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CHAPTER 4
Conclusions
Several modifications to the SPT equipment specification, identified that the length of the gauge point in the direction
the SPT test methods, and the equipment supplied by the of the strain measurement had a significant effect on the
three manufacturers were made as a result of the ruggedness measured dynamic modulus. In the final version of the SPT
and equipment effects experiments. These modifications are equipment specification, a maximum dimension for the
discussed below. gauge point in this direction was added. Finally, the new flow
number algorithm developed at ASU using the Franken
model produced reduced variability in flow number test re-
4.1 SPT Equipment Specification
sults with the SPT. The final version of the SPT equipment
Modifications
specification was modified to include flow number computa-
The ruggedness and equipment effects experiments con- tions based on the Franken model. The final version of the
firmed that the SPT equipment specifications developed in SPT equipment specification is included as Appendix E.
NCHRP Project 9-29 are appropriate. The ruggedness test-
ing demonstrated that the level of control required by the
4.2 SPT Test Methods
SPT equipment specifications provides precise data for the
Modifications
dynamic modulus and flow number tests. Because the flow
number and flow time tests are very similar, this conclusion Two changes to the SPT test methods were also made as a
can also be extended to the flow time test. The equipment result of the ruggedness and equipment effects experiments.
effects experiment demonstrated that there is little differ- First, the ruggedness testing clearly showed that the flow
ence in dynamic modulus and flow number data collected number test results were significantly affected by the type of
with equipment meeting the SPT equipment specification end friction reducer used. The SPT test methods were revised
supplied by three manufacturers. Significant differences in to specify the use of greased latex membranes friction reduc-
dynamic modulus were detected only for tests resulting ers in the flow number test. A standard method for preparing
in modulus values below about 500 MPa. Differences in the greased latex membranes was also added. The second
flow number test data between machines from different change to the SPT test methods was the addition of a check
manufacturers were confined to the early portion of the on the direction of the drift in the dynamic modulus test as a
permanent deformation curve and were not of engineering data quality indicator. During the equipment effects experi-
significance. ment, it was discovered that the spring force of the LVDTs
Three SPT equipment specification changes were identified could result in drift that tended to move the gauge points fur-
by the by the ruggedness and equipment effects experiments. ther apart. The drift compensation included in the dynamic
First more precise control of strain is needed in confined modulus computations is not intended to remove this form
dynamic modulus tests compared to unconfined tests. Based of drift; therefore, a significant error in the dynamic modulus
on the ruggedness testing, strain in confined dynamic modulus can result if the gauge points move apart during the test. The
tests should be controlled to within ±15 strain of the data quality check that was added is to accept only data where
100 strain target. The SPT equipment specifications included the drift is in the same direction as the applied load. A stan-
a strain control tolerance of ±25 strain. The tolerance was dard test method for conducting dynamic modulus and flow
reduced to within ±15 strain in the final version of the number tests in the form of an AASHTO standard is included
SPT specification. Second, the equipment effects experiment in Appendix F.
