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37 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.