Correlating Strength and Stiffness Data of the PENCEL Pressuremeter and Triaxial Compression Tests in Florida Sands
Jansen, Jacob William
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The poorly graded sands found throughout Florida provide geotechnical engineers with a difficult challenge when performing testing samples in laboratory tests. These challenges have caused lab tests such as the triaxial compression test to be overlooked. Since geotechnical engineers estimate strength and stiffness parameters from basic field tests, they often produce overly conservative designs. Understanding how the automated in-situ PENCEL Pressuremeter (PPMT) test correlates with the triaxial compression test can reduce the time and costs associated with laboratory triaxial testing. Results from triaxial tests yield a Young’s Elastic Modulus, shear strength, and internal friction angle. Results from a PPMT test yield a pressuremeter modulus, lift off pressure, and a limit pressure. The different types of outputted data do not allow for direct comparisons to be made between the triaxial compression test and the PPMT test. This research seeks to correlate the outputted data. This research involved twenty PPMT tests performed in poorly graded sands, with loose to medium dense texture. PPMT results were compared with results from twenty-one triaxial compression tests performed using soil removed from the test sites. The triaxial test density ranged from 20% to 65% of the soils relative density. An equation from Baguelin (1978) was proven to correlate triaxial shear strength with PPMT limit pressure. Correlations indicate that triaxial elastic modulus and triaxial shear strength correlate moderately well. The triaxial modulus is 93 times greater than the shear strength. The PPMT modulus correlates well with the limit pressure, the PPMT modulus is 8.3 times greater than the limit pressure in loose to medium dense sands (R² =0.89). The triaxial elastic modulus and PPMT elastic modulus correlation show PPMT moduli being on average 60% greater than triaxial moduli in similar density and confining conditions. The correlations from this study indicate that data from the triaxial compression test and the PPMT test can be correlated.