Correlation Between MWD Compound Parameters and SPT N-values in Nebraska-Paper

Paper

Pdf Summary

The study evaluates whether Measurement While Drilling (MWD) data can predict Standard Penetration Test (SPT-N) values in fine-grained soils. Data were collected from four Nebraska boreholes drilled with a mud-rotary method and tricone bits. Five compound MWD parameters—specific energy, drillability, Somerton index, soil-rock resistance, and alteration index—were averaged over different 12- and 18-inch intervals and compared with SPT-N values.<br /><br />SPT refusal tests, assigned an N-value of 100, introduced substantial scatter and reduced correlation accuracy. The authors recommend excluding refusals unless a more suitable way to represent them is developed. Correlations were generally strongest when MWD measurements were averaged over the same depth interval as the SPT test, despite disturbance from the test. Both interval lengths performed similarly in terms of fit, but the selected length must be used consistently.<br /><br />Somerton index and soil-rock resistance showed the strongest relationships with SPT-N, with coefficients of determination of 0.97 and 0.91, respectively, for the 12-inch same-depth interval. Alteration index and specific energy had more moderate correlations, while drillability performed less well.<br /><br />The findings are preliminary: they are based on a small dataset of silts and clays, and the SPT-N values were not corrected for overburden pressure. Further research, including separate analyses by soil plasticity, is needed before the correlations can be generalized.

Keywords

Measurement While Drilling

MWD

Standard Penetration Test

SPT-N

fine-grained soils

boreholes

Somerton index

soil-rock resistance

specific energy

drillability