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SCM Verification Testing

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Soil Compaction Meter Verification Testing
Summary Report (September, 2000)

Prepared By:
Robert Lee Cardenas
Foster-Miller, Inc.
350 Second Ave
Waltham, MA 02154
Prepared For and Sposored By:
Gas Research Institute
8600 West Bryn Mawr Ave
Chicago, IL 60631

GRI DISCLAIMER

LEGAL NOTICE: This report was prepared by Foster-Miller, Inc. (FMI) as an account of work sponsored by the Gas Research Institute (GRI). Neither GRI, members of GRI, nor any person acting on behalf of either:

  1. Makes any warranty or representation, express or implied, with respect to the accuracy, completeness, or usefulness of the information contained in this report, or that the use of any apparatus, method, or process disclosed in this report may not infringe privately owned rights; or
  2. Assumes any liability with respect to the use of, or for damages resulting from the use of any information, apparatus, method, or process disclosed in the report.

TEST PLAN

The test plan consisted of soil laboratory tests and bellhole backfilling tests. A test matrix for the bellhole test was defined to evaluate thirty-two combinations of five test factors. One test combination was evaluated in one bellhole test. Two repetitions of the test matrix were completed. The thirty-two test matrix was divided into matrix "A", matrix "B" and matrix "C". Matrix "A" was a sixteen test matrix in which all the test factors are evaluated following proper compaction guidelines. Matrix "B" was an eight test matrix in which the test factors are evaluated following compaction procedures that are outside the guideline recommendations. Matrix "C" was an eight test matrix that evaluated the performance of the SCM in conjunction with a vibratory plate compactor, rammer, jackhammer, or pneumatic pole tamper.

The laboratory soil tests determined the density curves for each of the four soils tested. Standard Proctor densities were used to evaluate the performance of the SCM. The acceptance criteria was a 0.95 ratio of the measured bellhole density to the Standard Proctor density.

For each test condition, a bellhole-sized excavation was backfilled and compacted in lifts. The SCM was used to monitor the compaction effort. Nuclear densitometer measurements for density and moisture were taken after completed passes. The first time through the test matrix, the measurements were taken prior to the SCM's stop compaction signal, immediately after the SCM's stop compaction signal and then for several passes after the SCM's stop signal. The second time through the test matrix, density readings were only taken immediately after the SCM's stop compaction signal. Density measurements were taken for each lift, with the exception of the first. No density measurements were taken on the first lift.

A logbook was kept and updated after each test and prior to the subsequent test. The logbook included the raw data sheets as well as a description of the test including date, time, operators, ambient conditions and observations. The data was also recorded in spreadsheet format compatible with Microsoft Excel.

FIELD TESTS

Testing was conducted at a sand and gravel pit local to the University of New Hampshire. Test soils were all available on site. Dr. Gress coordinated and supervised the effort.

Five factors were varied to define the thirty-two test conditions. The five factors and their levels include:

  1. Soil (SPSM, SP (bank run), CL, SP (sand))
  2. Moisture as determined by hand test ("soil ball method") and characterized as "DRY", "GOOD", "WET"
  3. Meter Setting (4, 6)
  4. Compaction Tool (Rammer, Jackhammer, Pneumatic Tamper, Vibratory Plate)
  5. Lift thickness (6" to 8", 9" to 12")

Soil and compaction tool had four levels. Moisture had three levels. Meter setting and lift thickness had two levels. Each of the thirty-two tests were repeated once to produce a total of sixty-four tests. Each test followed the sequence described below.

Test pits were excavated producing square holes which measured from four to seven feet on the sides and approximately four feet deep. The test pits were backfilled in lifts. Loose lift thickness varied as defined by the test matrix. The backfilling procedure was:

  1. A base lift was placed in the pit and compacted with two passes;
  2. A sensor was placed at approximately the center of the bottom surface of the pit;
  3. A second soil lift was placed into the pit and leveled;
  4. Each lift was compacted in a series of uniform passes, until the stop compaction light came on indicating optimum compaction had been achieved;
  5. The soil density was measured; and,
  6. Steps 3 through 5 were repeated until the test pit was filled.

Steps 4 and 5 were varied in thirty-two of the sixty-four tests. In those thirty-two tests, density measurements were taken three or four times per lift. These measurements were taken after the first pass, after the stop compaction signal, after the stop signal plus two additional passes, and after the stop signal plus four additional passes.

In order for the SCM to set the gain properly, the compaction pattern had to pass directly over the sensor within two seconds of starting the compactor. Therefore, the compaction process always started over the sensor and then moved to the perimeter of the test pit. Thereafter, the compaction pattern simply provided uniform coverage of the lift.

Sand cone density tests were randomly taken throughout the test program as a check for the nuclear densitometer.

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