the bottom edge of the cylinder mold to prevent water leakage.
    4. Place a rubber gasket at the top edge of the cylinder mold.
    5. Place the upper support ring and plastic standpipe on top of the 4-inch diameter cylinder mold.
    6. Lock the upper support ring to the cylinder mold with the wing nuts. The permeability apparatus is now assembled and ready for permeability testing.
    7. Place the assembled permeability apparatus near the water source and a suitable drain.
    8. With the bottom flap gate closed, fill the plastic standpipe to the top with water and then turn off the water.
    9. Start the permeability flow test by opening the bottom flap gate to allow water to flow through the specimen.
    10. Start the stopwatch when the water level drops to the first timing mark down from top of the standpipe.
    11. Stop the stopwatch when the water level drops to the second timing mark down from the top of the standpipe.
    12. Record the time in seconds.
    13. Repeat the permeability test with additional compacted ASDC specimens for a total of 3 trials.

  4. Calculations. Calculate the permeability of each sample using the following equation:

      K = Falling head permeability (feet/day).
      L = Height of compacted ASDC specimen.
      T = Time in seconds for water level to fall from first timing mark to second timing mark.
      h1 = Distance in inches from first timing mark to bottom of specimen.
      h2 = Distance in inches from second timing mark to bottom of specimen.
      ln = Natural logarithm.

  6. Report. For each of the 3 compacted ASDC samples, report L, T, h1, h2 and the permeability. Report the average permeability of the 3 samples.

Last Document Correction:
December 14, 2007