MBW Inc.
Compaction & Concrete Construction Equipment

SCM Verification Testing: Page 2

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SOILS

Four soils were used throughout the program. Three of the soils were available from stockpiles and excavations at a local sand and gravel pit. The fourth soil was produced by blending two of the available three soils. Using the Unified Soil Classification system, the soils are classified:

1. CL, silty clay
2. SP, poorly graded sand
3. SP, poorly graded sand
4. SWSM, well graded silty sand

The intent was to use a range of soils that would be representative of soils used in backfilling operations. With the exception of the clay, all of the soils would be considered acceptable backfilling material. The SP soils were an indication of how varied soils can be even within a given soil classification. One of the SP soils was a fairly clean, uniform sand. The second SP soil had a higher percentage of coarse material. This slight difference in material made a significant difference in Proctor values. Blending a SP soil with a coarser SM soil in an effort to achieve a SPSM soil produced the SWSM soil. The blend just missed meeting the SPSM classification resulting in a well-graded material.

Table 1 lists the technician's field identification, the unified soil classification, the standard proctor values and the modified proctor values for the four test soils. Two of the soils have corrected and uncorrected proctor values. Modified proctor tests were included at the request of MBW, however, were not used in the SCM's evaluation.

TEST DATA

A total of sixty-four test pits were excavated and backfilled, resulting in two hundred ninety-four lifts being compacted and over one thousand individual density readings. All of the data is organized by test number. Each test is associated with three data sheets. The first is a summary sheet of the test conditions and lifts. The second sheet is a summary of average moisture and proctor values. The third data sheet lists all the density data recorded for the test. These sheets are a compilation of all raw data used in the test analysis. Sample data sheets are illustrated in Figures 1, 2, and 3.

Figure 1 illustrates the first data sheet. All the general information about the test, test conditions, SCM, compaction tool, soil ball condition and Proctor Density values is included on this sheet. Figure 1 also has data on the number of lifts, lift heights, number of passes, and the total time to complete the passes. For example, Figure 1 illustrates test 7 tested conditions defined by matrix A1. Figure 1 also shows that a 7" floor lift was compacted in 2 passes. Then four lifts were compacted to fill the excavation. The "Red Light" came on during the first pass on layers three and four. Layers one and two required two passes before the "Red Light" came on. Test 7 collected data for diminishing returns verification, hence density data was collected on the first pass, the "Red Light" pass, the "Red Light" pass + 2 passes and the "Red Light" pass + 4 passes. The times recorded are for the total time to complete the number of passes. For example, lift 2 achieved a "Red Light" condition in two passes with the red light coming on in 2 minutes and 43 seconds and the lift completed in a total time of 3 minutes and 7 seconds.

Figure 2 illustrates the second data sheet for test seven. This sheet summarizes the average density and moisture for each density test. The coefficient of variation (standard deviation divided by average) is also given for each data entry. The data sheet also lists density for a given lift as a percentage of the "Red Light" density. This data is used to verify that the "Red Light" condition occurs at a point of diminishing returns on density. The other data present on the sheet are the "Red Light" density as a percentage of Proctor density. This data is used throughout the data analysis. Finally, statistics on the moisture content of the test are provided.

Figure 3 illustrates the last data sheet for test seven. All the raw density and moisture readings are recorded on the sheet. Also recorded are the statistics for each set of density measurements. Each lift has four test positions listed. Each test position has four samples. The lift designation is for the lift being tested. The position is an indication of location on the lift surface where the sample was taken. For any given lift, test locations did not repeat in any one position. The samples are the individual one-minute nuclear densitometer readings taken at each position. As indicated on the test 7 data sheet, four individual readings were taken at each position. For each of these readings, the densitometer was rotated ninety degrees about the meter probe. Later in the test program only three readings were taken at one-hundred-twenty degree intervals. If the "Red Light" came on during the first pass, then only three positions are recorded. The statistics are based on the set of three or four test readings as the case may be. For each individual reading, a nuclear densitometer will produce a reading that is plus or minus 0.2% in density and plus or minus 2% in moisture. The statistics in the data table are for the set of individual readings; hence, the variation is much larger than indicated for the densitometer.

Figure 4 illustrates the summary density data as it relates to the test matrices. Once again using test 7 as an example, the density data presented as percent Proctor density is listed for each "Red Light" condition for the test. These data sheets are organized to evaluate and compare factors within soil groups. On this data sheet, the data has been corrected to account for errors in lift thickness. For example, in test 9 the first lift was out of specification of the A1R (matrix A1 repeat) for the loose lift height. The density data is marked with Italics and not used as part of the A1R data. Instead, it is included in the A2R data where it does meet the lift height specification. If the data point did not fit in another category, then it was left out of lift height comparisons. However, it would have been included in other comparisons where appropriate. These data sheets also include one-sided T tests for determining the confidence level of achieving 95% Standard Proctor Density.

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