Alternative Title

NCKRI Symposium 2: Proceedings of the Thirteenth Multidisciplinary Conference on Sinkholes and the Engineering and Environmental Impacts of Karst



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University of South Florida

Publication Date

May 2013


Sinkholes and sinkhole-related features in west-central Florida are commonly identified from surface penetration test (SPT) borings, which are located, in part, based on the results from ground penetrating radar (GPR) surveys. SPTs and GPR profiles yield complementary information-SPTs can indicate the presence of low-density soils or voids, while GPR profiles can resolve shallow stratigraphic indicators of subsidence. In GPR profiles collected at 103 residential sites in covered-karst terrain in west-central Florida, sinkhole-related anomalies were identified where GPR reflectors show downwarping, discontinuities, or sudden increases in amplitudes. We analyze the degree to which the shallow features imaged in GPR correlate spatially with the N-values (blow counts) derived from SPTs at 103 residential sites. Results are used to examine (1) which SPT indicators show the strongest correlations with GPR anomalies, (2) the degree to which GPR surveys improve the placement of SPT borings, and (3) what these results indicate about the structure of sinkholes at these sites. We find a statistically significant correlation between GPR anomalies and low SPT N-values with a confidence level of 90%. Logistic regression analysis shows that the strongest correlations are between GPR anomalies and SPT values measured in the depth range of 0-4.6 m. The probability of observing a GPR anomaly on a site will decrease by up to 84% as the minimum SPT value increases from 0 to 20. Boreholes drilled on GPR anomalies are statistically significantly more likely to show zones of anomalously low SPT values than boreholes drilled off GPR anomalies. The odds ratio depends on how the threshold criteria for low N-values are defined, with a maximum observed odds ratio of 2.89. Several statistical results suggest that raveling zones that connect voids to the surface may be inclined, so that shallow GPR anomalies are laterally offset from deeper zones of low N-values. -- Authors Open Access - Permission by Publisher See Extended description for more information.


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