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SP (BANK RUN)
The bank run SP soil had a high enough rock content to allow for rock corrections to the Standard Proctor Density. Test results for this soil are summarized in Table 4. This soil was tested under eight conditions. Two of the eight (Matrix ID C5 and C6) were not right for good compaction due to dry soil conditions. All other conditions were right for good compaction. For this soil the 95% Standard Proctor criteria were met for all tests, both uncorrected and corrected values. The "DRY" soil conditions produced the lowest densities. It is interesting to note that, in this soil, the jackhammer produced the highest density.
The optimum moisture content of the SP bank run soil was 14.4% (see Table 1). All of the measured moistures were 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 2.2 to 2.4%, and "GOOD" soil conditions ranged from 3.8 to 6.1%, all dry of optimum.
SP (SAND)
The sand SP soil was clean uniform sand and did not require a rock correction for the Proctor value. This soil is typically easily compacted and was only tested under conditions adequate for good compaction. Table 5 confirms this with all results in excess of 100% Standard Proctor Density.
The optimum moisture content of the SP sand soil was 14.4% (see Table 1). The "GOOD" soil condition had a moisture content range from 6.2 to 8.3. Again this was a free draining soil and the actual soil ball moisture content may have been higher.
CL (CLAYEY SILT)
Two series of tests were completed using clay soil. The first tests were conducted in 1998 as part of the verification test matrix. The result of these first tests was that none of the tests met the 95% Standard Proctor acceptance criteria. As is discussed in the 1998 CL Tests section, analysis of the test data demonstrated that all the soil moistures were too wet for adequate compaction. In short, all tests were conducted with "Wet" moisture conditions and were therefore not conducive to adequate soil compaction. This was caused by a misleading soil ball test (see the Soil Ball Test for Clay section). It should be noted that although the Standard Proctor Density was not met, the soil was compacted to its maximum achievable density given the soil conditions. This is exactly what the Soil Compaction Meter helps the operator to achieve. Using the meter in conjunction with proper soil conditions yields the densities that meet the Standard Proctor Density criteria (see the 1999 CL Tests section).
A second test program was undertaken in 1999 to evaluate the part of the original test matrix that called for clay soil with "Dry" and with "Good" soil moisture conditions. For these tests, the in-situ soil moisture was greater than optimum moisture. The soil was dried to just dry of optimum for the "Good" moisture content and to very dry of optimum for the "Dry" moisture content. Controlling the moisture content resulting in soil densities that met the 95% Standard Proctor Density criteria for the "Good" moisture conditions and for the "Dry" moisture conditions when compacted with a pneumatic tamper. The "Dry" moisture condition did not produce a density that met the Proctor Density criteria when compacted with a jackhammer.
Clay soils are difficult to compact and require close attention to maintaining good compaction conditions for achieving adequate compaction. The two series of clay tests best illustrate the function of the soil compaction meter. Under "Wet" conditions, using the meter prompted continued compaction effort until the maximum achievable density for the given conditions was reached albeit less than the accepted density criteria. Under "Dry" conditions, the pneumatic compactor produced enough compaction effort to achieve soil densities that met the Proctor Density criteria. The jackhammer did not produce enough compaction effort to achieve the density criteria even with a shallow lift. Under "Good" moisture conditions, the jackhammer and the other compactors produced densities in excess of 95% Standard Proctor Density with a 95% confidence level.
The second series of tests were used to redefine the soil ball tests for Clay soils. This is discussed in the Soil Ball Test for Clay section.
1998 CL TESTS
The CL soil did not achieve 95% Standard Proctor Density over any of the test conditions. The clay was tested under favorable and unfavorable conditions for compaction. Clay is not considered a suitable material and is very difficult to compact, especially if wet. The optimum moisture for this material was 18.1% (see Table 1). Table 6 (1998 tests) illustrates that all moisture conditions were wet of optimum moisture. In Table 6, the soil ball moisture column indicates the actual moisture condition and in parenthesis the planned moisture condition. Although the moisture levels were graded using the soil ball tests, the moisture was too high to achieve the 95% Standard Proctor Density criteria.
