Development of a Small Diameter Rapid Pressuremeter Test for Unbound Pavement Layer Evaluations
Misilo, Thaddeus Joseph
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Six inch and 12 inch long small diameter pressuremeter (SDPMT) probes were developed and tested extensively to determine in situ stress-strain properties of unbound pavement layers. They were deployed in the same hole as the one made during nuclear density testing. The stress strain response of conventional or incremental and continuous or rapid strain controlled tests in unbound pavement layers were evaluated at four sites in Brevard County, Florida. One test site was A-1-b base material, one was A-3 subgrade and two were compacted A-3 fill of subgrade quality. The SDPMT results were compared with nuclear density dry and wet soil unit weights, moduli from the Dynatest and Zorn light weight deflectometers, impact values from Clegg impact tests, and index values from dynamic cone penetrometer (DCP) tests. The SDPMT tests were conducted by driving or drilling a hole 7 or 13 inches deep, then inserting a 5/8 inch diameter 6 or 12 inch long expandable cylindrical probe. Once the probe was in place, it was inflated with water as the soil stress-strain response was monitored and digitally recorded. Five statical models were used to evaluate the relationships between the pressuremeter parameters and the results from the other testing. The models produced linear, logarithmic and exponential correlations. The testing phase of this research included 159 SDPMT tests. Additionally 107 nuclear density tests, 141 lightweight deflectometer tests, 96 Clegg impact hammer tests, 36 dynamic cone penetrometer tests were preformed to evaluate their relationship with the pressuremeter parameters. SDPMT engineering parameters were consistent and comparable to published results. The rapid SDPMT testing was completed in less than 3-minutes and provided reliable data, indicating that with further refinements, these test could compliment and possible replace nuclear density testing. It was observed that the resulting stress – strain response from the incremental and continuous 6 and 12 inch tests resembles those of the standard PENCEL pressuremeter curve. This study also demonstrates that SDPMT data match common pressuremeter parameters for sands. This study showed p0 is the least useful engineering parameter of those generated during testing. The E0/pL ratio for incremental SDPMT tests ranged from 7.0 to 16.1 for both 6 and 12 inch probes, which is similar to Briaud’s (2005) published relationship of 7 to 12 range. Therefore the test quality is acceptable. E0/pL for rapid or continuous SDPMT tests ranged from 10.9 to 33.2 for the 6 and 12 inch probes. Although this is higher than the upper range of 12, the higher values are attributed to the increased strain-rate applied to the soil during rapid testing. Data collected during this research shows an excellent correlation between densities and both E0 and pL for all test configurations. The excellent E0 verses pL R2 from the 12 inch incremental testing suggested that engineers may be able to predict pL from E0. Logarithmic relationships were observed between densities and E0 and pL. Good to excellent stiffness correlations exist between SDPMT moduli and LWD moduli as nearly all R2-values exceeded 0.70. SDPMT E0 - LWD moduli correlations were higher for the Dynatest LWD than the Zorn LWD. An excellent logarithmic correlation between the Clegg impact value and the SDPMT initial moduli for both 6 inch and 12 inch incremental tests. No correlation was found between the DCP Index and the SDPMT p0, pL or E0.