MBW Inc.
Compaction & Concrete Construction Equipment

SCM Verification Testing: Page 3

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DATA ANALYSIS (Red Light Density)

The first objective of the test program was to verify that the SCM did signal a "Red Light" condition at a point of diminishing returns for the soil density. To accomplish this, additional density measurements were taken on thirty-two of the sixty-four test excavations. Density measurements were recorded after the first pass, after the "Red Light" pass, then after 2 additional passes and again after 4 additional passes. Under normal operating conditions, lift compaction would have stopped at the "Red Light" pass. All the densities were normalized to the "Red Light" density in order to directly compare the different soils. These normalized values were summarized in data sheet "Summary of Red Light Density Data". Table 2 provides a summary of that data sheet.

A review of the average values and the upper and lower of the 95% confidence interval illustrate that the density varies at most by two percent with four additional passes. This also illustrated graphically in Figure 5. Both Table 2 and Figure 5 also illustrate the maximum and minimum values of the density data for each pass category. The very low values were recorded in clay test pits (1998 tests). As discussed previously, the 1998 clay tests were conducted with very wet material, which was most likely a factor in the resulting low values. This same data was not collected in the 1999 clay tests. Table 2 and Figure 5 include data from all of the test conditions evaluated. The results are therefore representative of the backfill and compaction operations.

The test results clearly support the claim that the meter will signal for stopping compaction when the density is very close to the maximum value. Additional compaction results in only a minor increase (less than 2%) in soil density.

COMPARISON TO STANDARD PROCTOR DENSITY

The second verification objective was to test for at least 95% Standard Proctor Density at the SCM’s stop compaction (Red Light) signal when conditions of moisture, lift depth, and compaction equipment were characterized as adequate or good. An analysis of densities measured after the "Red Light" did verify this premise on 3 of the 4 soils tested. The fourth soil (CL) did not represent a failure of the SCM to signal at 95% under adequate conditions as all lifts tested were determined to be overly wet relative to optimum.

All "Red Light" densities are summarized as percent of Standard Proctor Density and listed by soil and test matrix in eight data tables ("Summary of Percent Proctor Results"). A one-sided T-test was used to evaluate the data and determine if the achieved densities met the 95% Standard Proctor Density at the 95% confidence level. From this data, the lower limit of the 95% confidence interval for each test condition was determined. This data summary is presented in Table 3, Table 4, Table 5, and Table 6. Tables 3 through 6 are separated by soil types and list the test Matrix ID, the actual test conditions, the measured moisture content, the density ratio (measured density: Standard Proctor Density) uncorrected, corrected, and sample size. The density ratio is reported as the average and the lower limit of the confidence interval. The density results are reported for each Matrix ID and for the total matrix group. Table 6 includes data from both the 1998 clay testing and the 1999 clay testing.

All field densities were measured using a nuclear densitometer. These measurements were spot-checked using the Sand Cone Method of field density measurements. This data is provided in Attachment 3 "Summary of Sand Cone Density Data". The data shows that there was no statistical difference between the Sand Cone densities and the Nuclear densities. Summarized on the same data sheet is an analysis of the Coefficient of Variation (average/standard deviation) which was, for all the nuclear readings, 1.77% plus or minus 0.09%. From these results, we conclude that the nuclear data was a good indication of the measured density.

Corrected or Uncorrected Standard Proctor values…which value to use? Standard Proctor Tests allow for adjusting measured density values to account for rock content in the test sample. The correction is empirical. Discussions with PSI, Inc. (the soil-testing firm used during this test program) indicated that using corrected values can lead to Proctor densities that can not be achieved in the field. Further, PSI pointed out that the American Association of State Highway Officials (AASHO) does not require corrections for rock content. Both corrected and uncorrected values are provided in this test report, but objective verification has been based on uncorrected data.

SWSM (Blend)

Table 3 summarizes the results of the SWSM data. The data illustrates that for uncorrected Proctor densities, the 95% criteria was met under all test conditions at the 95% confidence level. This is illustrated by comparing the uncorrected lower limit value to 95. As can be seen all values exceed the 95. Test Matrix ID C1, C2 and B1 through B4 all defined test conditions that were not considered favorable for good compaction. The ID numbers had moisture conditions that were characterized as "DRY" or "WET" and in some cases loose lift heights that were 9 to 12 inches. Under these conditions the probability of meeting the Standard Criteria is not as high as it is for conditions that are adequate for good compaction. Matrix ID C3, C4 and A5 through A8 characterized good compaction conditions. The table illustrates that densities for soil conditions characterized as "Good" are greater than other densities associated with other characterizations. The lone exception is test A7 using the Jackhammer.

The corrected data produces a different result but still consistent with proper SCM performance. For the test conditions that were not good for compaction, the 95% criteria was not met. For the test conditions that were good for compaction, the 95% was met with the exception of test A7. Again, test A7 used the Jackhammer with a compaction foot.

Jackhammer compaction operation differs from the other compactors tested. Due to the weight of the tool, Jackhammer compaction is usually a step by step process. One spot is compacted then the next adjacent spot is compacted until the lift surface is completed. Vibratory plates, rammers and pneumatic tampers sweep over the lift surface in a continuous pattern that has the compactor constantly moving. The SCM’s gain setting algorithm is designed to recognize a compactor sweeping the lift surface and achieving density progressively in passes. As a result, the SCM frequently signaled the "Red Light" condition before the entire surface had been compacted with a spot compacting Jackhammer. When this happens, the guideline procedures stipulate that the lift be completed in a consistent and uniform manner. From a practical viewpoint, Jackhammer results were excellent when checked with a densitometer and readings consistent with other compaction tools.

The optimum moisture content of the SWSM soil was 10.2% (see Table 1). All of the measured moistures are dry of optimum. This soil was free draining and the soil moisture was measured after compaction, and therefore, several minutes after the soil ball test was completed. The moisture measurement for the "DRY" condition is probably an accurate indication of the soil ball test moisture. The "GOOD" and "WET" conditions may have had moisture contents slightly higher than measured only because the water would have had a chance to partially drain from the fill. "DRY" soil conditions ranged from 4 to 4.8%, "GOOD" soil conditions ranged from 6 to 7.1% and "WET" conditions ranged from 7.1 to 7.7 percent, again, all dry of optimum.

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