For a given soil and moisture content, there is a maximum density value that can be achieved. This density occurs when the soil is completely saturated (S=100%). Figure 6 is a moisture density plot for the CL material. The figure plots the dry density of the CL material as a Percent of Standard Proctor Density against the Percent Moisture content. The three lines on the plot represent saturation levels of 100%, 90% and 80%. Also illustrated on the plot are the Standard Proctor Density and the Modified Proctor Density. Both the Standard Proctor Density and Modified Proctor Density represent maximum dry densities for a given compactive effort. For a given soil, the maximum densities for different compactive efforts are achieved at about the same saturation point. For the CL soil in Figure 6, the maximum density is achieved between eighty and ninety percent saturation. Figure 6 illustrates that all of the test moistures approached these saturation levels. Given that the saturation lines define lines of maximum density, the CL soil was compacted to a maximum density given the moisture conditions. However, that maximum density was below the 95% Standard Proctor Criteria. Although the density acceptance criterion was not achieved, the clay tests demonstrate that, using the meter and the compaction procedures, results in optimum density for the given compaction condition.
All the clay tests completed in 1998 are included in the data where "Wet" soil conditions are indicated.
1999 CL TESTS
Six tests were redone to meet the moisture requirements defined in the test matrix. These included Matrix ID numbers A9, A10, A11, A12, B5 and B6. The results are summarized in Table 6 (1999 tests) and are identified as "Redo" tests. Table 6 (1999 tests) also categorizes all the clay tests according to the redefined soil ball moisture test resulting in all the 1998 tests has being too wet for compaction. The soil for tests B5 (redo) and B6 (redo) was dried to 15.5% moisture content (optimum was 22.7%). At 15.5%, a soil ball could not be formed. For tests A9 (redo), A10 (redo), A11 (redo) and A12 (redo) the soil was dried to 19.9% and formed a firm ball that broke up into large clumps.
Figure 7 illustrates the moisture density plots for the soil used during the 1999 tests. For this soil, the optimum moisture was higher than the soil used in the 1998 tests and the proctor density was slightly lower.
Table 6 shows that under good moisture conditions the 95% Standard Proctor Density Value is achieved at a 95% confidence level. Test A10 is slightly under at the lower confidence limit with 94% of Standard Proctor Density. For the redo tests, the confidence limits are based on a small sample size resulting in a larger spread in the confidence limits. A larger sample size would narrow the confidence limits and pull the lower limits within the compliance assuming that all other conditions (average and standard deviation) remain the same. One of the "DRY" soil tests (B6 redo) also achieved the 95% Standard Proctor Density at a 95% confidence level. The other dry test fell well short of the acceptance criteria. All of the "Wet" conditions include all the 1998 tests and those results were discussed in the 1998 CL Tests section.
SOIL BALL TEST FOR CLAY
In this case, the soil ball test was misleading. A much lower moisture condition is required than is indicated by the soil ball test. For fine and highly plastic materials, the "GOOD" soil ball may have to be redefined. However, it should be noted that these soils are not best for good compaction and should be avoided if possible.
During the 1999 Clay Tests, care was taken to dry the soil to just dry of optimum moisture (as defined by the Standard Proctor Test) and the very dry optimum moisture. Soil ball tests were then conducted as defined in the "Backfilling and Compaction Guidelines". The very dry soil did not form a soil ball and in agreement with the Guidelines is determined to be "Dry" and not suitable for good compaction. The soil that was just dry of optimum and was of a moisture content suitable for good compaction, formed a firm ball, which broke into two or three lumps. The lumps were firm and well bonded. This is also in agreement with the "Guidelines". The wet soils tested in 1998 produced soil balls that were firm but did not drip water. The "Guidelines" mislabel this result as "Good" moisture content. For clays, the soil ball test should be "Good" soils form a ball that breaks into large firm chunks. If it does not break into chunks, it is "Wet" and not suitable for compaction.